What Is Equivalence?

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Good example ... not exactly equivalent (by image size) but certainly good enough for the purpose of demonstration.

This is where you have either misunderstood the meaning / purpose of equivalence or intentionally ignore it.

Equivalence doesn't "define the difference between cameras". It defines how to take images that are equivalent (within the 6 parameters - no more, no less) from cameras with different formats.

Subjectivity is NOT one of the 6 parameters. Subjectivity does NOT enter into the equation.

Fortunately science learnt quite early that subjectivity should be ignored. Science relies on repeatable observations...

Can you imagine, in the early 20th century (1900's) when the physicists were learning about atomic structure, observing cloud chamber images, that they argued about subjective interpretation of those images? Physicist A: "I think that curve has radius 1.0" Physicist B: "No, it looks more like radius 1.2. Therefore we can't say what it is." Physicist C: "Well my ruler says 1.0. Are you implying my ruler is wrong?"

Postgrad students design a new cloud chamber with higher resolution - the images are twice the size. Physicist B: "The curves now look like they have a different radius - we can't use them". Physicist A: "Lets define cloud chamber equivalence - if we scale one of the images so they have the same size we can compare the curves - we can still measure them if we define the axes correctly". Physicist C: "That works for me..."

Elsewhere - Einstein: "E = MC^2". Physicist B: "Well I think it looks more like E = MC^2 / 1.1". Everyone else: "groaaannnnnn"

And as I said a long time ago, I don't see the point of equivalence if all it does is instruct on how to use the camera as a copy machine. And it only works with the same photo, the only examples ever posted are the same photo... (Though I think me and GB thrashed it out as to the relevance and limits of equivalence already).

If you want to quote the ridiculous to make a concept sound ludicrous...

I'm quite sure that physicists fully appreciate the nature of the instruments they use to measure things and thus generally don't build atomic bombs by weighing things by eye either. In fact I'm sure that they are fully aware of perceptual problems and probably use a ruler.

the exif data is not showing 🤨

So we want a subjective conversation about some images of the same scene taken with two different formats.

Can you understand that it helps if certain parameters of the image making process are held constant? So as to stop the conversation drifting into certain physical aspects and thus allow the conversation to be purely subjective?

I don't think you can have it both ways - unless you want equivalence parameters in the conversation as well - which is the choice of those having the conversation.

However for those that want a conversation where those parameters are held equal, that is their choice as well - which CAN allow a purely subjective conversation.

I think you would agree that life isn't science. Trying to use science to describe life at the very least shoehorns it into something it isn't. However science is very good at defining certain aspects of life and allowing us to concentrate on other aspects.

I don't know if you have been exposed to multi variable calculus. There is no one solution to those equations. However there are sets of solutions and solutions definable by setting certain boundary conditions. Without those methods there would have been no moon landing. No returning to earth and entering the atmosphere at just the right angle / speed. No outer solar system missions using a planet's gravity to slingshot onto the next planet. And many, many more solutions that give us some of the tools / utilities we find in society today.

And in regard to equivalence in cameras the ruler is?

Sorry, but I really don't understand the post. I don't see why we need to copy a photo with a different format to enable a subjective conversation about it's creative merit. Surely you mean if we level the creative/subjective then we can have an absolute discussion about the relationship between the formats.

Yes, life isn't science, and there are aspects of science and calculus that have allowed us to do amazing things. But I don't see what that proves except that you can have it both ways.

And isn't equivalence the ruler in photography? And isn't the maxim of creativity "rules are made to be broken"?

I'll just be repeating myself so I'm away now.

I took the trouble to download each image separately and got the sizes and framing from them.

The sizes and the framing should be equal for 100% camera equivalence. Yours are not equal but they are indeed close enough.

There is something intrinsically weird in that we need to be able to see and examine the numbers in order to define a photo correctly. In a nutshell what I see as the problem with equivalence, our definitions follows a nomenclature based on our understanding of how cameras work rather than how photos work.

i understand that, but there must be a problem with the site , as it shows the exif when i first post the images then it disapears when you close the site then re-open.

Sorry to hear that, maybe Alan can fix that.

Meanwhile, the exif shows every time I open your posts on this particular topic:

Creativity is orthogonal to Equivalence. The advantage of a larger format over a smaller format comes from taking photos that are not Equivalent. If all you ever did was take photos equivalent to a smaller format, then you're almost certainly going to be better off with the smaller format, unless the larger format has a lens or operational advantage not available in the smaller format, or you just prefer using a larger and heavier system.

Nothing of the sort. Equivalence merely relates the camera settings on different formats to a set of particular (but important, and, I would argue, central) visual properties. However, understanding the principles of Equivalence is good to know, in my opinion, because then you have a better understanding of the technical elements of photography, such as why "zoom with your feet" is a misnomer and why aperture, exposure time, DOF, and noise are all related. I think these kinds of things are good to know. And, no, you don't need to know Equivalence to understand these things, but Equivalence puts it all together in a nice, simple, and concise framework.

I think it's important to differential between rules and guidelines. Equivalence gives rules. For example, if you move, you necessarily change the perspective. If you want a less noisy photo, then you necessarily have to use a longer exposure time (which includes stacking multiple exposures, since the aggregate time is longer) and/or more shallow DOF (due to the wider aperture).

On the other hand, "rules" like "Rule of Thirds", are not rules, but guidelines. So rather than saying the maxim of creativity is breaking the rules ('cause rules can't be broken), I think it's better to say that the maxim of creativity is exploring possibilities within the rules. Still, I'm a huge fan of, "Just because you can, doesn't mean you should." However, if it can be done, it will be done. It's simply a matter of time and you knowing about it.

Pretty sure Don's photos were simply meant to be an example of photos taken from the same position with the same angle of view and aperture diameter, display at the same size with the same viewing conditions, results in the same DOF. No more, no less. Trivial? Sure. More controversial would have been if he had done the same with the same exposure time in very low light so that he would be using significantly higher ISO settings to demonstrate noise equivalence. Anyway...

Is that true in relation to your first statement, and is that first statement true?

Creativity is orthogonal to Equivalence.

There is an excellent book, "Photography a Concise History - Ian Jeffery". First published in 1981, so only deals with film, but a fascinating look because it explores the visual impact of photography, not the technical history. The trouble with equivalence is that it's myopic in the sense that you're only looking at digital cameras that are currently owned or available to buy. And then we are only looking at the measured effects of the physical controls (focal length/focus point/aperture/shutter/ISO) of cameras that are broadly similar in performance. Besides your language in the paragraph is very definitely about creating a logical order based on the capabilities and so suited tasks of your broadly similar cameras, (the difference in your selection criteria, not the history of photography), and not about using the wrong tool for the job, which is a very widely known and used creative process.

Besides, what about the change from film to digital, digital editing possibilities, instant visual access and it's effect on learning, the rise of the camera phone and social media, the effects of self publishing and the removal of centralised editorial control. Also we have learnt to decipher and add meaning to photographs based on a whole lot broader spectrum than the physical camera controls used to define equivalence. Like language itself the visual language of photography is the meaning we choose to define words and phrases by, ones that have relevance to us, now, with our experience and memory, our irrational impulses and emotions. Pulling things back to a fixed framework of rigid definition backed up by maths proven by example is almost the very antithesis of this.

Given that the only examples that are shown in this very thread (so far) are the exact same photo, I would say that all we've proved so far is that Equivalence is orthogonal to facsimile.

Now, I've added italics to the second half of this quote because I broadly agree, with it all. But not the first part. This is the problem of looking only at the camera and the resultant image whist ignoring perception. You form an absolute "cause and effect" understanding between the controls available to you and their "measured" effect on the absolute nature of the resultant image. Then, as above, substitute "measured" with "visual" with nothing more than assumption based on a desire for there to be a technical answer that has the beautiful symmetry that Equivalence offers, (there I'm even spelling it with a capital letter now, I've been exposed too long... 😁). I say you're missing a vital and creative understanding because by trying to tie the controls of the camera to the absolute you miss the understanding that images are far from absolute and are quite elastic.

I'm going to try a little demo, that may work, may not, you may not play, some may be resistant to different ideas and so unwilling to see. Keep in mind the mathematical construct of equivalence, (I'm cured!!) Below are three photos and the game is, which have equivalent or similar AOVs. I'm testing whether AOV (one of the constants of equivalence) actually transfers as a visual property of an image and can be used as a creative tool, or whether because you fail to include perception in equivalence you miss the actual visual effect of AOV.

I'm sure that if people do play they will also be zooming in and looking for the absolute in the images that allows them to associate the images with actual numbers. Which is OK because that too is human, but I ask that you also look honestly, as a casual observer of images as the general public would. Specifically, does the visual style of the photo give away clues about the actual AOV (rather than it being a visual property of the image). And if the maths of equivalence (and perspective) were broadly true but elastic then what would be the visual effect of mistaking say a wide angle shot for a telephoto one? Would it be broadly the same as squashing the mathematical model in that if we squish a broad cone into a narrow one whilst maintaining the volume does the image also appear to to stretch in distance?

As I said before, are you sure equivalence really helps, or is it presenting us with such a seductively symmetrical solution that we fall into the trap of substituting "measured" with "visual"? Sure, it can save you money and a sore back if your bag is birding, but is it really a creative tool? I find it restrictive.

The problem is, (and I know it's not the point of equivalence, but it's the result), that this conversation and others like it stretch out and invariably end up with comparing identical photos and a discussion on whether the photos conform to the exact mathematical definition of equivalent. I don't see it expand to a creative application of the knowledge. Sorry, but as an outside observer a measure of a theory is also an examination of the actual results it produces...

Forgot, I'm away for a while now and don't log in from my phone, whilst away. So all 5x4 full negative so focal lengths in order posted 150mm/90mm/240mm. The relationship between the stumps and the wind farm is not as honest as it appears.

Equivalence is just a way to talk about the equalization of potentially visible parameters (besides equal angle of view) of an underlying analog image based on the pupil size and the focus/subject distance, translated into the parlance of exposure, ISO, focal length, and f-number, for those immersed in that film-exposure paradigm that has survived into the digital age. It is not supposed to have anything directly to do with creative aspects of photography. Obviously, if you have a very small sensor, then nothing equivalent to a FF with a very fast f/1.4 lens exists, and one could be potentially forced to accept more DOF than they really want which may affect the creative process, but there is a large range of deeper DOFs where you don't need a larger sensor to get the same underlying analog image for a given AOV, and the theory of equivalence points that out to people who are not pupil-oriented in their thinking.