What Is Equivalence?

Agreed although I would say "about the same"; pardon the pedantry.

As in, if the crop factor was 1.5, then the ISO factor would be about 1.5^2 = 2.25.

Agreed. I wish we could get past the definition onto (what I find more interesting) subjects like, how do AVO/DOF/focus point change the visual appearance of a photo, because with the equivalent condition of view at the same size it certainly doesn't make photos wider! 😁 I really must be of to pack, or I'll be in the bad books...

Easily answered by most here, I would have thought.

For those in doubt: www.trenholm.org/hmmerk/TIAOOFe.pdf Caps 4 & 5 et subs.

Finished the packing, got a second or two, so...

I kinda meant the difference in say a focusing a portrait on the tip of a the nose against focus on the eye and the perceptual impression of overall sharpness that has on the finished photo for such a small change in focus point, and how that carries over to using focus in line with perception for other styles of photography, rather than a link to an article on the mathematical definition. But hey, if you run my response through equivalence I think you'll find it equally condescending... 😁😁😁😁

Actually, Equivalence applies equally to film or digital, available to buy or not.

The "broadly similar in performance" only relates to extensions of Equivalence, where Equivalence is typically applied to noise, DR, resolution, color, etc., but not applied to operation.

Because that's what Equivalence is all about -- the "performance envelope" of different formats with regards to the visual properties of photo (not elements of operation).

Equivalence does not create a "logical order based on the capabilities". It does limit itself to perspective, framing, DOF, motion blur, and, with proper assumptions about the specifics of the equipment, noise, DR, resolution, etc.. It absolutely does not say which tool is the "right tool" for any particular purpose or any particular person. However, it is easy to infer that if, for example, shallow DOF is something a photographer desires, then larger formats are typically (but not always) better suited for the job.

Again, Equivalence says absolutely nothing -- NOTHING -- about any of that. So you are attributing things to Equivalence that Equivalence says nothing about!

Exactly the opposite. "Orthogonal" means "independent to". So, Equivalence is the opposite of "orthogonal to facsimile" -- it tells you which settings on different formats result in facsimile (or the closest different systems can get, anyway). So, photos demonstrating the principles of Equivalence are necessarily photos of the same scene from the same position with the same [diagonal] angle of view displayed at the same size and in the same viewing conditions. But, I once again feel it is necessary to point out that purpose of Equivalence is in no way, shape, or form a mandate (or even suggestion!) to take Equivalent photos with different systems or make any statements, whatsoever, about the artistic merit of the resulting photos. Equivalence merely says that if you had used a different camera with Equivalent settings to take the photo you took with your camera, you would have gotten a photo with the same perspective, same [diagonal] framing, same DOF, same diffraction, and, with additional assumptions about the equipment, same noise, same DR, etc.. That's it. That's all Equivalence says. The rest of it is merely explaining why things are the way they are.

Again, you miss the absolute central premise of Equivalent photos: they must be photos of the same scene. I am certain I not only spelled that out before, but emphasized it more than a little strongly. Posting two photos of different scenes has absolutely nothing, whatsoever, to support or refute the principles or purposes of Equivalence. I'm not sure why you keep missing this central point. Let me restate from above, to make sure I am absolutely and unambiguously clear:

Equivalence merely says that IF you had used a different camera with Equivalent settings to take the photo you took with your camera, you would have gotten a photo with the same perspective, same [diagonal] framing, same DOF, same diffraction, and, with additional assumptions about the equipment, same noise, same DR, etc.. That's it. That's all Equivalence says. The rest of it is merely explaining why things are the way they are.

So, as soon as you post photos of different scenes in a comparison, you are no longer talking about Equivalence. At best, you could talk about elements of the photos using elements of Equivalence (but not Equivalence itself). For example, you could say that a photo would have looked better with more DOF. Then the photographer says something like, "Then I'd have to stop down and the photo would be too noisy or have too much motion blur, and I preferred the more shallow DOF as the lesser of evils". That's not Equivalence. It's discussing the aesthetics of a photo based on technical considerations that are discussed in Equivalence, but not Equivalence itself.

Perhaps this sounds contradictory, so let me explain a bit more. If you are talking about, say, DOF, well, DOF is a parameter of Equivalence. But that doesn't mean that you are talking about Equivalence when you talk about DOF. For example, let's say someone is asking if they should get a 135 / 1.8 or 70-200 / 2.8 for their camera. The discussion will involve angle of view, DOF, motion blur -- all elements of Equivalence -- as well as elements outside of Equivalence (e.g. size, weight, AF speed, etc.). But the discussion will not involve Equivalence itself. A discussion of Equivalence would be if, for example, someone were considering a 35-100 / 2.8 on mFT or 70-200 / 4 on FF. Then Equivalence becomes relevant.

So, to recap:

1) Equivalent photos are necessarily photos of the same scene. If the photos are of different scenes, then any comparison has nothing to do with Equivalence.
2) Equivalence is not about taking Equivalent photos on different systems: it's about if you used System A instead of System B and took a photo of that scene from the same position, then these settings would result in Equivalent photos, but System B could use these settings that System A has no Equivalent for, and that is worth considering if you are debating on switching to, or adding, System B.

That's pretty much it.

im using Chrome but does the same with Edge
Edit, it comes back after i posted this comment and remain on the page 🤨

And until you understand that unless you include the nature of perception in your discussion you're not talking about the visual properties of photos but only assuming you are...

And every single time you try to move past the definition of equivalence you get dragged right back. It's impossible to move the conversation beyond, and I've tried. I've tried to move beyond the mathematically equivalent photos and introduce human perception. My question was, if we move away from mathematically equivalent photos and include human perception, as in if we look at the actual photos we take with our cameras, doesn't that reduce the whole of equivalence to little more than a rule of thumb? But no photo is allowed in a discussion with equivalence in the title unless it conforms to the mathematical definition, no opinion is allowed unless it conforms to the mathematical definition of equivalence.

And this is the problem with equivalence, it's impossible to move a conversation beyond the definition. Here we are at post 112 and we're still at the basic definition. I get it, I do understand, I got it a fair few years ago. So why can't we move the conversation on, expand it a little, explore the topic, meander a little to see where it takes us?

This is so frustrating.

P.s. My bad about Orthogonal, my definition (I had to look it up) was "at 90 degrees to", so I assumed connected, an offshoot of.

Agreed, Arvo. One reason that the thread is now over 110 posts long is that, post-after-post-after-post, one member keeps trying to extend the thread discussion beyond what equivalence is to what it results in aesthetically.

I'm going to assume that we have established that Equivalent photos are photos of the same scene taken from the same position with the same focal point, same [diagonal] angle of view, same aperture diameter, and same exposure time, and that these photos are then displayed at the same size on the same media under the same viewing conditions, yes? If no, then we have to address that, so ignore the rest of this post.

That in place, are you saying that people viewing said photos may see differences in perspective, framing, DOF, and motion blur due to differences in human perception? If so, then we need to address that. If not, then we're actually done, 'cause that's all that Equivalence is saying. Anything more than that is something you are ascribing to Equivalence that Equivalence absolutely does not say.

Yes. And am I not alone in getting rather tired of it all?

I met a dead set Flat Earther once. Doesn't matter what you say, there is an answer for everything...

The technical aspects of photography was discussed about the differences between format sizes back in the film days, Print Grain Index, The very same with DOF calculations and enlargement. Funny as all of they are in the very root Equivalency.

I think this is too harsh and out of place. I'm thinking that Andrew is focused on Equivalence being about absolute properties of a photos as some sort of measure of their appeal as opposed to specific relative properties of two photos of the same scene, the purpose being a comparison of equipment as opposed to photographic technique. That is, when using the camera in hand, you don't use Equivalence. You use Equivalence when you are considering which camera to take with you or what equipment to buy. This is not to say, of course, that Equivalence is the whole of the decision process. But it would be part of the decision process. How much of a part would vary, of course, from individual to individual.

For example, Equivalence plays no role in discussing the relative merits between the following two photos:

What Equivalence does discuss is the merits of having taken the first photo with the camera used in the second photo or vice-versa. Now, of course, there are numerous factors that likely matter far more than the factors that Equivalence covers with respect to the photos above -- no one disputes this. Likewise, Equivalence says nothing about which of the two photos is "better". However, there are elements of Equivalence, as opposed to Equivalence itself, that would help in saying why different settings on the camera may have resulted in a "better" photo for either (e.g. use a lower exposure and process accordingly to reduce blown highlights). But this isn't Equivalence.

So, I think Andrew is honestly confused about what the hell Equivalence is all about if it doesn't help anyone take a better photo. If so, then I had thought I explained that Equivalence is a factor in choosing the equipment before the photo is taken, not about taking the photo once the equipment has been chosen, just as considerations such as acceleration, cornering, and braking might be considerations of what car one buys, but not considerations on how one uses it to go to work or go on a trip.

One might argue that the differences in equipment that Equivalence covers are all but moot with modern (and many not-so-modern) cameras and thus Equivalence plays no role in their personal decisions, whatsoever. Fair to say. But, if they were consistent, they would also say that the difference between an f/2.8 zoom and f/4 zoom, or the differences between an f/1.4 prime and f/2.8 prime, in terms of DOF options, noise, and sharpness (not in terms of size, weight, and cost!) are also moot.

Yes, there are the flat-Earthers, anti-vaxxers, and climate change deniers among the critics of Equivalence. However, I think it's unfair to pin this behavior on Andrew. There's something he's just not getting about the purpose of Equivalence, and that something might be so simple as to come to terms with the fact that Equivalence is exactly what it says and to take it at face value without reading anything more into it. And while that may be obvious to proponents of Equivalence, there are also those who misrepresent Equivalence to mean that larger formats are always better than smaller formats, and those people may instill confusion in others, the same way that "Communist" countries distort what Marxism is all about (not that I agree with Marxism, of course, but "Communist" countries are far, far, far from Marxist), the same way that "Christians" distort the message that Jesus tried to give (not that I agree with all that Jesus said, but the way "Christians" act is far, far, far from what Jesus preached), or the same way that cats can look and act so cute:

or regal:

but are actually vicious little beasts with deadly murder claws. : )