The Recent F/stop Controversy

Started 1 month ago | Discussions thread
Bill Ferris
Bill Ferris Veteran Member • Posts: 4,090
Re: The Recent F/stop Controversy

Michael Fryd wrote:

Bill Ferris wrote:

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

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

Before going further, let's remind ourselves that the exact same factors that determine exposure for film media also determine exposure for pixel-based, light-sensitive media. Those factors work the same way. Everything from aperture diameter to zoom range applies the same for digital as it does for film.

Also, let's establish that it's in your interest to demonstrate real, tangible benefits to photographers who adopt your proposal. In the absence of any real benefits, there is no incentive to change the systematic approach to photography that has worked for generations and still works, today.

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

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

In photojournalism, there used to be a popular saying, "F/8 and be there." Perhaps, some version of that is still in use? I don't know. I mention this to illustrate thay photographers have prioritized creative settings ahead of sensitivity, since long before digital was a thing. Whether shooting landscapes, portraits or news, film photographers often choose an f-stop for a desired depth of field, a shutter speed to control the appearance of motion and are constantly on the lookout for films that allow improved print quality.

Adopting your proposal does nothing to change that or to make it any easier.

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

In many fundamental ways, a digital camera system does act like film. Optically, the same physics applied to lenses for film cameras are applied to digital cameras. Lenses designed in the film era are still used with digital cameras. It's well-established that scene brightness, shutter speed and f-stop determine exposure, both for film and digital. There's no need to beat that drum, any more.

Film ASA and digital ISO are not the same and this has been the catalyst for many an enjoyable & entertaining discussion in these forums.

Earlier, you described digital as producing a wider range of good quality exposures. Are you sure? One of the biggest advantages of digital over film, is that every possible ISO (or ASA, if one prefers) film stock is contained within the camera. The ability to select an ISO from 100 to 100,000 (or higher) effectively makes all film ASAs available, at any time.

By contrast, a film photographer can only have one roll of film in the camera at any one time. It's one reason professional photogs started carrying more than one camera. Not only was a second body a backup, it also allowed the photographer to have a roll of color negative film in one camera and a roll of Tri-X 400 in a second body.

Film allows one to use ASAs from about 60 to 6400 to make quality exposures and prints. That's at least a seven stop range. Film is inherently better than digital at preserving and allowing recovery of detail in highlights. That's another few stops, at least. Digital has an inherent advantage at recovering detail in shadows so, one can use ISOs higher than 6400; in some cases much higher.

Ultimately, both media offer a wide latitude of usable exposures. In both media, the same settings and controls for exposure can be applied to make great images.

Again, we return to the fundamental question of what real-world benefits await those who adopt the change you propose? What photograph will I be able to make that I'm not presently able to make? What task becomes significantly easier?

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

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

If the photo you're making doesn't suffer from f/4, 1/60, ISO 400, those settings will deliver a good exposure and a good image. If you desire a certain depth of field or wish to use a shutter speed that freezes motion to a certain degree, use the settings that will deliver the image you desire with the equipment you're using.

This is all totally achievable, today, without adopting the change you propose.

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

If your backup film body is loaded with ASA 1600 film, which exposure settings would you use?

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

What real world differences are we talking about, here? If your crop body can't make clean images at ISO 400, maybe you should replace it. If the diffraction effects of your lens are unacceptable at f/4, you should definitely replace it.

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

What if that's not possible? If you only have the f/4 lens and it doesn't open to f/2, what would you do? My guess is thay you'd find a way to make a good photo. It wouldn't be equivalent to the image you were going to make with the other camera but, frankly, that's only a minor detail. I shoot with full-frame, APS-C and smartphone systems, not because they're equivalent, but precisely because they are different. And some of those differences translate to advantages.

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

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

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

I can honestly say I've never had to calculate the aperture diameter of a lens to achieve a photograph I wanted to make. I suspect the same can be said of most photographers. For me and others, a camera that calculates and displays a setting I never use offers no advantage over a camera that does not calculate and display the same setting.

Assume you move closer to your subject and change the focal length to maintain the same framing. If the aperture diameter remains the

That is incorrect. If you move nearer the subject while maintaining the same aperture diameter and angle of view, apparent depth of field will be reduced. It will be shallower. Here, are two photos illustrating this:

Photo 1: 55mm, f/6.4, distance to subject is 4-feet, aperture diameter is 8.6mm

Photo 2: 27.7mm, f/3.2, distance to subject is 2-feet, aperture diameter is 8. 6mm

Notice the out of focus appearance of the trophy and tiles above the fireplace. The depth of field appears shallower due to the background elements looking obviously softer in focus. This change in appearance is due to the same approximately 8.6mm aperture diameter being used to photograph the background elements from a nearer distance.

By the way, I erred earlier when I said I've never calculated an aperture diameter to make a photo. I calculated the aperture diameters used for these photos.

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.

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

While digital cameras come with an almost inexhaustible supply of ISOs they come with just one sensor. Once you're committed to using a camera, there is no option to select a larger sensor. As we know, maximizing exposure for a scene also maximizes the volume of light which can be captured in a single exposure of that scene.

As I wrote in the previous reply, 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.

And if you're genuinely concerned about not capturing enough light from any area of the composition in a single exposure, there is sometimes the option of making and combining multiple exposures into a single image.

There is no need to calculate a specific amount of noise. There is only the need to know how to use shutter speed and f-stop to control exposure, the ability to interpret a histogram and a willingness to look at a photograph I've made and say, "Not good enough. I need to increase exposure to reduce noise."

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

If your smartphone doesn't make an acceptable photograph of a scene at those settings, use different settings or a different camera.

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

Exposure, alone, is enough to determine of you're capturing as much light as possible from a scene within the constraints of your chosen creative settings constraints. If the shot noise is objectionable, use a different camera with a larger sensor or make a different photo.

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

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

I don't calculate the actual depth of field because that information is not needed to make a good photo. All I need to know is that changing the distance to the subject (while keeping focal length and f-stop constant) changes depth of field. Being nearer produces a shallower depth of field and being more distant creates a deeper depth of field. Alternatively, I can maintain subject distance & footbal length and adjust f-stop (smaller/faster = shallower, larger/slower = deeper) to control depth of field.

I can rely on my experience as a photographer to make adjustments for the various subjects, backgrounds and lighting situations I encounter. There's also the option of choosing a different perspective offering a more pleasing background.

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

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

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

On this point, I and the vast majority of photographers will respectfully disagree. We don't calculate aperture diameter or the total light captured. Not having this information does nothing to limit our ability to make good photographs.

Benefits include:

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

You've demonstrated neither.

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

Light, is the priority. In the absence of light, all else is irrelevant.

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

Exposure is independent of sensor size. Total light captured is dependent on sensor size.

Michael, if the change you propose had real potential to deliver tangible benefits to photographers, I'd be standing shoulder-to- shoulder with you advocating for change. However, you've not made a persuasive case for any benefit from this change. From where I stand, it appears to be change for change's sake.

Clearly, you believe this change is needed. I would encourage you to dig deep in search of a real, tangible benefit. If you can demonstrate that adopting this perspective will make some type of photography either doable or much easier, others will come on board. But if it remains essentially a battle of archaic concepts, nobody's gonna get on your bandwagon.

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Flagstaff, AZ

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