The Recent F/stop Controversy

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Michael Fryd
Michael Fryd Forum Pro • Posts: 11,607
Re: The Recent F/stop Controversy
1

Bill Ferris wrote:

Michael Fryd wrote:

it's not so much a technical question as a philosophical one. Is the frame of reference designed for the limitations of film the best frame of reference to use for digital?

Perhaps, I am misreading your comment and question. It appears you consider f-stop to be more relevant to film than to digital. Or at the very least, you see f-stop as a concept or setting that may be more relevant to film than to digital. Is that accurate?

I would say that for digital photographers the actual aperture diameter is more important than the ratio of focal length to diameter.

Yes, if you know the focal length you can convert from one to the other. But I would say one is better off using the value that's relevant, rather than a related value.

As you and probably everybody participating in this discussion know, the focal ratio of a lens (aka f-stop, f/ratio) describes the ratio of the focal length of the lens to the diameter of the aperture of the lens. Both dimensions are typically measured in millimeters. For example, a 100mm lens with an aperture diameter of 25mm, is described as, f/4. That's the lens's f/ratio. It's the f-stop chosen by the photographer.

Correct.

The use of f-stop to describe the physical characteristics of a lens applies regardless of the light-sensitive medium used. Whether that medium is a chemical emulsion or a collection of pixels, f-stop has the same meaning. Also regardless of the light-sensitive medium used, f-stop along with scene brightness and shutter speed define exposure: the average brightness of the scene at the image plane. This is another fact of which you and most others in this thread are well-aware.

Correct.

But don't forget other implementation details that perhaps are more important that light per unit area. For instance number of photons hitting each pixel.

We tend not to talk about exposure in terms of photons per pixel because that's an implementation detail, and tells us very little about the final image unless we know how many pixels there are.

My point is that with digital, light per unit area (traditionally called "exposure") is an implementation detail, and tells us very little about the final image unless we know the area of the sensor.

On the other hand total light gathered tells us useful information about the final image without knowing the specifics of either the pixel or sensor size.

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.

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.

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.

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Michael Fryd
Michael Fryd Forum Pro • Posts: 11,607
Re: The Recent F/stop Controversy

Pixel Pooper wrote:

Michael Fryd wrote:

threw the lens wrote:

...

It's not worth creating an alternative to the f-stop, because people would still run into a conceptual brick wall later when they find that a 35mm f1.4 does not have the same depth of field as a 105mm f1.4.

...

One is not creating an "alternative to f/stops". The underlying optical property we are talking about is the diameter of the entrance pupil of the lens. "F/stop" is the alternative that we use when we are more concerned about light per unit area than exposure.

How can you be more concerned about light per area than exposure, when exposure is light per area by definition?

Sorry. I mistyped. I meant to say:

One is not creating an "alternative to f/stops". The underlying optical property we are talking about is the diameter of the entrance pupil of the lens. "F/stop" is the alternative that we use when we are more concerned about light per unit area than total light captured.

Thanks for catching my mistake.

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kiwi2
kiwi2 Veteran Member • Posts: 4,620
Re: The Recent F/stop Controversy
1

Michael Fryd wrote;

I would say that for digital photographers the actual aperture diameter is more important than the ratio of focal length to diameter.

Nonsense.

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Michael Fryd
Michael Fryd Forum Pro • Posts: 11,607
Re: The Recent F/stop Controversy
1

kiwi2 wrote:

Michael Fryd wrote;

I would say that for digital photographers the actual aperture diameter is more important than the ratio of focal length to diameter.

Nonsense.

Consider a digital photographer shooting raw and a film photographer.

Both have a camera/lens combination with a 40° angle of view.

Both have settings that result in an aperture diameter of 12.5mm.

Both have a shutter speed of 1/60 second.

Both are shooting the same subject, from the same spot, at the same time.

The digital photographer has no need to know the sensor size, focal length, or ISO value.  He can set the camera on AUTO-ISO and get a great result.

The film photographer doesn't have this option.  He needs to make sure that the intermediate step of light per unit area on the sensor falls into a specific range.

The digital photographer only needs to worry about total light.  The digital photographer gets essentially the same results independent of sensor size. Therefore the digital photographer does not need to be concerned (or even aware of) the ratio of focal length to aperture diameter.

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Aaron801 Veteran Member • Posts: 6,119
Re: Really?

Pixel Pooper wrote:

Michael Fryd wrote:

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.

This is the issue. You have built your workflow around "exposure" (light per unit area). While this makes sense for film it isn't necessary for digital.

You don't know what my workflow is.

When taking a photo we need to balance shutter speed (which affects motion blue), aperture (which affects depth of field) and total light (which affects image noise). When you have ample subject illumination, there will be a range of settings that give you the desired results.

The important situation is what happens when there isn't ample subject illumination? How do you balance the three elements?

If we start by picking one, then we have taken it out of consideration for balancing. If we set the camera to a fixed ISO (which selects a target exposure) and put the camera into shutter priority mode, then we are telling the camera to use aperture for balancing. This means that if there is more than ample illumination, we get more depth of field, and when there isn't enough then we don't get as much depth of field as we need.

If we move the camera to aperture priority, we run into the problem that not enough light give us motion blur.

By basing our workflow on exposure we tend to forget about our third choice. Set the aperture to give us the depth of field we need. Set the shutter speed to give us the motion stopping ability we want, and let the exposure fall where it may (Auto-ISO).

Auto ISO in M mode does not let the exposure fall where it may, it lets the ISO fall where it may. You chose the exposure when you set the aperture and shutter speed, and if you choose too high or too low an exposure, auto ISO will not be able to bail you out.

This third choice isn't a practical option with film, and our entire workflow and nomenclature is based on the need to hit the sweet spot on the response curve for film.

My workflow has nothing to do with the response curve for film.

====

If you have ever shot in aperture priority mode, then you have let the camera pick the shutter speed. If you have ever shot in shutter priority mode, then you have let the camera pick the aperture. What's so special about exposure? Why do we have to start by picking an exposure?

You seem confused. The workflow you described above using auto ISO in manual started with picking an exposure, then the camera chose the ISO based on that exposure.

====

A typical response is that the photographer needs to pick the exposure as he wants to control the noise in the image. The fallacy of this is that the photographer should also want to control the depth of field and motion stopping ability. All three are important.

That's not a fallacy. Your exposure settings control noise, DOF, and motion blur.

Building a workflow around exposure (light per unit area) is a holdover from film days. It was important then, but is an artifically imposed limitation with digital.

Exposure is not an artificially imposed limitation. If your exposure is to low you get noise, and if it is to high you get blown highlights. This is photography 101. You can't just ignore exposure.

You keep advocating a workflow based on aperture diameter and angle of view, but you haven't explained how that would work in practice. Please explain how you propose we take pictures without using exposure.

Good point! f-stop is useful for figuring out exposure, which is the same on any camera. You need to deal with exposure before anything else really, it's that basic. If you were say to have several cameras of different formats, the same rules of exposure would apply to each one and the same settings to get that same exposure. Sure, they will each handle noise differently, but that's not exposure and you don't really need ay kind of fancy jargon or a slide rule to figure that out. It's something that one can get a sense of when they use each camera. I have just one camera and I have a sense of how much noise I'm likely to get at any given ISO (which is also determined somewhat by light and subject)...

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Bill Ferris
Bill Ferris Veteran Member • Posts: 4,361
Re: The Recent F/stop Controversy

Michael Fryd wrote:

Bill Ferris wrote:

Michael Fryd wrote:

it's not so much a technical question as a philosophical one. Is the frame of reference designed for the limitations of film the best frame of reference to use for digital?

Perhaps, I am misreading your comment and question. It appears you consider f-stop to be more relevant to film than to digital. Or at the very least, you see f-stop as a concept or setting that may be more relevant to film than to digital. Is that accurate?

I would say that for digital photographers the actual aperture diameter is more important than the ratio of focal length to diameter.

Yes, if you know the focal length you can convert from one to the other. But I would say one is better off using the value that's relevant, rather than a related value.

As you and probably everybody participating in this discussion know, the focal ratio of a lens (aka f-stop, f/ratio) describes the ratio of the focal length of the lens to the diameter of the aperture of the lens. Both dimensions are typically measured in millimeters. For example, a 100mm lens with an aperture diameter of 25mm, is described as, f/4. That's the lens's f/ratio. It's the f-stop chosen by the photographer.

Correct.

The use of f-stop to describe the physical characteristics of a lens applies regardless of the light-sensitive medium used. Whether that medium is a chemical emulsion or a collection of pixels, f-stop has the same meaning. Also regardless of the light-sensitive medium used, f-stop along with scene brightness and shutter speed define exposure: the average brightness of the scene at the image plane. This is another fact of which you and most others in this thread are well-aware.

Correct.

But don't forget other implementation details that perhaps are more important that light per unit area. For instance number of photons hitting each pixel.

We tend not to talk about exposure in terms of photons per pixel because that's an implementation detail, and tells us very little about the final image unless we know how many pixels there are.

My point is that with digital, light per unit area (traditionally called "exposure") is an implementation detail, and tells us very little about the final image unless we know the area of the sensor.

On the other hand total light gathered tells us useful information about the final image without knowing the specifics of either the pixel or sensor size.

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.

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.

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.

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.

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.

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.

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.

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.

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Michael Fryd
Michael Fryd Forum Pro • Posts: 11,607
Re: Really?

Aaron801 wrote:

...

Good point! f-stop is useful for figuring out exposure, which is the same on any camera. You need to deal with exposure before anything else really, it's that basic. If you were say to have several cameras of different formats, the same rules of exposure would apply to each one and the same settings to get that same exposure. Sure, they will each handle noise differently, but that's not exposure and you don't really need ay kind of fancy jargon or a slide rule to figure that out. It's something that one can get a sense of when they use each camera. I have just one camera and I have a sense of how much noise I'm likely to get at any given ISO (which is also determined somewhat by light and subject)...

I disagree with your assertion that "You need to deal with exposure before anything else really, it's that basic".

That was true for film, but is not for digital.

Why is it more important to deal with exposure before dealing with aperture or shutter speed?   With film the answer was that if you didn't hit the target exposure that matched your film, nothing else mattered.

With digital, there is a wide range of exposures that produce good results.

====

The other issue, is that with film, it's the light per unit area that affects your results.  With digital it's the total light captured.

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tony field Forum Pro • Posts: 10,295
Re: The Recent F/stop Controversy
2

Michael Fryd wrote:

kiwi2 wrote:

Michael Fryd wrote;

I would say that for digital photographers the actual aperture diameter is more important than the ratio of focal length to diameter.

Nonsense.

Consider a digital photographer shooting raw and a film photographer.

Both have a camera/lens combination with a 40° angle of view.

Both have settings that result in an aperture diameter of 12.5mm.

Both have a shutter speed of 1/60 second.

Both are shooting the same subject, from the same spot, at the same time.

The digital photographer has no need to know the sensor size, focal length, or ISO value. He can set the camera on AUTO-ISO and get a great result.

The film photographer doesn't have this option. He needs to make sure that the intermediate step of light per unit area on the sensor falls into a specific range.

The digital photographer only needs to worry about total light. The digital photographer gets essentially the same results independent of sensor size. Therefore the digital photographer does not need to be concerned (or even aware of) the ratio of focal length to aperture diameter.

You almost seems to be advocating that cameras need have only a "total light meter" that really would be a surrogate for image quality. Iso then becomes a brightness control.

It seems to me that too much emphasis on total light only complicates photography unnecessarily in spite of the fact that it is an extremely useful concept for a photographer to understand and know how to control.

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mamallama
mamallama Forum Pro • Posts: 56,106
Re: Really?
1

Michael Fryd wrote:

Aaron801 wrote:

...

Good point! f-stop is useful for figuring out exposure, which is the same on any camera. You need to deal with exposure before anything else really, it's that basic. If you were say to have several cameras of different formats, the same rules of exposure would apply to each one and the same settings to get that same exposure. Sure, they will each handle noise differently, but that's not exposure and you don't really need ay kind of fancy jargon or a slide rule to figure that out. It's something that one can get a sense of when they use each camera. I have just one camera and I have a sense of how much noise I'm likely to get at any given ISO (which is also determined somewhat by light and subject)...

I disagree with your assertion that "You need to deal with exposure before anything else really, it's that basic".

That was true for film, but is not for digital.

Why is it more important to deal with exposure before dealing with aperture or shutter speed?

By all accounts I always thought of aperture and shutter speed as being exposure. What are you talking about? You seem to be making circular arguments.

With film the answer was that if you didn't hit the target exposure that matched your film, nothing else mattered.

With digital, there is a wide range of exposures that produce good results.

====

The other issue, is that with film, it's the light per unit area that affects your results. With digital it's the total light captured.

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tony field Forum Pro • Posts: 10,295
Re: Really?

Michael Fryd wrote:

Aaron801 wrote:

...

Good point! f-stop is useful for figuring out exposure, which is the same on any camera. You need to deal with exposure before anything else really, it's that basic. If you were say to have several cameras of different formats, the same rules of exposure would apply to each one and the same settings to get that same exposure. Sure, they will each handle noise differently, but that's not exposure and you don't really need ay kind of fancy jargon or a slide rule to figure that out. It's something that one can get a sense of when they use each camera. I have just one camera and I have a sense of how much noise I'm likely to get at any given ISO (which is also determined somewhat by light and subject)...

I disagree with your assertion that "You need to deal with exposure before anything else really, it's that basic".

That was true for film, but is not for digital.

If we assume we are using a camera with a light meter or equivalent, the very first thing we always did was choose the iso of the film to be used. This is established the exposure that would be considered appropriate. The only option for variable ISO was to have multiple cameras or multiple film backs with appropriate ISO selection in each.

In a sufficiently useful definition, ISO for digital and film is respectively the same: for a given light meter reading the output image should be brightened according to ISO standards to represent an 18% gray appropriately.

Why is it more important to deal with exposure before dealing with aperture or shutter speed? With film the answer was that if you didn't hit the target exposure that matched your film, nothing else mattered.

With digital, there is a wide range of exposures that produce good results.

For a given ISO or even auto ISO only a single exposure is appropriate.

The only real advantage of digital is that you have "many interchangeable backs of film" available in the digital camera firmware.

====

The other issue, is that with film, it's the light per unit area that affects your results. With digital it's the total light captured.

film systems responded the same way as total light on digital. You chose a larger format camera to achieve more total light or alter the ISO in your film holder.

With both film and digital systems, a single format camera only has limited ability to alter total light based upon ISO.

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Aaron801 Veteran Member • Posts: 6,119
Re: Really?

Michael Fryd wrote:

Aaron801 wrote:

...

Good point! f-stop is useful for figuring out exposure, which is the same on any camera. You need to deal with exposure before anything else really, it's that basic. If you were say to have several cameras of different formats, the same rules of exposure would apply to each one and the same settings to get that same exposure. Sure, they will each handle noise differently, but that's not exposure and you don't really need ay kind of fancy jargon or a slide rule to figure that out. It's something that one can get a sense of when they use each camera. I have just one camera and I have a sense of how much noise I'm likely to get at any given ISO (which is also determined somewhat by light and subject)...

I disagree with your assertion that "You need to deal with exposure before anything else really, it's that basic".

That was true for film, but is not for digital.

Why is it more important to deal with exposure before dealing with aperture or shutter speed? With film the answer was that if you didn't hit the target exposure that matched your film, nothing else mattered.

With digital, there is a wide range of exposures that produce good results.

The same could be said for film! With both film and digital you can get a variety of effects of course if you deviate one way or another from the exposure that your meter gives you. Knowing when to over or under expose is the same for film or digital. Of course some of that you can control in post production, but that's kind of similar with both mediums. With film you had to worry more about shadow detail as you could only pull up the shadows so much and with digital you have to worry more about blowing highlights... so it isn't as if either one has anything like endless latitude.

I can't see that film and digital are that much different in the respect that the first thing that you need to learn with either is the exposure triangle. F stop then is useful as a variable in this triangle, no matter which medium you're using or what format... Simple as that.

====

The other issue, is that with film, it's the light per unit area that affects your results. With digital it's the total light captured.

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Great Bustard Forum Pro • Posts: 43,015
So long as motion in the scene or of the camera...

RUcrAZ wrote:

A great deal of these postings are null and unimportant, when one considers something called "exposure bracketing."

(Nearly every post (didn't read them all) is "correct," but they are not very critical -within limits, not "outer fringe conditions"- to the fact that you can usually have your cake and eat it by exposure bracketing.)

...does not adversely affect the photo, absolutely.  Same applies to noise (stacking) and resolution (stitching), too.

Michael Fryd
Michael Fryd Forum Pro • Posts: 11,607
Re: The Recent F/stop Controversy
1

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.    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.

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.

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.

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

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.

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

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.

Aperture diameter and angle of view inform us on the subject of depth of field and subject framing.

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.

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.

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.

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Michael Fryd Forum Pro • Posts: 11,607
Re: The Recent F/stop Controversy

tony field wrote:

...

You almost seems to be advocating that cameras need have only a "total light meter" that really would be a surrogate for image quality. Iso then becomes a brightness control.

Yes.

ISO is already a brightness control.  The difference is that is is labeled based on light per unit area. I think we would be better off with something labeled based on total light captured.

Some people call this "effective ISO".  For instance ISO 100 on a 2X crop body is "effective ISO 400" because it captures about the same amount of light as an ISO 400 exposure on a full frame body.

It seems to me that too much emphasis on total light only complicates photography unnecessarily in spite of the fact that it is an extremely useful concept for a photographer to understand and know how to control.

A simple explanation may seem complicated at first if you are used to a complicated explanation.

There is little reason for a beginner using a digital camera to be concerned about light per unit area on the sensor.  Explaining the process in terms of aperture diameter, and total light captured really is a simple explanation.

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kiwi2
kiwi2 Veteran Member • Posts: 4,620
Re: The Recent F/stop Controversy
2

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..?

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Great Bustard Forum Pro • Posts: 43,015
Re: The Recent F/stop Controversy
2

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.

kiwi2
kiwi2 Veteran Member • Posts: 4,620
Re: It's weird, isn't it?
2

Michael Fryd wrote:

kiwi2 wrote:

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

With that particular example neither shutter speed, nor aperture are critical, and there is more than enough subject illumination to get sufficient total light for an acceptable level of image noise. In this situation, the camera settings aren't important at all.

The fact that there are some situations where camera settings are not critical does not mean that this is true for all situations.

I also like to shoot that view off the back doorstep in low light too...

But I still don't worry about equivalence with some other randomly chosen camera.

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tony field Forum Pro • Posts: 10,295
Re: The Recent F/stop Controversy

Michael Fryd wrote:

tony field wrote:

...

You almost seems to be advocating that cameras need have only a "total light meter" that really would be a surrogate for image quality. Iso then becomes a brightness control.

Yes.

ISO is already a brightness control. The difference is that is is labeled based on light per unit area. I think we would be better off with something labeled based on total light captured.

Does not the iso value already define the total light to be captured for your particular camera sensor?

Some people call this "effective ISO". For instance ISO 100 on a 2X crop body is "effective ISO 400" because it captures about the same amount of light as an ISO 400 exposure on a full frame body.

That is a complete misuse of equivalence. Correct numbers do not mean correct description.

It seems to me that too much emphasis on total light only complicates photography unnecessarily in spite of the fact that it is an extremely useful concept for a photographer to understand and know how to control.

A simple explanation may seem complicated at first if you are used to a complicated explanation.

I have never seen a good simple explanation becoming complicated except when somebody over explains it.

There is little reason for a beginner using a digital camera to be concerned about light per unit area on the sensor. Explaining the process in terms of aperture diameter, and total light captured really is a simple explanation.

it all depends upon what you are trying to explain.

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LoneTree1 Senior Member • Posts: 1,315
Re: refrains and concerns?

MediaArchivist wrote:

LoneTree1 wrote:

What is the biggest refrain of people with kit lenses? "Darn, I could do with a few fewer mm's at the wide end."

I'm not sure that is true.

What is the biggest concern of people with tele-zooms? "Why do I need 70mm when I shoot mostly 300mm and why is the long end always the "worst" optically?

300mm primes are pretty expensive, for a reason. How does that affect the common measurements of relative apertures?

Cheaper 70-300mm zooms top out at f/5.6 while the prime can be as fast as f/2.8.  However, a 300mm f/4.0 lens from some manufacturers isn't that much more than a good 70-300mm, is one stop faster and likely, better-built with noticeably better optics.

Bill Ferris
Bill Ferris Veteran Member • Posts: 4,361
Re: The Recent F/stop Controversy
1

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.

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.

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.

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.

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.

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?

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.

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.

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?

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.

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

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.

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.

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?

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