The Recent F/stop Controversy

Started 3 months ago | Discussions
Guy Parsons
Guy Parsons Forum Pro • Posts: 32,451
Re: The Recent F/stop Nonsense
1

threw the lens wrote:

The f-stop is only slightly weird in that a smaller number lets in more light. Apart from that, I'm fine with it.

That's because it should always be written as f/stop and never f-stop.

The number is a part reciprocal expression so of course the bigger the f/stop number, the smaller the result.

It's just the same as shutter speeds 1/10 sec lets in more light than 1/1000 sec, again it's a case that may be seen as a "smaller number lets in more light". Again it's a reciprocal.

I simply cannot see why something as basic as f/stop "discussions" makes threads head for 150 count at warp speed. You guys must have absolutely nothing to do with your time....... dammit here I am doing the same....

Regards..... Guy

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kiwi2
kiwi2 Veteran Member • Posts: 4,613
Re: The Recent F/stop Controversy

Great Bustard wrote:

kiwi2 wrote:

Michael Fryd wrote:

Yes. modern cameras are labeled in f/stops, and actual mm. Yet we routinely suggest that people think in terms of effective f/stops, and effective focal lengths.

I am suggesting that instead of "effective f/stop" we use the more straightforward "aperture diameter."

Here is a shot taken with a 6 mm aperture...

6 mm aperture

Here is a shot taken with a 150 mm aperture in the same light with the same camera with the same shutter speed and ISO...

150 mm aperture

Which one put more photons onto the sensor..?

The first, because it gathered light from a way, way, way larger portion of the scene. For example, let's say that the first photo was taken at 24mm f/4 (24mm / 4 = 6mm) and the second taken at 1200mm f/8 (1200mm / 8 = 150mm) both with the same exposure time and ISO setting (for a given scene, relative aperture, and exposure time, the ISO setting affects the lightness of the photo, not the amount of light that made it up).

The 24mm f/4 photo is gathering light from 2500x as much of the scene as the 1200mm f/8 photo. However the 1200mm f/8 photo has an aperture with 625x more area. Thus, 2500 / 625 = 4x (2 stops) more light is being projected on the sensor for 24mm f/4 as 1200mm f/8, assuming the same average scene luminance and exposure time. Clearly, it's easier to simply say f/4 is two stops brighter than f/8, but the above is *why* f/4 is two stops brighter than f/8 (more scenarios explained in detail here).

All that said, I wish to make it clear that I am *not* an advocate of replacing relative apertures (e.g. f/4) with effective apertures (e.g. 6mm). I'm absolutely fine with the system as is

However, when comparing light gathering across formats, it is the effective aperture that is relevant, not the relative aperture. Specifically, for a given scene, exposure time, and effective aperture diameter (*not* relative aperture), the same total amount of light is projected on the sensor (the DOFs will also be the same if the photos are taken from the same position). For example, with regards to *both* light gathering and DOF (diffraction as well), f/4 on mFT is equivalent to f/8 on FF because the aperture diameters are the same for a given [diagonal] angle of view.

The first one was 12mm f/2 and yes the last one 1200mm f/8.

So 4 stops difference. Or 16 times more light with the 12mm f/2.

See how easy that was.

It also shows how you cannot just look at aperture size alone in isolation of the focal length. Doing so tells you nothing about how much light you're putting onto the sensor.

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Great Bustard Forum Pro • Posts: 43,009
Re: The Recent F/stop Controversy
1

kiwi2 wrote:

Great Bustard wrote:

kiwi2 wrote:

Michael Fryd wrote:

Yes. modern cameras are labeled in f/stops, and actual mm. Yet we routinely suggest that people think in terms of effective f/stops, and effective focal lengths.

I am suggesting that instead of "effective f/stop" we use the more straightforward "aperture diameter."

Here is a shot taken with a 6 mm aperture...

6 mm aperture

Here is a shot taken with a 150 mm aperture in the same light with the same camera with the same shutter speed and ISO...

150 mm aperture

Which one put more photons onto the sensor..?

The first, because it gathered light from a way, way, way larger portion of the scene. For example, let's say that the first photo was taken at 24mm f/4 (24mm / 4 = 6mm) and the second taken at 1200mm f/8 (1200mm / 8 = 150mm) both with the same exposure time and ISO setting (for a given scene, relative aperture, and exposure time, the ISO setting affects the lightness of the photo, not the amount of light that made it up).

The 24mm f/4 photo is gathering light from 2500x as much of the scene as the 1200mm f/8 photo. However the 1200mm f/8 photo has an aperture with 625x more area. Thus, 2500 / 625 = 4x (2 stops) more light is being projected on the sensor for 24mm f/4 as 1200mm f/8, assuming the same average scene luminance and exposure time. Clearly, it's easier to simply say f/4 is two stops brighter than f/8, but the above is *why* f/4 is two stops brighter than f/8 (more scenarios explained in detail here).

All that said, I wish to make it clear that I am *not* an advocate of replacing relative apertures (e.g. f/4) with effective apertures (e.g. 6mm). I'm absolutely fine with the system as is.

However, when comparing light gathering across formats, it is the effective aperture that is relevant, not the relative aperture. Specifically, for a given scene, exposure time, and effective aperture diameter (*not* relative aperture), the same total amount of light is projected on the sensor (the DOFs will also be the same if the photos are taken from the same position). For example, with regards to *both* light gathering and DOF (diffraction as well), f/4 on mFT is equivalent to f/8 on FF because the aperture diameters are the same for a given [diagonal] angle of view.

The first one was 12mm f/2 and yes the last one 1200mm f/8.

So 4 stops difference. Or 16 times more light with the 12mm f/2.

Assuming the same average scene luminance, yep.

See how easy that was.

Indeed.

It also shows how you cannot just look at aperture size alone in isolation of the focal length.

Absolutely.

Doing so tells you nothing about how much light you're putting onto the sensor.

It tells you a little.  For example, if the aperture diameter is doubled, 4x as much light will be projected on the sensor, all else equal, but it doesn't tell you how much light that is.  However, I want to once again reiterate what I highlighted in bold above.

kiwi2
kiwi2 Veteran Member • Posts: 4,613
Re: The Recent F/stop Controversy

Great Bustard wrote:

kiwi2 wrote:

It also shows how you cannot just look at aperture size alone in isolation of the focal length.

Absolutely.

So maybe you should tell Michael Fryd that...

www.dpreview.com/forums/post/62879713

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Michael Fryd
Michael Fryd Forum Pro • Posts: 11,559
Re: The Recent F/stop Controversy

Bill Ferris wrote:

Michael Fryd wrote:

Bill Ferris wrote:

Michael Fryd wrote:

...

Thank you for responding and adding to your comments.

If we know the total light gathered but don't know if a smartphone sensor, a medium format sensor or something in-between in size was the mode for using pixels to capture that light, how are we in a better-informed state than knowing an image was made at f/4, but not knowing the scene brightness or shutter speed? The same total volume of light may correspond to a blown out, uniformly white image at base ISO for a smartphone while appearing reasonably exposed at base ISO on medium format. Even on the same format sensor, a too high ISO or a too low ISO can significantly impact and limit the quality of the image we're able to make with a fixed total amount of light.

What you are actually asking about is how a photographer can determine when he has run out of headroom for increasing total light captured.

No, that's not what I asked. You've stated, "total light gathered tells us useful information about the final image without knowing the specifics of either the pixel or sensor size." My question is, knowing only the total light gathered, how do we know of the image is properly exposed, underexposed or overexposed? If you want to answer within the context of ability to recover details in the highlights and shadows, fine. But we both know that, limited only to knowing the total light gathered, we can't know if details will be lost due to over- or underexposure.

You're still thinking in terms of film.   Traditionally "Proper exposure" means that our exposure hit the sweet spot on the film's S-shaped response curve.   Miss that spot, and the negative is too dense or too light to get a good image.

Digital doesn't have the same sort of response curve.  There's a wide range of  exposures that produce a good quality raw file.

However, if we want to pretend that digital acts like film, we need to pretend that there is a "correct exposure".  Therefore we have to pick one.   Generally we say that we have "correct exposure" when the image lightness of the camera produced preview looks good.

Of course, what we really are saying is that the "correct exposure" is one where the exposure is a good match for the selected ISO.

I'm going to suggest that "correct exposure" is the wrong terminology.  The correct terminology is "correct ISO".  With digital there is no need to set the ISO and them make the exposure match.  With digital you pick aperture and shutter, and then pick the ISO that corresponds to that exposure.

So the question of whether a digital image is "properly exposed" doesn't make sense unless we pretend that digital acts like film.

Total light gathered does give us a reasonable idea as to how noisy the image will be.  This is similar to shutter speed which affects motion blur, and aperture which affects depth of field.

The answer is that digital cameras contain very sophisticated computers and can tell us.

All we are talking about is changing the scale from light per unit area, to light collected relative to what the camera can handle.

Cameras have limits on how wide or narrow the aperture can be. How fast/slow the shutter can be. And how much/little light can be recorded.

A hundred years of film photography has trained us that the light limits are more significant than the other two. This is no longer the case with digital.

What you're talking about, is the ambient brightness of the scene. Or, in the absence of ambient illumination, illumination added to the scene by the photographer. I submit that, if there is no light and no available option for adding light, aperture diameter and shutter speed are irrelevant. It is literally impossible to make a photograph without electromagnetic radiation (typically visible light) to which the medium is sensitive. Light, is and will always be the first and most important consideration.

Yes, if there is no light there can be no picture.   Similarly, a camera may not be able to capture a useable image if there is too much light.

There are also situations where the camera does not have enough depth of field to get the entire subject in focus, or doesn't have a fast enough shutter to prevent motion blur.

These are situations which lie outside the shooting envelope of the camera.  For instance a particular shot may lie inside the shooting envelope of a full frame camera with a maximum shutter speed of 1/8000, but outside the shooting envelope of a camera that maxes out at 1/2000.

Within this context, I would say it is more accurate to describe, f-stop, as a concept adopted as a tool of photography than as a concept linked more closely to film or any other mode of containing the light-sensitive medium. The term has no different meaning to a photographer using a chemical emulsion (e.g. glass plate, tin type, film) than to a photographer using pixels (e.g. CCD or CMOS) to capture light. It has no different influence on exposure.

The tradition of describing apertures as the ratio is intended to make it easy to hit a particular target exposure (light per unit area) on the film.

Obviously, it tells us the light per unit area when shooting digital, or other light sensitive mediums.

This and the fact that, regardless of the medium or mode, the same scene brightness, shutter speed and f-stop deliver the same exposure, make f-stop more informative to the photographer. The same f-stop can be achieved using a plethora of combinations of focal lengths and aperture diameters. The same aperture diameter can, within the context of the same scene brightness and shutter speed, deliver a wide range of exposures...a small number of which will be to our liking while the vast majority will be failures.

Again, you are assuming that there is an advantage to the photographer to being able to get the same exposure on two different cameras.

Suppose I have a full frame camera, and I am getting a perfect image shooting a 50mm lens at f/4, 1/60 and ISO 400.

The camera breaks, and I put out my 2X crop body to continue shooting.  Why would I want to match the full frame exposure (light per unit area) on the 2X crop body?

If I was shooting film, matching the exposure is critical.  If I don't I won't have a useable negative.

If I am shooting digital, matching the exposure will give me different results.  At the same exposure, the 2X crop body will give me a noisier result.  At the same f/stop, the 2X crop body will also give me deeper depth of field, and more diffraction blur.

If I am not shooting film, why would I want to keep the same exposure on my backup camera?  Why not use the exposure that gives me the same results?  (which will be an exposure that has the same total light, and same aperture diameter).

My point is that with digital this implementation detail is not that important in terms of what we will see in the final image. Therefore we are better off with a system that backs out unneeded implementation details.

When freed from the need to be a slave to traditional S-shaped film response curve, we have the opportunity to elevate the priority of depth of field and the field of view.

What is the direct relationship between the total amount of light captured and either depth of field or field of view? How about the degree to which motion within the scene is frozen.

Assuming the same subject, any combination of focal length, sensor size, shutter speed and f/stop that yield the same angle of view, depth of field and motion stopping captures the same total light. This is independent of sensor size.

Depth of field and angle of view are understood within the context of focal length, aperture diameter and distance to subject. Scene brightness and total light captured are irrelevant.

Actually the camera factors are angle of view and aperture diameter.  You don't need to know the focal length and f/stop in order to compute depth of field.

However, if you have focal length and f/stop you can use the more complicated formula that compute angle of view and aperture diameter, and then the depth of field.

Total light enters into it because if you have the same angle of view, same shutter speed, and same aperture diameter, you will also have the same total light (assuming the same subject).

This relationship strongly suggests that the underlying important factors are aperture diameter, angle of view, subject illumination, and shutter speed.

Knowing f-stop and focal length, one can easily determine aperture diameter. One can manage both angle of view and depth of field by making changes to f-stop, focal length and distance to subject. It's not necessary to know the aperture diameter. There is no control or display on the camera or lens thay will tell you the aperture diameter being used. Knowing the aperture diameter is not necessary to the task of controlling depth of field. It's not even all that relevant top angle of view.

Actually most lens descriptions list the formula for the aperture diameter.  When you say that the focal length is 100mm, and the aperture diameter is 1/4 the focal length (normally written as "f/4") you are just using a complicated way of saying a 25mm aperture diameter.

With respect to f-stop, a particular setting provides some indication that a shallow or deep depth of field for that focal length was used or that a relatively wide or narrow aperture diameter for that focal length was used.

Yes. The combination of f/stop and focal length provide an indication of depth of field. That's because they provide the two factors you need to know in order to determine aperture diameter.

It's easier to just work directly from aperture diameter.

Distance to subject is also a relevant factor. To be clear, I'm not arguing that aperture diameter is not a factor determining depth of field. However, putting that characteristic front & center is made very difficult for most photographers by the absence of any camera or lens setting or display that tells a photographer what the aperture diameter is. How do propose making that number readily available? More important, what are photographers not able to accomplish as a result of not having that measurement readily available?

Yes, distance is a relevant factor, however, for the sake of simplicity, I am only listing the factors we are discussing.

In terms of the camera not telling the photographer the aperture diameter, that's generally not true.   My lens is labeled 50mm, and my camera might tell me the aperture diameter is set 1/8 of that value.

I submit, there is no creative goal that cannot be achieved by virtue of not knowing the aperture diameter. Isn't that, ultimately, the deciding factor in any argument for change? For real change to be embraced and effected by those who are impacted by the change, there must be done tangible, positive benefit to themselves, the community or organization they're part of. Replacing f-stop with aperture diameter or exposure with total light captured yields no tangible, practical benefits.

You need to know (or have enough information to compute) the aperture diameter in order to make creative decisions about depth of field and overall image noise.

You don't need to know focal length, f/stop or sensor size.  Nor do you need enough information to compute those values.

My point, is that either number in isolation isn't fully instructive. However, as f-stop is one of only two camera settings determining exposure and as it is directly under the control of the photographer, f-stop is - along with shutter speed - a control a photographer benefits from mastering. Mastering an understanding of f-stop has positive impacts both technically and creatively.

Yes. modern cameras are labeled in f/stops, and actual mm. Yet we routinely suggest that people think in terms of effective f/stops, and effective focal lengths.

I only suggest folks think in effective or equivalent terms when comparing different formats. For the purposes of doing or talking about photography with a specific camera and lens, there is no need to bring up equivalence as a consideration.

Yes.  If you only use one system, and you won't ever use another system, there is no need to know how to compare your system to others.

However, that doesn't mean there is an advantage to adding implementation details to the explanation.

I am suggesting that instead of "effective f/stop" we use the more straightforward "aperture diameter."

What are the practical impacts and tangible, real world benefits of your proposal? How does a photographer get that number? Where on the camera or lens do they look to see the aperture diameter displayed? What creative outcome that we currently are unable to accomplish, becomes doable by making this number readily available? Which creative outcome that is presently difficult to accomplish, becomes much easier to achieve? What are the negative consequences of displaying an aperture diameter as opposed to an f-stop?

Well, we started with the question should we get rid of the f/stop.  I think there is a good case to be made the we should deemphasize that terminology and emphasize aperture diameter instead.

Digital cameras have a lots of computational power and sophisticated displays.  I think camera firmware should be helpful enough to display the aperture diameter.

The creative advantage is that it reduces the amount of mental calculations one needs to do.

Assume you move closer to your subject and change the focal length to maintain the same framing.   If the aperture diameter remains the same, you get the same depth of field.   If the f/stop remains the same, the depth of field changes.

While knowing the total amount of light can, within the context of the collection area of the medium, inform an understanding of whether or not we've captured enough light to make (in one's opinion) a quality image, that number doesn't translate to any specific depth of field. It doesn't inform our understanding of the degree to which action has been frozen. It doesn't indicate any particular angle of view.

Total amount of light informs us on the subject of shot noise.

We are able top make decisions about acceptable shot noise, now, using scene brightness, shutter speed and f-stop to control exposure, and ISO as an indicator of acceptable exposure.Aperture diameter and angle of view inform us on the subject of depth of field and subject framing.

Not really. That's not enough information.  You don't have enough information to determine total light captured, so you can't predict how noisy the image will be.

ISO 400, f/4, 1/60 might result in a noisy image if you are using a smart phone, and a clean image of you are using full frame.

Exposure alone (light per unit area) is not enough to determine shot noise.  You need to know the sensor area so you can consider total light captured.

Photographers already control depth of field using focal length, f-stop and distance to subject.

Not really.  you need to add sensor size in there or you can't determine depth of field.  You need to know the sensor size you you can convert f/stop to aperture diameter and the figure out the angle of view.

Individually none of these tell us the whole story. Yet if we know these we can predict the results without knowing sensor size or focal length.

We're already able to predict the results without giving aperture diameter or total light captured any consideration.

Only because you are using formula that take total light and aperture diameter into consideration.  If you don't have enough information to determine diameter and total light, then you don't have enough information.

Now if you know diameter and total light, you don't need enough information to computer focal length.

If anything, I might suggest we go another direction. Rather than focus on the total amount of light captured, let's consider the light available from the subject. Without using a device to measure and quantify the available light, we can still have an informed sense of what the possibilities are. Outside on a bright, sunny day (an abundance of light from the subject), we can have confidence in being able to use a fast shutter speed to capture enough light from a soccer player to make quality images. Outside on a clear, dark, moonless night (minimal available light from the subject), we can have confidence in needing a fast f-stop and a slow shutter speed to capture enough light for a quality image in a single exposure.

If you want to look at the source, we need to look at subject illumination, frame size, and the needed depth of field.

However none of this tell us whether we need a "fast" f/stop. A "fast" f/2.8 lens may be overkill to capture the shot on a full frame, and not nearly enough on a smart phone.

The problem is that on the full frame the f/2.8 lens probably has a larger aperture diameter than the smart phone's f/2.8 lens.

On the contrary and as stated, seeing and making a rough evaluation of scene brightness goes a long way toward informing the choices of f-stop and shutter speed made by a photographer. An experienced photographer will notice a change to the quality of light and adjust f-stop or shutter speed - almost instinctively - to preserve a desired exposure. This happens every day, thousands of times a day all over the world.

Again, this is where we differ.

Why is preserving proper exposure so much more important than preserving proper depth of field and proper shutter speed?

Knowing the f/stop is only useful if we know the sensor size, so we can determine the aperture diameter.

The profound physical and performance differences between chemical emulsions and pixels along with the relative performance characteristics of the modes (glass plates, tin types, film stock, sensor formats) used to precisely positioning these light-sensitive media at the image plane introduce a host of issues relevant to the photographic process. Equivalence, is but one. Frankly, there are too many to adequately address in a collection of books, let alone a single online forum discussion thread.

However, f-stop, is a term having a clear definition. Any lack of clarity on that point in this post, is my failure; not a failure of the long-established and accepted definition of the term. Its meaning and role in determining exposure are the same, regardless of the medium or mode used in the photographic process.

The meaning of f/stop is clear. What changes with digital is the priority of hitting a particular light per unit area.

I'm not sure I agree with this last comment.

Over time using a variety of digital cameras, it's common to develop a personal sense of one range of ISOs indicating an optimal exposure and another ISO range indicating a minimum acceptable exposure. Admittedly, I have no sense at all how many photons I'm capturing from a subject. But using ISO as an indicator of scene brightness, I can have a pretty good idea if the resulting image will be to my liking.

To be clear, I'm using ISO as an indicator of exposure. It's an indicator of the light available in the scene and delivered (as determined by f-stop and shutter speed) to the sensor. Arguably, the greatest strength of giving f-stop a priority over total amount of light in this analysis, is that f-stop has the same meaning, regardless of medium or format, while the same total amount of light can translate to very different outcomes in those areas.

So, while pixels may be able to deliver a quality image at a lower exposure than film, we still have an appreciation of optimum and minimum levels of exposure.

Absolutely, humans are smart and capable. We can learn to use overly complicated systems and get good results. This does not mean that the system being used is the best.

I have a manual transmission car. I could label the 5 forward gears with colors rather than numbers. With a little practice I could get a feel for each gear and learn to drive the car. That doesn't mean it wouldn't be easier to label with traditional numbers.

Let's give a bit more thought to your manual vs automatic transmission analogy. I learned to drive manual transmission cars. They're fun, no doubt about it. But for the vast majority of drivers, an automatic transmission vehicle is much easier to drive. That's a tangible, real benefit that changed an industry. People were able to drive anywhere they wanted before the automatic transmission was adopted as the standard. Some folks might even argue that four on the floor was more fun and, in some situations, more charitable. But the fact that the automatic transmission made the task of driving much easier overwhelmed any reservations or resistance.

So, what is the great benefit to photography and photographers that will come from ending the f-stop and exposure talk, and replacing them with aperture diameter and total light captured?

Benefits include:

  • The explanation of how things work is simpler.  It leaves out implementation details that are not important to the result.
  • It moves mental models away from exposure being paramount, and onto a more equal footing for shutter speed and aperture.
  • it is independent of sensor size, which makes it easier to teach or discuss amongst people who may be using different sensor sizes.
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lanefAU
lanefAU Veteran Member • Posts: 6,348
Re: The Recent F/stop Controversy

Yep, just do selfies all the time as most mobile phone photographers.

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mamallama
mamallama Forum Pro • Posts: 56,059
Re: The Recent F/stop Controversy

Michael Fryd wrote:

Bill Ferris wrote:

Michael Fryd wrote:

Bill Ferris wrote:

Michael Fryd wrote:

...

Thank you for responding and adding to your comments.

If we know the total light gathered but don't know if a smartphone sensor, a medium format sensor or something in-between in size was the mode for using pixels to capture that light, how are we in a better-informed state than knowing an image was made at f/4, but not knowing the scene brightness or shutter speed? The same total volume of light may correspond to a blown out, uniformly white image at base ISO for a smartphone while appearing reasonably exposed at base ISO on medium format. Even on the same format sensor, a too high ISO or a too low ISO can significantly impact and limit the quality of the image we're able to make with a fixed total amount of light.

What you are actually asking about is how a photographer can determine when he has run out of headroom for increasing total light captured.

No, that's not what I asked. You've stated, "total light gathered tells us useful information about the final image without knowing the specifics of either the pixel or sensor size." My question is, knowing only the total light gathered, how do we know of the image is properly exposed, underexposed or overexposed? If you want to answer within the context of ability to recover details in the highlights and shadows, fine. But we both know that, limited only to knowing the total light gathered, we can't know if details will be lost due to over- or underexposure.

You're still thinking in terms of film. Traditionally "Proper exposure" means that our exposure hit the sweet spot on the film's S-shaped response curve. Miss that spot, and the negative is too dense or too light to get a good image.

Digital doesn't have the same sort of response curve. There's a wide range of exposures that produce a good quality raw file.

However, if we want to pretend that digital acts like film, we need to pretend that there is a "correct exposure". Therefore we have to pick one. Generally we say that we have "correct exposure" when the image lightness of the camera produced preview looks good.

Of course, what we really are saying is that the "correct exposure" is one where the exposure is a good match for the selected ISO.

I'm going to suggest that "correct exposure" is the wrong terminology. The correct terminology is "correct ISO". With digital there is no need to set the ISO and them make the exposure match. With digital you pick aperture and shutter, and then pick the ISO that corresponds to that exposure.

So the question of whether a digital image is "properly exposed" doesn't make sense unless we pretend that digital acts like film.

Total light gathered does give us a reasonable idea as to how noisy the image will be. This is similar to shutter speed which affects motion blur, and aperture which affects depth of field.

The answer is that digital cameras contain very sophisticated computers and can tell us.

All we are talking about is changing the scale from light per unit area, to light collected relative to what the camera can handle.

Cameras have limits on how wide or narrow the aperture can be. How fast/slow the shutter can be. And how much/little light can be recorded.

A hundred years of film photography has trained us that the light limits are more significant than the other two. This is no longer the case with digital.

What you're talking about, is the ambient brightness of the scene. Or, in the absence of ambient illumination, illumination added to the scene by the photographer. I submit that, if there is no light and no available option for adding light, aperture diameter and shutter speed are irrelevant. It is literally impossible to make a photograph without electromagnetic radiation (typically visible light) to which the medium is sensitive. Light, is and will always be the first and most important consideration.

Yes, if there is no light there can be no picture. Similarly, a camera may not be able to capture a useable image if there is too much light.

There are also situations where the camera does not have enough depth of field to get the entire subject in focus, or doesn't have a fast enough shutter to prevent motion blur.

These are situations which lie outside the shooting envelope of the camera. For instance a particular shot may lie inside the shooting envelope of a full frame camera with a maximum shutter speed of 1/8000, but outside the shooting envelope of a camera that maxes out at 1/2000.

Within this context, I would say it is more accurate to describe, f-stop, as a concept adopted as a tool of photography than as a concept linked more closely to film or any other mode of containing the light-sensitive medium. The term has no different meaning to a photographer using a chemical emulsion (e.g. glass plate, tin type, film) than to a photographer using pixels (e.g. CCD or CMOS) to capture light. It has no different influence on exposure.

The tradition of describing apertures as the ratio is intended to make it easy to hit a particular target exposure (light per unit area) on the film.

Obviously, it tells us the light per unit area when shooting digital, or other light sensitive mediums.

This and the fact that, regardless of the medium or mode, the same scene brightness, shutter speed and f-stop deliver the same exposure, make f-stop more informative to the photographer. The same f-stop can be achieved using a plethora of combinations of focal lengths and aperture diameters. The same aperture diameter can, within the context of the same scene brightness and shutter speed, deliver a wide range of exposures...a small number of which will be to our liking while the vast majority will be failures.

Again, you are assuming that there is an advantage to the photographer to being able to get the same exposure on two different cameras.

Suppose I have a full frame camera, and I am getting a perfect image shooting a 50mm lens at f/4, 1/60 and ISO 400.

The camera breaks, and I put out my 2X crop body to continue shooting. Why would I want to match the full frame exposure (light per unit area) on the 2X crop body?

If I was shooting film, matching the exposure is critical. If I don't I won't have a useable negative.

If I am shooting digital, matching the exposure will give me different results. At the same exposure, the 2X crop body will give me a noisier result. At the same f/stop, the 2X crop body will also give me deeper depth of field, and more diffraction blur.

If I am not shooting film, why would I want to keep the same exposure on my backup camera? Why not use the exposure that gives me the same results? (which will be an exposure that has the same total light, and same aperture diameter).

My point is that with digital this implementation detail is not that important in terms of what we will see in the final image. Therefore we are better off with a system that backs out unneeded implementation details.

When freed from the need to be a slave to traditional S-shaped film response curve, we have the opportunity to elevate the priority of depth of field and the field of view.

What is the direct relationship between the total amount of light captured and either depth of field or field of view? How about the degree to which motion within the scene is frozen.

Assuming the same subject, any combination of focal length, sensor size, shutter speed and f/stop that yield the same angle of view, depth of field and motion stopping captures the same total light. This is independent of sensor size.

Depth of field and angle of view are understood within the context of focal length, aperture diameter and distance to subject. Scene brightness and total light captured are irrelevant.

Actually the camera factors are angle of view and aperture diameter. You don't need to know the focal length and f/stop in order to compute depth of field.

However, if you have focal length and f/stop you can use the more complicated formula that compute angle of view and aperture diameter, and then the depth of field.

Total light enters into it because if you have the same angle of view, same shutter speed, and same aperture diameter, you will also have the same total light (assuming the same subject).

This relationship strongly suggests that the underlying important factors are aperture diameter, angle of view, subject illumination, and shutter speed.

Knowing f-stop and focal length, one can easily determine aperture diameter. One can manage both angle of view and depth of field by making changes to f-stop, focal length and distance to subject. It's not necessary to know the aperture diameter. There is no control or display on the camera or lens thay will tell you the aperture diameter being used. Knowing the aperture diameter is not necessary to the task of controlling depth of field. It's not even all that relevant top angle of view.

Actually most lens descriptions list the formula for the aperture diameter. When you say that the focal length is 100mm, and the aperture diameter is 1/4 the focal length (normally written as "f/4") you are just using a complicated way of saying a 25mm aperture diameter.

With respect to f-stop, a particular setting provides some indication that a shallow or deep depth of field for that focal length was used or that a relatively wide or narrow aperture diameter for that focal length was used.

Yes. The combination of f/stop and focal length provide an indication of depth of field. That's because they provide the two factors you need to know in order to determine aperture diameter.

It's easier to just work directly from aperture diameter.

Distance to subject is also a relevant factor. To be clear, I'm not arguing that aperture diameter is not a factor determining depth of field. However, putting that characteristic front & center is made very difficult for most photographers by the absence of any camera or lens setting or display that tells a photographer what the aperture diameter is. How do propose making that number readily available? More important, what are photographers not able to accomplish as a result of not having that measurement readily available?

Yes, distance is a relevant factor, however, for the sake of simplicity, I am only listing the factors we are discussing.

In terms of the camera not telling the photographer the aperture diameter, that's generally not true. My lens is labeled 50mm, and my camera might tell me the aperture diameter is set 1/8 of that value.

I submit, there is no creative goal that cannot be achieved by virtue of not knowing the aperture diameter. Isn't that, ultimately, the deciding factor in any argument for change? For real change to be embraced and effected by those who are impacted by the change, there must be done tangible, positive benefit to themselves, the community or organization they're part of. Replacing f-stop with aperture diameter or exposure with total light captured yields no tangible, practical benefits.

You need to know (or have enough information to compute) the aperture diameter in order to make creative decisions about depth of field and overall image noise.

You don't need to know focal length, f/stop or sensor size. Nor do you need enough information to compute those values.

My point, is that either number in isolation isn't fully instructive. However, as f-stop is one of only two camera settings determining exposure and as it is directly under the control of the photographer, f-stop is - along with shutter speed - a control a photographer benefits from mastering. Mastering an understanding of f-stop has positive impacts both technically and creatively.

Yes. modern cameras are labeled in f/stops, and actual mm. Yet we routinely suggest that people think in terms of effective f/stops, and effective focal lengths.

I only suggest folks think in effective or equivalent terms when comparing different formats. For the purposes of doing or talking about photography with a specific camera and lens, there is no need to bring up equivalence as a consideration.

Yes. If you only use one system, and you won't ever use another system, there is no need to know how to compare your system to others.

However, that doesn't mean there is an advantage to adding implementation details to the explanation.

I am suggesting that instead of "effective f/stop" we use the more straightforward "aperture diameter."

What are the practical impacts and tangible, real world benefits of your proposal? How does a photographer get that number? Where on the camera or lens do they look to see the aperture diameter displayed? What creative outcome that we currently are unable to accomplish, becomes doable by making this number readily available? Which creative outcome that is presently difficult to accomplish, becomes much easier to achieve? What are the negative consequences of displaying an aperture diameter as opposed to an f-stop?

Well, we started with the question should we get rid of the f/stop. I think there is a good case to be made the we should deemphasize that terminology and emphasize aperture diameter instead.

Digital cameras have a lots of computational power and sophisticated displays. I think camera firmware should be helpful enough to display the aperture diameter.

The creative advantage is that it reduces the amount of mental calculations one needs to do.

Assume you move closer to your subject and change the focal length to maintain the same framing. If the aperture diameter remains the same, you get the same depth of field. If the f/stop remains the same, the depth of field changes.

While knowing the total amount of light can, within the context of the collection area of the medium, inform an understanding of whether or not we've captured enough light to make (in one's opinion) a quality image, that number doesn't translate to any specific depth of field. It doesn't inform our understanding of the degree to which action has been frozen. It doesn't indicate any particular angle of view.

Total amount of light informs us on the subject of shot noise.

We are able top make decisions about acceptable shot noise, now, using scene brightness, shutter speed and f-stop to control exposure, and ISO as an indicator of acceptable exposure.Aperture diameter and angle of view inform us on the subject of depth of field and subject framing.

Not really. That's not enough information. You don't have enough information to determine total light captured, so you can't predict how noisy the image will be.

ISO 400, f/4, 1/60 might result in a noisy image if you are using a smart phone, and a clean image of you are using full frame.

Exposure alone (light per unit area) is not enough to determine shot noise. You need to know the sensor area so you can consider total light captured.

Photographers already control depth of field using focal length, f-stop and distance to subject.

Not really. you need to add sensor size in there or you can't determine depth of field. You need to know the sensor size you you can convert f/stop to aperture diameter and the figure out the angle of view.

Individually none of these tell us the whole story. Yet if we know these we can predict the results without knowing sensor size or focal length.

We're already able to predict the results without giving aperture diameter or total light captured any consideration.

Only because you are using formula that take total light and aperture diameter into consideration. If you don't have enough information to determine diameter and total light, then you don't have enough information.

Now if you know diameter and total light, you don't need enough information to computer focal length.

If anything, I might suggest we go another direction. Rather than focus on the total amount of light captured, let's consider the light available from the subject. Without using a device to measure and quantify the available light, we can still have an informed sense of what the possibilities are. Outside on a bright, sunny day (an abundance of light from the subject), we can have confidence in being able to use a fast shutter speed to capture enough light from a soccer player to make quality images. Outside on a clear, dark, moonless night (minimal available light from the subject), we can have confidence in needing a fast f-stop and a slow shutter speed to capture enough light for a quality image in a single exposure.

If you want to look at the source, we need to look at subject illumination, frame size, and the needed depth of field.

However none of this tell us whether we need a "fast" f/stop. A "fast" f/2.8 lens may be overkill to capture the shot on a full frame, and not nearly enough on a smart phone.

The problem is that on the full frame the f/2.8 lens probably has a larger aperture diameter than the smart phone's f/2.8 lens.

On the contrary and as stated, seeing and making a rough evaluation of scene brightness goes a long way toward informing the choices of f-stop and shutter speed made by a photographer. An experienced photographer will notice a change to the quality of light and adjust f-stop or shutter speed - almost instinctively - to preserve a desired exposure. This happens every day, thousands of times a day all over the world.

Again, this is where we differ.

Why is preserving proper exposure so much more important than preserving proper depth of field and proper shutter speed?

Knowing the f/stop is only useful if we know the sensor size, so we can determine the aperture diameter.

The profound physical and performance differences between chemical emulsions and pixels along with the relative performance characteristics of the modes (glass plates, tin types, film stock, sensor formats) used to precisely positioning these light-sensitive media at the image plane introduce a host of issues relevant to the photographic process. Equivalence, is but one. Frankly, there are too many to adequately address in a collection of books, let alone a single online forum discussion thread.

However, f-stop, is a term having a clear definition. Any lack of clarity on that point in this post, is my failure; not a failure of the long-established and accepted definition of the term. Its meaning and role in determining exposure are the same, regardless of the medium or mode used in the photographic process.

The meaning of f/stop is clear. What changes with digital is the priority of hitting a particular light per unit area.

I'm not sure I agree with this last comment.

Over time using a variety of digital cameras, it's common to develop a personal sense of one range of ISOs indicating an optimal exposure and another ISO range indicating a minimum acceptable exposure. Admittedly, I have no sense at all how many photons I'm capturing from a subject. But using ISO as an indicator of scene brightness, I can have a pretty good idea if the resulting image will be to my liking.

To be clear, I'm using ISO as an indicator of exposure. It's an indicator of the light available in the scene and delivered (as determined by f-stop and shutter speed) to the sensor. Arguably, the greatest strength of giving f-stop a priority over total amount of light in this analysis, is that f-stop has the same meaning, regardless of medium or format, while the same total amount of light can translate to very different outcomes in those areas.

So, while pixels may be able to deliver a quality image at a lower exposure than film, we still have an appreciation of optimum and minimum levels of exposure.

Absolutely, humans are smart and capable. We can learn to use overly complicated systems and get good results. This does not mean that the system being used is the best.

I have a manual transmission car. I could label the 5 forward gears with colors rather than numbers. With a little practice I could get a feel for each gear and learn to drive the car. That doesn't mean it wouldn't be easier to label with traditional numbers.

Let's give a bit more thought to your manual vs automatic transmission analogy. I learned to drive manual transmission cars. They're fun, no doubt about it. But for the vast majority of drivers, an automatic transmission vehicle is much easier to drive. That's a tangible, real benefit that changed an industry. People were able to drive anywhere they wanted before the automatic transmission was adopted as the standard. Some folks might even argue that four on the floor was more fun and, in some situations, more charitable. But the fact that the automatic transmission made the task of driving much easier overwhelmed any reservations or resistance.

So, what is the great benefit to photography and photographers that will come from ending the f-stop and exposure talk, and replacing them with aperture diameter and total light captured?

Benefits include:

  • The explanation of how things work is simpler. It leaves out implementation details that are not important to the result.
  • It moves mental models away from exposure being paramount, and onto a more equal footing for shutter speed and aperture.
  • it is independent of sensor size, which makes it easier to teach or discuss amongst people who may be using different sensor sizes.

Wow!! I just signed a $15,000 contract with a professional wedding photographer for my daughter and I hope he has all this stuff down pat. Otherwise I will be disappointed in the results. 

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fferreres Senior Member • Posts: 2,203
Re: The Recent F/stop Controversy

Great Bustard wrote:

Indeed. However, an important lesson that Equivalence explains is that, for a given DOF and exposure time, the same total amount of light is projected on the sensor for *all* systems.

Correct (except the part "important lesson")

So, for a larger format to have a light gathering advantage over a smaller format, the larger format *must* use a more narrow DOF or a longer exposure time. That's worth knowing, methinks, even if one is otherwise uninterested in other Equivalence related topics.

And the "important lesson" ends in embarrassment, methinks, because it could actually very well be the case that the larger format may not need to do ANYTHING to have a light gathering advantage, because it may spread that light over a larger sensor, and the smaller format may need to increase the DOF or reduce exposure time to actually not clip all the highlights.

So no. It may need to do it. Or it may not need to do it....

Equivalently, ...it really just depends.

** Epilogue **

Equivalence is to Numbers, as Analogy is to Concepts. It works only across a subset of the argument, and thus cannot be stated as Equal. Because it's not Equal, it's just an "Accountants" approach photography, dealing with equivalences that only work " in some ways and fail in some others.

Even things that you can consider result in the same thing, produce results that are NOT equivalent, regardless of your light accounting best practices. A 50mm f1.4 lens will never be a 25mm f1.4. Actually, no lens half the FL and same aperture is same. It cannot be equivalent, because each will have different optical characteristics. But for the Equivalence scientist they are all and indistinguishable ---> depending on what sensor you put behind.

fferreres Senior Member • Posts: 2,203
Re: Really?

Aaron801 wrote:

f-stop is just the standard definition... has been for years. No reason I can see to change it now. Not sure if any of this talk has anything to do with light transmission (or t-stop) but I get that this can be a bit different than the f-stop value. it's not typically a very large difference though and is really only important when you're shooting film/vide, which is why those lenses are rated in t-stops... so it seems that it's all good, right?

Aaron801, nothing to do with t-stops. It's about a new Non Profit that's about to be created by some smart folks that have become so absorbed with the Principle of Equivalence that they are highly likely to start a new official cult with non profit designation and actual churches where they will have 50mm f2 lenses along 100mm f2 lenses in the All Equal Saturday rite.

In some variants, apertures will be designed as perfect circles with certain mm, regardless of aperture shapes and transmission, and in some others every lens will have to be marked in the body with the possible FOV of such lenses for any sensor size ever created, including leaving enough space for all future sensor sizes as well (risking decommission if they ever run out of space).

If this doesn't make sense...well, it doesn't. But you asked what was this all about and that's the best way I can summarize it.

fferreres Senior Member • Posts: 2,203
Re: Really?

Lee Jay wrote:

Aaron801 wrote:

f-stop is just the standard definition... has been for years. No reason I can see to change it now. Not sure if any of this talk has anything to do with light transmission (or t-stop) but I get that this can be a bit different than the f-stop value. it's not typically a very large difference though and is really only important when you're shooting film/vide, which is why those lenses are rated in t-stops... so it seems that it's all good, right?

Well, the basic idea is this:

Sorry, before I start, are you the same person that created the EVF wars stating the EVF made it impossible to track anything?

In the film era, ISO was hard to change and post-processing was usually pretty limited, so you're always stuck trying to get light-per-unit-of-area multiplied by time (f-stop * shutter speed) to be just right. Plus most people (but not all) shot just one format (35mm for example).

At that time, people had apertures and shutter speeds. And had film. And today, we have sensors who's best performance is at for the vast majority ISO 100 (and some other, some other number, fixed as well).

So nothing at all has changed.

I don't use film, never did, and I don't want to use ISO 6400 when I can use ISO 3200. And I don't want to use ISO 400 when I can use ISO 200, or 100. The fact that I can degrade the picture more graciously than before changes nothing. I still want to be able to double and halve the total light getting in (which just happens to be the same in terms of light intensity).

However, in digital none of those three assumptions are true - we can change ISO easily, we can post process like crazy, and many, even most people shoot more than one format (full-frame + 1" compact + 1/2.3" cell phone, for example).

I can NEVER change the ISO and get the same quality, unless if changing it to ISO 100.

Given that fact, and the fact that image quality is not controlled by light-per-unit-area

Which could be correct, if it were to be correct, but it isn't at all. Even the Equivalence high priest will acknowledge that the moment you change the relative light into more the sensor can hold, you overexpose, and the moment you change the relative light to something lower, you just created unneeded noise. BOTH of which affect image quality.

What is THE ONE thing that doesn't change image quality? The right amount of light intensity.

but rather by total light captured (and DOF is actually controlled by the same thing minus the effect of shutter speed),

You are confusing what changes image quality, and what happens where. The right amount of light intensity controls everything. And in a larger sensor, the right amount of light intensity means more total light because ...mhhh...it's a larger sensor.

it makes more sense for some people to think in terms of aperture diameter rather than in f-stop (ratio of focal length to aperture) terms. This keeps things independent of ISO and format.

It makes no more sense to think in term of aperture diameter that in f-stops.

1) f-stops don't make assumptions of aperture SHAPE

2) f-stops don't fumble cultures that don't use mm as their unit of measure, including the vast number of alien cultures that surely frequent you.

3) f-stops can be easily be calculated (what is the next stop after 3.2mm? And after 12.21mm? Before that?

4) f-stops make sense and help photographers with their job

Your mm or any other unit aperture size don't even pass (1) here. The Church of Equivalence merges with the Church of Circular Diaphragms?

I have no issues with f-stop either (it's just math) but there is a logical reason to think in another way.

It's ok. But the issue is not when you state this. The issue is when you present it as making more sense. It doesn't pass test (1), so while it's a useful teaching device (as is the Equivalence concepts) when you elevate it to making more sense, it suddenly fails.

What would really MAKE sense, but will never be adopted anyway because of the inmense number of lenses and cameras marked that way, and because people like that anyway, is to use the EXPONENTS of the f-stops.

f/1 = (2ˆ0)ˆ(1/2) = 1

f/1 = (2ˆ1)ˆ(1/2) = 1.4

f/1 = (2ˆ2)ˆ(1/2) = 2

f/1 = (2ˆ3)ˆ(1/2) = 2.8

...

And call them eg. 0, 1, 2, 3, 4, 5, 6, etc. This would help novices better remember the order. But it also other disadvantages I am probably missing. If on FF and (let's replace f with e) e=1 it will be e=3 in M43. Or if e=4 lens on M43 it will be e=6. Just add 2, the crop factor. Or add if moving to medium format. People would not need to remember the number series: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 32, etc. However, this also may not be better, although it will make more sense than the imaginary mm diameters that don't even exist in any lens (except wide open).

By the way, astro folks have been doing this more-or-less since the dawn of telescopes. Telescopes are almost always sold in terms of aperture diameter rather than focal length, f-stop and format size.

The Alien Connection. And also, many telescopes don't have diaphragms. And thus it COULD make sense due to the lack of diaphragm which would ensure it's shape always be a circle.

LoneTree1 Senior Member • Posts: 1,287
Re: Really?

fferreres wrote:

 

By the way, astro folks have been doing this more-or-less since the dawn of telescopes. Telescopes are almost always sold in terms of aperture diameter rather than focal length, f-stop and format size.

The Alien Connection. And also, many telescopes don't have diaphragms. And thus it COULD make sense due to the lack of diaphragm which would ensure it's shape always be a circle.

Telescopes don't have diaphragms because the idea is that you collect as much light as possible in order to best see the object and (if the scope is diffraction-limited) the larger the aperture, the higher the resolution, which  is proportional to that aperture.  Camera lenses, few being diffraction-limited wide-open, usually need to be stopped-down to achieve the sharpness image with the highest contrast.  Having said that, many telescopes now sold are much faster (shorter f-ratio) than in the past.  This is because of imaging requirements, the need for wider fields of view and the availability of exotic glasses to control aberrations.

fferreres Senior Member • Posts: 2,203
Re: Really?

Michael Fryd wrote:

Aaron801 wrote:

...

I think that I get what you're saying, that the amount of light that a sensor receives is totally different depending on what size it is and therefore the size of the opening of the lens in front of it. Of course f-stop is not the size of the opening but is a ratio... You need to do some math to figure out what the "equivalent aperture" is between different formats... but I'm OK with that.

Actually, at the same angle of view the "equivalent aperture" is the one with the same diameter. In other words it really is the same aperture; no math needed.

Actually, it's not. Not only because I am picky, but because lenses are not required to have circular apertures at all.

What is the diameter of the square?

What is the diameter of a triangle?

What is the diameter of a pentagon?

What is the diameter of a circle?

For of these questions have no answer. Did you know there are other more exotic apertures, some for example with dots? What about mirror lenses (usually fixed aperture). They don't even have a center.

You only need to do the math if you normalize everything to light per unit area (which is a great idea when shooting film).

Actually, no. I don't use film and would still have trouble normalizing a triangle and its newfound diameter. Or have to thing in terms of the amount of light as something related to each individual sensor size.

LoneTree1 Senior Member • Posts: 1,287
Re: Really?
1

fferreres wrote:

Michael Fryd wrote:

Aaron801 wrote:

...

I think that I get what you're saying, that the amount of light that a sensor receives is totally different depending on what size it is and therefore the size of the opening of the lens in front of it. Of course f-stop is not the size of the opening but is a ratio... You need to do some math to figure out what the "equivalent aperture" is between different formats... but I'm OK with that.

Actually, at the same angle of view the "equivalent aperture" is the one with the same diameter. In other words it really is the same aperture; no math needed.

Actually, it's not. Not only because I am picky, but because lenses are not required to have circular apertures at all.

What is the diameter of the square?

What is the diameter of a triangle?

What is the diameter of a pentagon?

What is the diameter of a circle?

For of these questions have no answer. Did you know there are other more exotic apertures, some for example with dots? What about mirror lenses (usually fixed aperture). They don't even have a center.

You only need to do the math if you normalize everything to light per unit area (which is a great idea when shooting film).

Actually, no. I don't use film and would still have trouble normalizing a triangle and its newfound diameter. Or have to thing in terms of the amount of light as something related to each individual sensor size.

Area is area.  Doesn't matter if its a triangle or a circle, it can be calculated and thus the amount of light coming through is known.  There are some  trade-offs.  Diffraction (if the aperture is small enough) can become a real problem with non-circular apertures.  The "spikes" produced when a common six-sided aperture is stopped down are an example. Funny thing though;  most automatic apertures today are not fixed, they don't stop down to f/4.0.  It could just as easily be f/3.456 or whatever had been called for to properly expose the image.  To the camera, a modern lens has clickless apertures.

fferreres Senior Member • Posts: 2,203
Re: Really?
1

Pixel Pooper wrote:

  • Michael Fryd wrote:

Actually, at the same angle of view the "equivalent aperture" is the one with the same diameter. In other words it really is the same aperture; no math needed.

You only need to do the math if you normalize everything to light per unit area (which is a great idea when shooting film).

Whether you are shooting film or digital makes no difference. The reason we use the f/stop is that it gives us the same exposure regardless of focal length or angle of view. If we used aperture diameter it would be more complicated because we would need to change the diameter every time we changed our focal length.

While shooting I am much more likely to change my field of view than my sensor size and if I do change my sensor size it is to take advantage of the differences between the two formats, not to take the same picture on both.

The fact that the same aperture diameter gives the same total light at the same field of view is good to know, but it's not as useful when taking pictures. Whatever format you use, the way to maximize total light is to maximize exposure and your total light is limited by the need to avoid overexposure.

Equivalence is a way of comparing formats, and it is a great framework to understand how things work, but it is not a replacement for f/stops and exposure.

Great comment. Extremely clear. No nonsense. Accurate. Sensible.

Guy Parsons
Guy Parsons Forum Pro • Posts: 32,451
Re: Really?

Simpler systems?

My 1960 Minolta SR1 SLR has a numbering system in an attempt to make things easier, it did not catch on.

I think it was an early attempt at using EV numbers, the aperture goes from f/2 to f/22 with the numbers 2 at f/2 up to 9 at f/22. The shutter speed dial has 0 at 1 sec. and ends with 9 at 1/500 sec. Here's the apertures.....

What's the point anyway, the f/stop and shutter speeds and ISO stuff is so reliable and easy to understand.

People who don't understand should go read a few books about photography and learn what it means.

Regards..... Guy

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fferreres Senior Member • Posts: 2,203
Re: The Recent F/stop Controversy

mamallama wrote:

J A C S wrote:

bolt2014 wrote:

The post about getting rid of the "F/stop" definition turned into such a technical subject that most photographers become lost in the jargon. I think that too many photographers become so embroiled in the technical aspects that they forget that photography is more about being creative .

I do not think we have started yet with the technical aspects. How about this (Wikipedia):

As Rudolf Kingslake explains, "It is a common error to suppose that the ratio [D/2f] is actually equal to tan θ, and not sin θ ... The tangent would, of course, be correct if the principal planes were really plane. However, the complete theory of the Abbe sine condition shows that if a lens is corrected for coma and spherical aberration, as all good photographic objectives must be, the second principal plane becomes a portion of a sphere of radius f centered about the focal point".[4] In this sense, the traditional thin-lens definition and illustration of f-number is misleading, and defining it in terms of numerical aperture may be more meaningful.

Now you have opened Pandora's Box for those who want to outdo the Equivalent genius.

Don't worry, Kingslake became the head of Optical Design department of Kodak, which we know how well it did, and how much we crave for those lenses today.

fferreres Senior Member • Posts: 2,203
Re: It's weird, isn't it?

Great Bustard wrote:

Michael Fryd wrote:

kiwi2 wrote:

Why exactly should I be worried about achieving equivalence between the two..??

You shouldn't be concerned about equivalence between these two.

It's weird that so many [intentionally] misrepresent Equivalence saying that they should be shooting Equivalent photos on different formats, even though Equivalence *explicitly* says quite the opposite. It's as if someone said to multiply mi/hr by 1.6 to get km/hr, and they said, "Why should I drive the same speed in Europe as I do in the US?"

@kiwi2, you shouldn't. You should also not need to know the diameter of iris either, which may have no diameter at all in the first place. Actually, you wouldn't need to know the word Equivalence at all.

Only when people compare formats and make wrong assumptions, and then maybe state inaccurate things (like "M43 is always lesser" or sorts that translate to that) then Equivalence can help bring a better perspective. Or when you mix lenses on cameras with different sensor sizes and want to know what's going on.

Probably, only 1 out of 10,000 photographers need to know of any equivalence. And 3 out 6 billion need to know about the Church of Equivalence yet in their thoughts, it should have 6 billion followers.

fferreres Senior Member • Posts: 2,203
Re: Disingenuous posting
1

Great Bustard wrote:

kiwi2 wrote:

Great Bustard wrote:

Michael Fryd wrote:

kiwi2 wrote:

Why exactly should I be worried about achieving equivalence between the two..??

You shouldn't be concerned about equivalence between these two.

It's weird that so many [intentionally] misrepresent Equivalence saying that they should be shooting Equivalent photos on different formats, even though Equivalence *explicitly* says quite the opposite. It's as if someone said to multiply mi/hr by 1.6 to get km/hr, and they said, "Why should I drive the same speed in Europe as I do in the US?"

So now with a real world example, it suddenly doesn't matter any more...???

Remember when Richard Butler said to you:

Disingenuous posting

It's already been made clear in one thread that no one is saying that the f-number of a lens actually changes and that the standard exposure model is based, for better or worse, on f-numbers and light per unit area.

So no, no one is saying that the f-number "becomes" something else. Or "is" something else on a different sensor. You repeatedly reverting to that claim is clearly disingenuous.

You've made apparent that you know this already. You're also seemingly aware that equivalence doesn't claim it, and that there is some value to a whole-image understanding of total light.

If you continue to intentionally misrepresent the idea of equivalence, purely because you want to play games of semantics or because you've decided you don't deem it useful, this thread will be deleted.

Do you remember that? You're doing the *exact same BS* again. Where does Equivalence say, or imply, that one should use one system to get photos Equivalent to photos taken with another system? Where does Equivalence say, or imply, that the differences between System A and System B are *necessarily* going to be so significant that one *must* take Equivalence into account with each and every photo?

Once again, your are *intentionally* misrepresenting what Equivalence says/implies. Your straw man argument is *exactly* like me posting a photo of a scene at f/4 1/400 ISO 100 and f/8 1/100 ISO 400 that look all but identical and then making the specious claim that there's no difference between f/4 and f/8, no difference between 1/400 and 1/100, and no difference between ISO 100 and ISO 400. And you do this kind of ++++ all the freakin' time!

He did not missrepresent anything. Actually, nobody is opposed to the idea of equivalence. And Richard Butler's own articles about it is probably the bible to understand it. But you remembering a very old post un bringing it an unrelated thread as a threat is something sad.

The problem comes when things that are Equivalent are tried to made Equal. And when in trying to made Equal, they try to reinvent photography by designating lenses with FOV and f-milimeters. Nobody argues about any logical argument of what could eventually compare to something else, as in one dollar in terms of yuans.

Pixel Pooper Veteran Member • Posts: 3,154
Re: The Recent F/stop Controversy
3

Michael Fryd wrote:

Well, we started with the question should we get rid of the f/stop. I think there is a good case to be made the we should deemphasize that terminology and emphasize aperture diameter instead.

If there is a good case for that, you haven't presented it yet.

Digital cameras have a lots of computational power and sophisticated displays. I think camera firmware should be helpful enough to display the aperture diameter.

If you want to know the aperture diameter for some reason just divide the focal length by the f number. It's not difficult, and it's usually not necessary either.

The creative advantage is that it reduces the amount of mental calculations one needs to do.

It reduces the amount of calculations needed to compare different format sizes, but it increases the amount of calculations needed to shoot with the camera you have in your hands. What do you do more of, compare formats or shoot pictures? Hopefully it is the latter.

Assume you move closer to your subject and change the focal length to maintain the same framing. If the aperture diameter remains the same, you get the same depth of field. If the f/stop remains the same, the depth of field changes.

You've got that backwards. When you change focal length and distance to keep the same framing, you get the same DOF at the same f/stop, not the same aperture diameter. The same f/stop also gives you the same exposure and the same total light.

If your camera displayed aperture diameter instead of f/stop you would need to divide your focal length by your aperture diameter, and then divide your new focal length by the result to calculate the aperture diameter needed at the new focal length.

If your camera also displayed angle of view instead of focal length you would have to resort to trigonometry to calculate the required aperture diameter at the new angle of view. Now instead of reducing the number of mental calculations, you have made the calculations too difficult to do mentally.

Benefits include:

  • The explanation of how things work is simpler. It leaves out implementation details that are not important to the result.

You can still explain how things work using aperture diameter, but you will end up having to explain exposure and focal length ratios either way.

  • It moves mental models away from exposure being paramount, and onto a more equal footing for shutter speed and aperture.

Exposure is paramount. If you want the best results from any format you need to maximise total light which means maximising exposure. If you do that you should not use the same aperture diameter and shutter speed on a different format because you would overexpose a smaller sensor or handicap a larger sensor. Instead you would use the same exposure on both formats, but possibly not the same f/stop.

  • it is independent of sensor size, which makes it easier to teach or discuss amongst people who may be using different sensor sizes.

It is independent of sensor size, but it is tied to angle of view. As soon as you use a different angle of view, the same aperture diameter no longer gives the same results. This leaves you with a fairly narrow set of circumstances where aperture diameter is useful. In the end you will have simplified equivalence calculations at the cost of complicating everything else.

Gandolphi Senior Member • Posts: 2,025
Schrödinger's camera

if you are given a sealed box with a camera inside but have no details of the camera is it at the same time, FF,  aps-c, aps-h or four thirds and does equivalence apply...

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