Aperture - Equivalence or Equivalency?

finnan
April 1, 2024
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    Team
    April 11, 2024, 8:12 p.m.
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    That last bit is the thing. Equivalence is all about making photos that look the same (on the basis that a photographer has some intention about how the photo should look). The look of a photo, in terms of motion blur imbued by a particular exposure time, doesn't change with frame size. The look, in terms of DOF at a selected f-number does change, meaning that you'd have to change the f-number to get the desired DoF with a different size sensor. Likewise the look in terms of AoV for a given FL does change, so if you want a particular AoV you have to change FL with sensor size.
    The ISO thing is simply because, as you say, changing the f-number with the same shutter speed and scene illuminance changes the exposure, so if you want the photo rendered with an intended lightness you'll need to change the ISO.

    The question that raises is why is exposure important? This is a genuine question, but when I ask it I tend to get answers such as 'if you don't even know that, there's no point even discussing with you'.

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    Team
    April 11, 2024, 8:28 p.m.
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    Assuming that exposure means total light/photons collected [per unit sensor area], then it better has to be optimal to use most of available sensor dynamic range and not to cause saturation. Sure for nowadays cameras with broad ISO range and software tools with AI correct exposure is not that important than in old film times (or even not so old Sigma/Foveon camera times :)).

    At least that is what I'm thinking - surely many people here will teach me other views :)

    Of course importance of exposure (or lack of it) is not directly related to fact that it depends on F/number, not some equivalent thing.

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    Team
    April 11, 2024, 8:44 p.m.
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    OK, when expressed this way, I can understand it.

    What my internal language filter objects (this may be related to me being non-english) is that statement 'to get equivalent image we have to adjust shooting parameters according to sensor size' (which I don't oppose at all) is replaced with statements 'parameter X value A is equivalent to value B on other system' - because the latest statements are not correct by itself, IMO.

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    Team
    April 11, 2024, 8:52 p.m.
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    But that means that it is 'total light' rather than exposure that is important, no?

    The development of the concepts of f-number and exposure when hand in hand. In the early days 'exposure' meant just the exposure time. Photographers would say things like 'with this emulsion and a 12-inch lens with a 1-inch aperture an exposure of 12 seconds in sunlight is about right'. The the reciprocity principal was discovered, and they'd find out that if you used a 2-inch aperture on your 12-inch lens you could do with six seconds. Annoyingly, the aperture needed depended on the length of the lens, so people started using relative apertures, which in the end settled down to the f-number. With that in place the word 'exposure' came to mean a combination of exposure time, f-number and scene luminance - formalised by Hurter and Driffield in their sensitometric work.

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    Team
    April 11, 2024, 8:54 p.m.
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    It's this bit about photographer's intention that seems to be the sticking point. This is going to sound elitist, but I get the impression that many photographers' intention stops at getting the lightness they want.

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    Members 695 posts
    April 11, 2024, 10:32 p.m.
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    I would phrase it differently: Equivalence isn't about making photos that look the same; rather, it's about the settings on different formats that result in photos where certain important visual qualities (perspective, framing, DOF, and motion blur) are all the same. From there, we can see if one format or the other offers advantages with regards to these (and other) properties that are preferable for our photography, with regards to equipment choices. Obviously, if one system can get us a better photo than another system can by not using Equivalent settings, we would certainly do so.

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    Members 549 posts
    April 11, 2024, 11:57 p.m.
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    That's not exposure. Exposure is what the lens projects toward the sensor. Much of that light never gets detected.

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    Members 695 posts
    April 12, 2024, 12:15 a.m.
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    That's a fair distinction to make, especially when comparing newer cameras to older cameras. For example, let's say we shot the same scene with the ["ancient"] Canon 5D and the modern Canon R5 at f/4 1/400, both using the same lens. The exposure will be the same for both, but the recorded exposure will be twice as high for the R5, as the more modern sensor records twice as much light projected on it as the older 5D.

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    Members 2365 posts
    April 12, 2024, 4:58 a.m.
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    turn up DRO on sony or shoot slog 3 and its a total different ball game to expressing lightness.

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    Members 562 posts
    April 12, 2024, 6:45 a.m.
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    Wow! That TOP article really hit a nerve!

    I did not expect it to be taken so seriously; it seemed to me to be largely satirical and very much his personal opinion (as is most of TOP's content), not something to get worked up over.

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    Members 695 posts
    April 12, 2024, 4:42 p.m.
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    No, the article was not "largely satirical", not by a long shot:

    This will probably annoy a few people, but I'm sorry, I think it's true, even if it's not true of you. I personally think the equivalent aperture fallacy mainly exists because it relates to status and prestige. It's usefulness for many (not all) of those who promulgate it is in asserting that one can achieve shallower DoF with a "full-frame" (FF) camera than others can using smaller-sensor cameras even if the latter have the same speed or slightly faster lenses. ("My FF Ζ’/1.4 lens is better than your Micro 4/3 Ζ’/1.2 lens.") At root it's a way of showing off a claimant's ownership of expensive equipment, and there's not really much more to it than that.

    That is absolutely not sarcasm, nor is anything else in the article.

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    Team
    April 12, 2024, 5:01 p.m.
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    Well, this was real bad wording from my side. I meant 'collected' as 'fallen onto sensor area', not 'converted into measurable charge'.

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    Team
    April 12, 2024, 5:12 p.m.
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    Both :)
    Total light corresponds to total informational content, exposure as 'light per unit area' is related to sensitivity (of film or photodiodes or whatever detects photons), consequently it affects sensor design and similar things.
    I would not start any argument about those topics - this could open another can of worms.

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    Members 184 posts
    April 13, 2024, 12:39 a.m.
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    Another article from the TOP website was cited over on DPR which has sparked up the weekly equivalence debate:
    www.dpreview.com/forums/post/67647242

    Quite entertaining. Jim Sterling and I have been batting it back and surprisingly, the thread hasn't been locked, yet!

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    Members 695 posts
    April 13, 2024, 1:45 a.m.
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    I'm afraid I'm confused -- Tom Caldwell has assured me numerous times that everyone already understands Equivalence (therefore, I don't need to keep posting "corrections" to misunderstandings and misrepresentations, even sandboxing me to save me the trouble), yet the article makes the claim:

    3. Focal Lengths Have Equivalents, Apertures Don't
    ...
    What is not correct is to claim that this Ζ’/1.7 lens is the equivalent of a full-frame 150mm Ζ’/3.5 lens! There is a technical term for thatβ€”"utter nonsense."

    So, is Ctein being "sarcastic" again? 😁

    By the way, you quoted a great rebuttal in your reply!

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    Members 184 posts
    April 13, 2024, 5:35 a.m.
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    Well, I am glad to find support from those who are well versed, and often go back to your excellent essay to obtain good source material!

    As for the m4/3 forum, it is one long conga-line of equivalence denialists.

    Here's another recent thread that went right off the rails:
    www.dpreview.com/forums/post/67644821

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    Members 1963 posts
    April 13, 2024, 6:58 a.m.
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    The attacks on Hogan are more amusing. I never see threads started to attack him on the Nikon forums. He goes down very hard on Nikon regularly.

    I do not get, or maybe I do, this brand loyalty, that we see on many forums. When I felt Nikon were slipping downhill with the quality of their products, I had no problems switching to Olympus/Panasonic, using the best bits of both brands. One gets sucked into the fanboy syndrome a bit, but when I picked up a Nikon Z7, I had no problems trading in my M43 gear. I get upset too when some fanboy who uses another brand tells me that what I am using is junk.

    Equivalence denial is just a symptom. The real problem is that a vocal group M43 users on that forum have an inferiority complex regarding the gear they use, and feel their choices need defending against the "big boys".

    It might just be better to post pictures showing that you can take great pictures with that still very valid system

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    Members 184 posts
    April 13, 2024, 8:27 a.m.
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    Yes, the level of defensiveness there is quite extreme.

    You're right of course. And I do that (post photos) over on L-mount-forum.com. I don't post photos on the m4/3 forum because if they are not birds in flight taken with an OM camera, there is nil interest.

    I just haven't quite weaned myself off the m4/3 forum because it's a circus and I can't help but reply. I expect that it will be forced soon when I join the ranks of those who have been banned.