The Recent F/stop Controversy

Started 2 months ago | Discussions
fferreres Senior Member • Posts: 1,890
Re: Yep, that's the modern world, all right.
1

Great Bustard wrote:

[Photographic] Equivalence is a paradigm that relates the visual properties of photos of a given scene from different formats based on perspective, framing, and the diameter of the [effective] aperture.

I have an alternative definition:

Photographic equivalence provides some rules of thumb to assess how a shot in certain format could have been shot in a different one and still look quite the same.

fferreres Senior Member • Posts: 1,890
Re: The Recent F/stop Controversy

Michael Fryd wrote:

"F/stop" is the alternative that we use when we are more concerned about light per unit area than exposure.

Can you help clarify what inches or mm would a barrel (or wheel in the camera) have? Would a 50mm and 52mm and 55mm now all have different apertures numbers even when they all have the same aperture in relation to FL?

I care about the concept of doubling and halving total light as opposed to thinking in terms of diameter of triangles, squares or pentagons, but what are you actually proposing in practice?

fferreres Senior Member • Posts: 1,890
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?

Honestly, I have been wondering the same for 4 threads already.

mamallama
mamallama Forum Pro • Posts: 55,868
Re: Yep, that's the modern world, all right.

Great Bustard wrote:

mamallama wrote:

Great Bustard wrote:

mamallama wrote:

Great Bustard wrote:

mamallama wrote:

I love the clarity when just the mention of equivalence results in multiple threads that limit out at 150. A concise one sentence definition of equivalence might help the clarity.

If you can't say it all in a Twitter post, then it isn't worth saying -- that's the world we now live in. Maybe if I ask the POTUS, he can do it just for you.

Now I know why it isn't worth saying.

Well, you were the one asking for the Twitter post version to get some clarity. So the three bullet points I gave:

  • For a given exposure, more light is projected on a larger sensor.
  • For a given scene, DOF, and exposure time, the same amount of light is projected on all sensors, regardless of size.
  • Thus, the only way for a larger sensor to collect more light is to use a more shallow DOF or longer exposure time.

were too much of a chore for you -- you wanted a "concise one sentence definition of equivalence" in order to have "clarity", but now say that a one sentence definition isn't worth saying because it reflects the same mindset of someone whose politics you don't like. Oh well -- can't please them all, I suppose.

Sorry, that is not a one sentence definition.

No kidding -- I said that my three bullet points "were too much of a chore for you" because you wanted a single sentence. But when I noted that the POTUS is the king of single sentence explanations, you said, "Now I know why it isn't worth saying". But, if you must have a single sentence, here it is:

[Photographic] Equivalence is a paradigm that relates the visual properties of photos of a given scene from different formats based on perspective, framing, and the diameter of the [effective] aperture.

At least we know you are thinking of it as a paradigm.  The description of the paradigm is rather vague, however.

.

Go back and read what I asked for.

There's your single sentence and is no more or less helpful in understanding what Equivalence is about than, say, a single sentence definition of Capitalism:

an economic system characterized by private or corporate ownership of capital goods, by investments that are determined by private decision, and by prices, production, and the distribution of goods that are determined mainly by competition in a free market

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fferreres Senior Member • Posts: 1,890
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.

You stated it so many times. We get your point of view and belief. I don't think anybody trying to follow you has missed you make this point over and over.

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.

If you state that one would say one is better using the value that's relevant, you are stating that the use of f-stop is irrelevant for everyone. You are generalizing to everyone, not just to your case and workflow.

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.

Exactly. We tend to not talk about exposure as photons per pixel, or mm apertures, because those are implementation details. We care about exposure, regardless of medium.

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.

Wrong.

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.

It doesn't "tells us"...maybe it "tells you". I want to make sure I am at ISO 100, or whatever is the optimum exposure amount, not less or more. I don't want everyone to care, but if they want the least amount of noise, and not having clipped outputs, I'd advise anyone to care a bit more. However, they all know this already.

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.

Apertures have been described this way even in most all applications that do NOT involve film at all. Actually, many of these application that do not involve any kind of light recording mechanism. And many of these, do not even involve exposure, light intensity or anything of sorts. They are describing a lens property, regardless of the scale at which the lens is built.

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

I think it describes a lens property. You may be having a projector, where there is no light sensitive medium. Using a specific metric to designate the aperture, will tell you something only in relation to the scale of such lens. If I shrink the lens proportionally, the f-stop doesn't change But the max aperture diameter will.

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.

So you are proposing Auto-ISO, and that this detail be hidden as an implementation detail that the user should care about. This follows immediately from what you are saying, and have repeated many times already. Why? In you statement, because now digital can operate in other ISOs where as film was limited to a certain ISO unless you wanted to change the film.

However, "we are not better off". Maybe you are better off. I don't want the camera you are describing.

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.

You have the opportunity. In my system, I don't need to elevate DOF any further. It's very very high and having mm designated apertures would make it very difficult for me to know if the aperture is staying the same in relation to the focal length when using a zoom, to name 1 out of 250 examples. I don't want the opportunity that my constant aperture 24-105L f/4 now is designated with a variable mm.

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.

No. Maybe it changes for you and some others. I still want to know the intensity of light, the ISO, the exposure and be able to control it by doubling it and halving it.

JDC1958 Senior Member • Posts: 1,223
Re: The Recent F/stop Controversy

Gerry Winterbourne 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.

f-stop is hardly technical at all: a wider aperture lets in more light, but for a longer lens takes light from a smaller area of the illuminated subject. So for a given exposure a longer lens needs a physically wider aperture. As the widening of the aperture is proportional to the extra (focal) length then it makes sense - and makes setting exposure very much easier - if the aperture is expressed as a proportion of focal length. That's all f-stop is; it would take some searching to find anything less technical.

Oh, and a wider aperture gives shallower depth of field so that, too, is most easily expressed by reference to f-stop.

I think that too many photographers become so embroiled in the technical aspects that they forget that photography is more about being creative .

Actually, too many photographers forget that without the technicalities there would be no cameras and nothing to be creative with. What's the point of creativity if your pictures are badly exposed and/or are blurred out of recognition because you didn't get depth of field right?

I suppose it's theoretically possible for someone to get too embroiled but in 60+ years of photography I've never met any.

Such a simple thing takes 125 responses to explain in this thread and the last one went the 150 max limit. Are there really some people here that thick?

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fferreres Senior Member • Posts: 1,890
Re: The Recent F/stop Controversy

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.

No, one of them will have 12.5 and the other, on a 1/2" sensor is now wondering where is the 12.5mm setting or that it's stuck at 5mm.

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

Then, they must be the same person.

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.

So both could now be at ISO 125000 and they should not know about it.

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 film photographer will know exactly what's going on, unlike you hypothetical digital photographer.

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.

Your hypothetical photographer can't know the total light unless you provide a way to know exactly the ambient light, and would need to guess if that ISO will have a lot of noise or not, and then will have to mentally assess how much to trade off shutter or "aperture mm...how many??" to get it to a decent number that will not result in a washed out, all noisy and unacceptable output.

fferreres Senior Member • Posts: 1,890
Re: Really?

Michael Fryd wrote:

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

Half the light, twice the noise (rule of thumb of course). Maybe the problem is you don't understand or maybe do not care (or mind) about noise and its role in producing good results.

Do you not see how inconsistent you are when you state we should only care about the total light, but not when the sensor may be receiving 1/2 the light it needs, or 1/8, or twice as much, and that the photographer should even need to know about this?

JDC1958 Senior Member • Posts: 1,223
Re: Really?

fferreres wrote:

Michael Fryd wrote:

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

Half the light, twice the noise (rule of thumb of course). Maybe the problem is you don't understand or maybe do not care (or mind) about noise and its role in producing good results.

Do you not see how inconsistent you are when you state we should only care about the total light, but not when the sensor may be receiving 1/2 the light it needs, or 1/8, or twice as much, and that the photographer should even need to know about this?

Noise is not that big of a deal anymore. I still shoot film and I shoot digital. My little D500 at ISO 1600 is totally acceptable. When I had my full frame Pentax K1, ISO 3200 was totally acceptable. But then again, I don't make prints of 100% crops

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fferreres Senior Member • Posts: 1,890
Re: The Recent F/stop Controversy

Michael Fryd wrote:

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.

What I understand is that if you do the same framing at different FL, every f-stop you chose for both with have the same DOF. Nw, if I do the same framing with different FL, the same aperture diameter will NOT have the same DOF. As the FL changes, so does the DOF, even if you do the same composition. So DOF now changes for the same framing and you cannot know what is equivalent without a lot of extra effort.

That's because they provide the two factors you need to know in order to determine aperture diameter.

based on the number of responses, I'd argue "we" don't need to know aperture diameter. I think it's you that need to know it. You've stated it a hundred times literally the past week. I haven't read other than you maybe one or a few person in the entire forum say so.

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

That's so ever clear at least for you.

fferreres Senior Member • Posts: 1,890
Re: The Recent F/stop Controversy
1

Michael Fryd wrote:

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.

Are you proposing that labeling them according to the gear diameter (that will change car by car) as easier than 1, 2, 3 4 and 5? I even shared with you how we could label f-stops 0, 1, 2, 3, 4 in a way that totally makes sense (even if not better it's the same math).

fferreres Senior Member • Posts: 1,890
Re: Really?

LoneTree1 wrote:

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.

Most interesting fact in the thread. I suspected it but it was a guess as I haven’t had a friend or anyone introducing me to the topic.

fferreres Senior Member • Posts: 1,890
Re: Really?

LoneTree1 wrote:

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.

Except that 1900 lenses with apertures started clickless, and modern Zeiss gems in production today still carry clicks in camera models. Area is area but at least f-stop in metric agnostic and doesn’t pretend to convey a triangle is circle. But I agree with what you say too

tcg550 Veteran Member • Posts: 8,951
Re: The Recent F/stop Controversy

lanefAU wrote:

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

Where do you get your statistics?

golfhov Forum Pro • Posts: 10,487
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bolt2014 wrote:

The post about getting rid of the "F/stop" definition turned into such a technical subject

It was a "technical" subject.

that most photographers become lost in the jargon.

Uhhhhhhh that's what the conversation was about

I think that too many photographers become so embroiled in the technical aspects that they forget that photography is more about being creative .

This seems like a lot and kettle thing. The OP wanted to have a technical conversation and thinks the language needs changed.

If somebody DOESN'T want to have a technical conversation then they should stay out of it. There are PLENTY of photographers who are VERY good despite not having technical skills or understanding of terminology. The problem would be if we let them all come in and create their own language based on their ignorance of the subject, and then discussions would be impossible. We would spend all our time trying to figure out what the definition of the word they use is. If we all understand the terminology conveying ideas goes much faster. So whoever is using incorrect terminology could save 99% of us from wasting our time by just using the time it took to write their post to instead research the topic......

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Michael Fryd
Michael Fryd Forum Pro • Posts: 11,460
Re: The Recent F/stop Controversy

mamallama wrote:

...

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.

Don't worry.  Photographers have been using f/stops for years.  We're smart and can take great photos even when the equipment isn't helping us as much as it can.

It's quite possible to take great photos when you misunderstand the underlying technology.  As long as your mental model gives you reasonable guidance in your situation you're going to get good results.  However, if the mental model is wrong, it can give you bad advice in challenging situations.

The standard example is that higher ISO settings cause more image noise.   As a rule of thumb this works in common situations.  A wedding photographer could produce great results with this misunderstanding.

The problem is what happens in a difficult situation.  The photographer sees an opportunity for a fantastic shot, but his camera tells him he needs ISO 3200, and the photographer doesn't want that much noise.  His guideline is that the ISO setting causes the noise, to he makes sure his camera is set to capture raw, sets the ISO to 800, and plans to raise the brightness in post processing.  His mental model tells him this trick will decrease visible noise as he has selected a lower ISO.  In reality it won't help, and may increase visible noise.

As you understand more about the technology, you gain the ability to overcome more challenges.  However, with today's modern gear, you don't need to understand very much to shoot in easy situations.

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tbcass
tbcass Forum Pro • Posts: 43,210
Re: The Recent F/stop Controversy

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 .

Not true. There's no reason why we can't be creative and interested in the technology at the same time. Being disinterested in technology doesn't magically make you more creative. Many people that are technologically adept invent things. Invention is a highly creative process. At the same time many people who think they are creative in their photography aren't because all they are doing is recreating what they've seen other photographers do.

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Michael Fryd
Michael Fryd Forum Pro • Posts: 11,460
Re: Really?

fferreres wrote:

Michael Fryd wrote:

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

Half the light, twice the noise (rule of thumb of course). Maybe the problem is you don't understand or maybe do not care (or mind) about noise and its role in producing good results.

Do you not see how inconsistent you are when you state we should only care about the total light, but not when the sensor may be receiving 1/2 the light it needs, or 1/8, or twice as much, and that the photographer should even need to know about this?

  • Half the total light does result in more image noise.
  • Double the shutter duration and you get more motion blur.
  • Open the aperture up and you get less depth of field.

Each of which can affect the quality of the resulting image.

My point is that our nomenclature was designed to treat light per unit area as being paramount.    You will notice that this isn't one I listed.   In terms of noise it's total light gathered that's important.  In terms of depth of field, it's aperture diameter.

I am suggesting that workflow would be simpler, if our nomenclature and workflow was not based on the implementation detail of light per unit area.

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Michael Fryd
Michael Fryd Forum Pro • Posts: 11,460
Re: The Recent F/stop Controversy

fferreres wrote:

...

If you state that one would say one is better using the value that's relevant, you are stating that the use of f-stop is irrelevant for everyone. You are generalizing to everyone, not just to your case and workflow.

I am not stating it's irrelevant for everyone. I am stating that things are easier if you use a different framework for the discussion.

When explaining how things work we should talk about angle of view and aperture diameter.  There is no need to get into the specifics of sensor size or focal length.

Consider the following diagram.

Using the model of angle of view and aperture diameter, it is clear that both diagrams will produce the same results.

They have the same aperture diameter and same angle of view.  Therefore they capture the same total light.   It really doesn't matter whether the sensor is small and close to the lens, or larger and further from the lens.  That's an implementation detail.

However, if we teach f/stops, focal lengths,  ISO values, etc.,  it becomes difficult to explain why the above two produce about the same result.  After all the focal lengths, f/stops, and sensor sizes are all different.

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Gerry Winterbourne Forum Pro • Posts: 16,009
Re: The Recent F/stop Controversy

JDC1958 wrote:

Gerry Winterbourne 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.

f-stop is hardly technical at all: a wider aperture lets in more light, but for a longer lens takes light from a smaller area of the illuminated subject. So for a given exposure a longer lens needs a physically wider aperture. As the widening of the aperture is proportional to the extra (focal) length then it makes sense - and makes setting exposure very much easier - if the aperture is expressed as a proportion of focal length. That's all f-stop is; it would take some searching to find anything less technical.

Oh, and a wider aperture gives shallower depth of field so that, too, is most easily expressed by reference to f-stop.

I think that too many photographers become so embroiled in the technical aspects that they forget that photography is more about being creative .

Actually, too many photographers forget that without the technicalities there would be no cameras and nothing to be creative with. What's the point of creativity if your pictures are badly exposed and/or are blurred out of recognition because you didn't get depth of field right?

I suppose it's theoretically possible for someone to get too embroiled but in 60+ years of photography I've never met any.

Such a simple thing takes 125 responses to explain in this thread and the last one went the 150 max limit. Are there really some people here that thick?

No. Of the hundreds of posts in these threads almost none address the basic question of what f-stop (or f-number) actually is. Most of them digress either into arguments about equivalence (which uses f-stop but doesn't explain it) or into discussions about potential alternatives.

It's not that people in genera are too thick to understand f-stops; it's that a few can't resist hijacking the threads.

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