[normhead]

Shutter speed, exposure and distance from the subject (perspective) must be the same

What about the field of view?

Focal length and aperture must be adjusted for crop factor

So different focal length, therefore different rendering characteristics.

FOV, DOF, DR, perspective, diffraction and noise will all be similar. For me, this is where the meat is, and it is explained by equivalence theory, not by the exposure triangle.

Noise below the threshold of perception doesn't even matter. Including it in your calculation is ridiculous. SO including that in your calculation is misleading. That is the point. For practical photography, no one cares about noise until it's visible. Once again, as you've stated it, equivalence must be tempered by common sense. Who cares if a small sensor camera has more noise than a large sensor camera, if you can't see either?

Or you can just shoot with the camera and see what you get. No need for a theory to figure that out. As far as I'm concerned you can use theoretical constructions like equivalence or you can use empirical knowledge as in developing "common camera sense." Because of the difference in rendering between different focal lengths. The problem of equivalence is it ignores the strengths of the systems used. As I said, 50mm on FF is not the same as 35mm on APS-c regardless of what equivalence said. Those who stubbornly refuse to acknowledge that are missing a lot of rendering wisdom.

Even different 50mm lenses render differently, Planar designs vs. Distagon Designs, heavily corrected vs. less uncorrected, Macro flat plane vs. 77 style (built for the way people take pictures not for the test charts." There is so much more to lenses than straight up focal length. Especially I'm the wide end. The problem I see with equivalence is when people try to use it to ignore everything but focal length when discussing "the same" image. It just isn't everything you need in many situations.

I have actually seen images taken using equivalence where one image or the other is very different than the other. I have no idea why people advocate looking at image creation from such a limited perspective. My 50 macro is not the same as my 50 1.8, yet we have folks creating the notion that you can use random lenses to create the same picture with different lenses on different formats.

Personally, I'm going with "take a few images at different apertures etc, see what you get." Then you actually know how the lens renders, what the DoF is like, how the out of focus areas are rendered. You know what you've got. Not some theoretical nonsense about how they are the same.

I'm wondering, how does equivalence help with the fact that if I take an APS-c image with my 60-250 and the same image with my DA*200 and a Sigma 18-250, which I have done, one image will be better than the others, and there will be noticeable differences. Same format, same focal length. You get different looking images Equivalence can't even predict how you would the same image with different lenses of the focal length on the same format, so how much use can it be comparing different lenses on different formats.

My issue is equivalence it doesn't go far enough. It's too narrow an approach to the image lens selection, ignoring rendering, lens design, and treatment of out of focus areas, sharpness etc. It's a focus on the relatively un-important and ignoring 3/4s of what you should be looking at. Therefore as much a danger to newbies as not understanding equivalence at all.

Equivalence simply doesn't do what it claims to do, because it leaves out so many parameters. It isn't complicated enough to be of much use. And the only lens I bought because of equivalence, the DA 35 2.4, I don't like, at all. It's probably my least favourite lens. Using equivalence instead of actually trying out the lenses will cost you money. And if you can't figure out what lenses you should be trying out without referring to more than the desired focal length and aperture, equivalence really isn't much help.

Or to say it in a sentence, "it's too simplistic."
it gives you a nice ball park figure for math you can do in your head, while ignoring many important elements of lens design. It's half a theory.

I have no idea why this should have to be repeated over and over. What is it here you don't get?

The difference in rendering between different lens designs? The concept of visible noise? What?
With every lens purchase I've made, the part of lens purchases covered by equivalence are the least important, easiest to understand "off the top of your head." Fo the lenses I've had that have moved on, equivalence didn't save me from buying one lens I didn't like, belief in equivalence may have caused or contributed to those purchases.

---

Last edited by normhead; 11-11-2017 at 09:58 AM.

[audiobomber]

What about the field of view?

Focal length and aperture must be adjusted for crop factor

Adjusted focal length already accounts for FOV.

So different focal length, therefore different rendering characteristics.

No, the images will be very similar, assuming corrections are made for crop factor.

Or you can just shoot with the camera and see what you get. No need for a theory to figure that out. As far as I'm concerned you can use theoretical constructions like equivalence or you can use empirical knowledge as in developing "common camera sense." Because of the difference in rendering between different focal lengths. The problem of equivalence is it ignores the strengths of the systems used. As I said, 50mm on FF is not the same as 35mm on APS-c regardless of what equivalence said. Those who stubbornly refuse to acknowledge that are missing a lot of rendering wisdom.

I disagree, per my last post. You have FF and APS-C bodies, with 35mm and 50mm primes. Why not post a comparison shot, so we can see some evidence? K-1 with 50mm f1.7 and K-3 with 35mm f2.4, on tripod, TAv mode, same shutter speed, 1-1/3 stop difference in aperture. I would do it but I don't have a FF body and do not intend to ever buy one. Or even use the K-1 in crop mode for APS-C, though that will further disadvantage the APS-C resolution (only matters for pixel peeping, still plenty of pixels for a large print.)

[Kunzite]

Equivalence explains a lot of things that confuse newbies

That's so wrong I don't even know where to start ranting about it!
Let's just say, I never encountered a situation in which "equivalence" really helped a newbie, but I've seen countless in which it confused them. Remember the classic "let's apply crop factors to FF lenses but not APS-C ones"?

there are still plenty of experienced photographers who do not understand or are unwilling to understand what it is, and what is not.

And many of them are "equivalence" supporters.

I don't think there's much doubt that the D FA 100mm macro would have been smaller, less expensive and just as capable if it had been designed for APS-C. Long telephotos don't seem to vary much, the recent 300mm f4 lenses for Nikon FX and m4/3 are pretty similar in same size nd weight. The new 11-18mm f2.8 would be much larger and more expensive if it were designed for FF. The D FA 50mm f.1.4 would be smaller and cost less if it was a DA* lens. The reason that Pentax has the most complete stable of APS-C lenses is because we did not have a FF body. Fuji is rapidly catching up with its lens environment for the same reason, whereas Pentax now needs to pump out FF lenses.

Are you sure about the 100mm? That's already in the short tele territory, and it doesn't need a retrofocus design. Here "smaller format necessarily means a smaller and cheaper lens" doesn't hold true... as Panasonic just announced their 1.3kg and $3000 200mm monster.
Besides, you're not arguing with my point, which is that we should evaluate lenses based on their characteristics, not on preconceptions.
And cut it out with Fuji praising, please. Whatever they're doing with their X system, adding FF is not an option for them - they would have to start from scratch with a new mount.

[audiobomber]

That's so wrong I don't even know where to start ranting about it!
Let's just say, I never encountered a situation in which "equivalence" really helped a newbie, but I've seen countless in which it confused them. Remember the classic "let's apply crop factors to FF lenses but not APS-C ones"?

Spend a day on DPR's Sony NEX forum. Should I buy an RX100 or a6000 with kit lens? A6500 with18-105mm or A7 28-105mm? These are evergreen questions, and the advice, along with size and cost, always involves equivalence.

And many of them are "equivalence" supporters.

I was thinking of you when I said "refuse to understand".

Are you sure about the 100mm? That's already in the short tele territory, and it doesn't need a retrofocus design. Here "smaller format necessarily means a smaller and cheaper lens" doesn't hold true... as Panasonic just announced their 1.3kg and $3000 200mm monster.
Besides, you're not arguing with my point, which is that we should evaluate lenses based on their characteristics, not on preconceptions.
And cut it out with Fuji praising, please. Whatever they're doing with their X system, adding FF is not an option for them - they would have to start from scratch with a new mount.

I couldn't find a 100mm f2.8 macro in m4/3 or APS-C, but my reasoning is that you could use smaller diameter elements and a narrower barrel for an APS-C version.

I do evaluate lenses based on their characteristics, but one also must consider the camera the lens is mounted on. Lens and camera together determine FOV, DOF, sharpness, etc, not just the lens itself.

I'm no Fuji fan, the X-trans sensor has become a near fraudulent marketing gimmick, IMO, but they are are offering a lot of APS-C lenses and growing.

[Kunzite]

Dan, I understand "equivalence" much better than its proponents - as proof, I'm able to realize how useless and dangerous it is. They're not.
And if it's about refusing, you are refusing to acknowledge the damage it does. I gave you a recent example from this very forum, I don't even have to go look elsewhere.

What you don't get it, is that you must consider only the camera the lens is mounted on. We're not talking about inter-format comparisons, but figuring out if e.g. a lens is wide or not - on one specific format.
To an APS-C user, saying: "this lens is as wide as a 35mm on FF" is useless - they don't know what a 35mm on FF looks like. Forcing them to relate to something which is unknown to them - as opposed to that which they can experience directly - is not helping, but confusing them.
But I've made this argument before. What did you say about refusing?

[audiobomber]

Dan, I understand "equivalence" much better than its proponents - as proof, I'm able to realize how useless and dangerous it is. They're not.
And if it's about refusing, you are refusing to acknowledge the damage it does. I gave you a recent example from this very forum, I don't even have to go look elsewhere.

What you don't get it, is that you must consider only the camera the lens is mounted on. We're not talking about inter-format comparisons, but figuring out if e.g. a lens is wide or not - on one specific format.
To an APS-C user, saying: "this lens is as wide as a 35mm on FF" is useless - they don't know what a 35mm on FF looks like. Forcing them to relate to something which is unknown to them - as opposed to that which they can experience directly - is not helping, but confusing them.
But I've made this argument before. What did you say about refusing?

What you are advocating is ignorance. Equivalence explains a great deal about "sensor plus lens" interaction and allows cross-systems comparisons. Personally, I find it highly useful.. Others do not, which is fine with me. Denying that equivalence has merit I do not understand, as it explains much about current digital photography and the performance envelope of various formats available to photographers.

[Kunzite]

I'm advocating... ignorance? Do you have to insult me, Dan? Is this "equivalence" of yours so important, that you'd change the tune of this discussion to a completely unfriendly one?

Don't ever confuse "equivalence" with knowledge, Dan, even though they rhyme. "Equivalence" is not knowledge as it didn't introduce anything new - except a rigid yet frail methodology of comparing different formats, and a set of assumptions that can't be met IRL.
But perhaps even the Masters of photography were ignorant, as I don't remember them ever needing this "equivalence". The fools, they were talking about focal length without applying crop factors, apertures which were used for exposure - too bad you weren't there, to show them!

---

Last edited by Kunzite; 11-11-2017 at 01:39 PM.

[HarisF1]

Some of you guys get so offended so quickly. Just like in the 11-18 thread, you're being pathetic again.

Live and let live.

[Kunzite]

you're being pathetic

And some guys are throwing insults so quickly. "Let live"?

[audiobomber]

I'm advocating... ignorance? Do you have to insult me, Dan? Is this "equivalence" of yours so important, that you'd change the tune of this discussion to a completely unfriendly one?

Don't ever confuse "equivalence" with knowledge, Dan, even though they rhyme. "Equivalence" is not knowledge as it didn't introduce anything new - except a rigid yet frail methodology of comparing different formats, and a set of assumptions that can't be met IRL.
But perhaps even the Masters of photography were ignorant, as I don't remember them ever needing this "equivalence". The fools, they were talking about focal length without applying crop factors, apertures which were used for exposure - too bad you weren't there, to show them!

There was no insult offered. Maybe a language barrier? Ignorance: lack of knowledge or information

In the context of what I said, you are advocating to withhold knowledge of equivalence from novices. I say teach them what it means, which is education, the opposite of ignorance. It's hard to teach though, against so much resistance.

Old timers didn't discuss equivalence, that doesn't mean it didn't exist or was not applicable to large format, 35mm and 110. Obviously it is a frequent topic of discussion now, and the subject of many blogs and technical articles. Denying it will not make it go away, because it is a useful concept and quite enlightening when used properly. I hope Norm agrees to provide an equivalence comparison, then we will have something more concrete to discuss. I predict that the differences in IQ will be trivial compared to the blatant and obvious similarities.

[Kunzite]

No, Dan, what I'm advocating here is to stop confusing novices with this "equivalence" nonsense. I explained why and how, at this point you're just refusing my arguments.
Teaching them nonsense is not knowledge; you're doing a disservice to the photographic community by insisting so much on it. They're having doubts regarding the most basic notions like focal length and aperture opening; they're applying crop factors when they shouldn't, they're applying crop factors to some lenses but not others.

And you still don't want to accept that we're talking about a case which didn't involve any cross-system comparison. This is the most important part of this discussion.

[BigMackCam]

Ok, fellas - breathe Relevant discussion, but please let's keep it friendly and not personal. Thank you

[BigMackCam]

At the risk of extending an equivalence discussion I've already intervened in (!), and one that is verging off-topic from the original post, I feel I have to say my piece

I agree that, generally, it's a waste of time to worry about equivalence... Shoot with the lenses that give you the results you want on the sensor format you have available. That's all that really matters.

That said...

Some owners of APS-C format cameras want to be able to reproduce what they see from full-frame photographers. That's quite understandable. I've been in that situation, and so have plenty of others here.

The main issue, as I see it, is one of subject isolation using limited depth-of-field.

If someone shoots an image on a full-frame camera with an 85mm f/1.4 lens at - say - f/2, it will have a particular field of view and depth-of-field relative to the subject. To recreate that same image with an APS-C camera, I would need to shoot at the same distance with a 56mm lens at f/1.3. No such lens exists, so - clearly - I couldn't recreate that shot *exactly*. I could, perhaps, use a 50mm f/1.4 lens wide open to get a similar field of view and depth-of-field, but (at best) it would be an approximation (and suffer from the imperfections of a lens used at maximum aperture).

The situation becomes even more difficult if we consider an image from that same full-frame camera plus 85mm lens shot wide open at f/1.4. To reproduce that with my APS-C camera, I'd have to use a 56mm lens at f/0.93. Again, no such lens exists. Indeed, there isn't even a 50mm lens I know of that has such a large maximum aperture - so, in this case, I simply couldn't take the *same* shot with my APS-C camera. This is one area where the APS-C format is potentially limited compared to full-frame (if you look at it that way)... shallow depth-of-field for a given field-of-view is limited by the maximum aperture of available lenses at the necessary focal lengths.

Of course, there are plenty of benefits to using APS-C too. For example: If greater depth-of-field is my priority, I'm laughing. If a full-frame photograph is taken using a 300mm lens at f/5.6, I can take an almost-equivalent shot from the same distance, using my APS-C camera and a 200mm lens at f/3.5 to f/4. I'll get very similar depth-of-field and, as a bonus, for the same shutter speed I can use a lower ISO.

But I return to my opening agreement with some of what has already been said... it's a waste of time to worry (too much, at least) about lens equivalence between sensor formats... Shoot with lenses that give you the results you want on the sensor format you have available. That really is all that matters

[Digitalis]

I agree that, generally, it's a waste of time to worry about equivalence... Shoot with the lenses that give you the results you want on the sensor format you have available. That's all that really matters.

This is what I teach to my colleagues and students, even those who espouse the virtues of equivalence. Eventually my words will sink into their skulls.

Some owners of APS-C format cameras want to be able to reproduce what they see from full-frame photographers. That's quite understandable.

Understandable, but deeply flawed.

At the most fundamental level lenses are filters, limited by their own aberrations at wide apertures and diffraction at small apertures - there is a point where a lens will perform its best. In the end you have a lot of choices when it comes to IQ: If you are shooting on a smaller format than for which the lens was designed for, are you going use equivalence in an effort to mimic the DOF of the larger format, even though it will likely result in inferior image quality? or are you going to stop the lens down and go for optimum image quality?

Personally I advise to stop the lens down, this is why I think the Pentax MTF program line is a stroke of genius.

[BigMackCam]

Understandable, but deeply flawed.

At the most fundamental level lenses are filters, limited by their own aberrations at wide apertures and diffraction at small apertures - there is a point where a lens will perform its best. In the end you have a lot of choices when it comes to IQ: If you are shooting on a smaller format than for which the lens was designed for, are you going use equivalence in an effort to mimic the DOF of the larger format, even though it will likely result in inferior image quality? or are you going to stop the lens down and go for optimum image quality?

Agreed. No argument with that from me. I think, though, that most amateurs concerned about equivalence (and I include myself, back when it bothered me) aren't considering, or even aware of, the details of a lens' optical performance in this situation... they just want a broadly equivalent field of view and depth-of-field on the format they're using. They most likely don't even fully understand what they want - and that's no criticism of them, but simply an observation based on my own journey