[normhead]

That doesn't change anything. My point is that two images taken with the same aperture diameter, at the same distance, with the same subject viewing size will appear to be the same visually.

Of course they'd be the same, everything in that statement is "the same". It would be odd if they weren't the same, now what would be really odd would be if there were a few things that were different and they came out the same.

[audiobomber]

Read it and weep, equivalence doubters!

Equivalence for a lens means same DOF, same FOV, same noise, same diffraction, same perspective. Perspective is dependent on subject distance, so keep it the same for each system. Adjust focal length and f-number by the crop factor. Use ISO to equalize brightness. Here are a few equivalents:

Nikon V1, 1" sensor, 100mm f/2.0, crop factor 2.7X
@ 10 ft. subject distance, DOF is 0.13 ft.
@ 100 ft. subject distance, DOF is 13.4 ft.

Pentax K-50, APS-C sensor, 180mm f/3.6, crop factor 1.5X
@ 10 ft. subject distance, DOF is 0.13 ft.
@ 100 ft. subject distance, DOF is 13.4 ft.

Nikon D800, FF sensor, 270mm f/5.6, crop factor 1X
@ 10 ft. subject distance, DOF is 0.13 ft.
@ 100 ft. subject distance, DOF is 14.1 ft. (The DOF calculator would not allow f5.4, which explains the slight difference in DOF at 100 feet).

Online Depth of Field Calculator

Now let's look at noise equivalence using DXOMark:

Nikon V1, 100mm, 1/300s, f/2.0, ISO 100; SNR is ~35dB
Pentax K-50, 180mm, 1/300s, f/3.6, ISO 350; SNR ~35dB
Nikon D800, 270mm, 1/300s, f5.6, ISO 640; SNR ~35dB

Nikon D800 versus Pentax K-50 versus Nikon 1 V1 - Side by side camera comparison - DxOMark

In summary, photos taken with the above setups will be equivalent in FOV, DOF, perspective, diffraction and noise, i.e. equivalent photos.

[Cannikin]

Of course they'd be the same, everything in that statement is "the same". It would be odd if they weren't the same, now what would be really odd would be if there were a few things that were different and they came out the same.

Focal length and f-number can change, as long as they result in the same aperture diameter. Sensor size can change, as long as you keep the subject's apparent size on viewing constant.

These things can all change and still produce the same DOF as long as they are linked together. Conveniently, this link can be mathematically simplified to a single coefficient, something most now call "crop factor".

---------- Post added 07-16-15 at 06:40 PM ----------

I do my stitching with a shift-lens, accuser-of-brain-damage. Others use rails. So, uh, yes, really.

Your mistake is that, in practice, magnification changes when you stitch.

If you are referring solely to DOF, then theoretically, yes a planar shifted panorama should produce roughly the same visual DOF as the same aperture diameter with a wider angle of view, assuming 0 curvature of field.

Of course the resulting image will look very, very different from a single rectilinear shot with of the same angle of view, unless you intentionally reintroduce, through geometrically calculated simulation, the geometric distortion inherent to rectilinear lenses and reduce parallax to 0. So the comparison between a panorama and a larger sensor is pretty meaningless IMO.

The only completely accurate "panoramic" way to simulate a shot taken from a larger sensor under the same conditions is to shift the sensor only, keeping the lens position and orientation fixed. Anything else will introduce geometric and perspective distortions that do not accurately represent a single rectilinear shot of the same angle.

[jsherman999]

... So don't worry about DoF and sensor size, just get the lens that will give you the output you want on the camera that you have.

But if you want to buy something new, especially if you're trying to improve your output in some way - you do yourself a favor by knowing and applying equivalence. You'll be able to map out what glass you'd need to buy to improve X, for example, and see if it would be cost-effective to you. If you only shoot one format and don't plan to buy another, you don't really need to bother with it.

[Class A]

The DPReview article "What is equivalence and why should I care?" nicely explains how DOF is affected by different sensor sizes.

More in-depth articles are falconeye's "Camera Equivalence" or "The true reasons for a full frame camera" but many people cannot follow the math and hence are better served with the above referenced DPReview article that comes with pictures that present real world examples of how sensor size may or may not affect DOF (and other image parameters).

[Kerrowdown]

Dear Pentax, just give me my FF camera body and I'll deal with all these sort of issues from there, I promise...

[Rondec]

But if you want to buy something new, especially if you're trying to improve your output in some way - you do yourself a favor by knowing and applying equivalence. You'll be able to map out what glass you'd need to buy to improve X, for example, and see if it would be cost-effective to you. If you only shoot one format and don't plan to buy another, you don't really need to bother with it.

I guess.

I think, Jay, that it is a very small number of people who understand photography well enough to know what works and doesn't work in their photos and what gear they really need to make things better. Equivalence will tell you if there are faster lenses available in a given system than what you currently own, but does that truly tell you whether it will improve your output?

I find that folks end up getting confused, changing focal lengths, without changing apertures, thinking that lenses designed for APS-C are different focal lengths than lenses designed for full frame, etc.

It really is a better thing to shoot with the gear you have, enjoy it and if you find that it isn't working for you, figure out what would make it work better. It maybe that a lens or two in the system you are shooting will fix things, it may be that going full frame is a better option. But certainly you need to have some pretty good knowledge base before you try to launch into an analysis of equivalence.

[monochrome]

Originally posted by Mattox "Depth of field?...can we close this argument once and for all?"

Yes, right after we resolve that "chicken or the egg" conundrum.

Is it possible to reproduce the first egg given the tools at hand or shall the second egg be merely equivalent?

[jsherman999]

I think, Jay, that it is a very small number of people who understand photography well enough to know what works and doesn't work in their photos and what gear they really need to make things better.

I think it's presumptuous to think the type of people you describe don't frequent this forum.

Most forum members know more than enough about photography to understand and benefit from applying equivalence to a potential purchase.

.

Equivalence will tell you if there are faster lenses available in a given system than what you currently own, but does that truly tell you whether it will improve your output?

It absolutely does. It precisely addresses the questions most people have when they consider changing or adding a format. Questions like, "if I move from micro-four thirds to brand-X FF, and I want t shoot f.2,8 zooms on FF when I used to shoot f/1.7 primes on m43, would I likely see any noise improvement, would I have the same or better DOF control, and what about DR?"

Or:

"If I'm shooting f/2.8 zooms on FF now, how much of a noise/DR/DOF hit would I take if I shot f/2.8 zooms on aps-c instead? How about if I shot f/1.8primes on aps-c?"

Or:

"I want to move to FF "X" but I need to maintain the same DOF I had with m43 for some stage shots - will I gain any noise benefit? How about DR benefit?"

Or:

"Is there any lens available for this 1'' sensor camera that can approach the portrait 'look' of the FA 50 1.4 o aps-c? If not, what's the closest 'look' I can get? What equivalent aperture could I shoot my 50 1.4 at on aps-c to simulate how lens X would look on 1'' ?"



There are many variations of those ^ types of questions that people ask themselves, and knowing simple equivalence conversions would allow them to set expectations and manage purchases wisely.

(Plus, IMO it's just generally better to not go through life ignorant! )

.

It really is a better thing to shoot with the gear you have, enjoy it and if you find that it isn't working for you, figure out what would make it work better.

That's exactly the point. Equivalence helps you figure that out. It sounds like the alternative you're proposing is to just blindly buy things until you get something you like... Or just keep shooting with something you've reached a limitation with that you're not happy about - without allowing yourself any method to wonder about alternatives, because you've banished equivalence from your list of allowable thoughts.

Anyway as Class A pointed out, see this link if you (anyone) wants a good intro to why you should care.

.

[kh1234567890]

This thread is somewhat lacking in real image examples of 'equivalence' ...



Probably because there aren't any ...

[jsherman999]

This thread is somewhat lacking in real image examples of 'equivalence' ...

Tony Northrup had a pretty nice video in which he demonstrated the differences between formats pretty clearly with actual images, although he kept using the term "Bokeh" when he meant DOF, which is a pet peeve of mine.

The cool thing is that you yourself can create a simulation of format difference with DOF on your aps-c camera - shoot a subject at say 35mm f/2.8, then at 35mm f/1.8. That second shot would give you the look of a 50mm f/2.8 shot on FF - basically the same exposure and FOV on FF, which would result in about 1.3 stops less DOF - and about a stop less noise that the f/2.8 would give you on FF, because that larger sensor gathers more total light for the same exposure. (if you're shooting in low-light where shot noise might be a visible issue.)

Here's an actual shot comparison I did that demonstrates the DOF difference for the same FOV and f-stop - first shot is 50mm f/2.8 on FF, second is 35mm f/2.8 on aps-c:







But you shouldn't need to 'see' examples to know what 1.3 stops of DOF or one stop of better noise performance would give you. Just experiment with the camera/lenses you have. Use that in addition to current sensor-performace data from some place like DxOMARK and you have most of what you need to know about what another lens/body combo would give you IQ-wise.

Think of it this way: If Pentax offered a 50mm f/2.8 lens and a 50mm f/1.8 lens on aps-c, would you demand to see the difference before you'd consider buying the 50 1.8? Would you doubt that a difference existed,for any reason?

.

[Rondec]

I find it really hard to differentiate. I shoot mostly landscapes and I do use film with my Pentax lenses and it isn't like there is a huge difference between the two. I'm sure if I had a digital full frame, I would see some bump in the processability of my images, but just having a slight bigger piece of film collecting photons as compared to my APS-C sensor doesn't seem to make that much difference.

DA 40 on film.



DA 40 on a K-01 camera



DA 40 on flim.



DA *55 on a K-3



FA 31 limited on film.



DA *16-50 on a K-01.

[kh1234567890]

Here's an actual shot comparison I did that demonstrates the DOF difference for the same FOV and f-stop - first shot is 50mm f/2.8 on FF, second is 35mm f/2.8 on aps-c:

I must be a bit slow in my old age - I thought that 'equivalence' meant that you could get exactly the same shot on different sensor/film formats. Including perspective. Obviously I was wrong.

[jsherman999]

I must be a bit slow in my old age - I thought that 'equivalence' meant that you could get exactly the same shot on different sensor/film formats. Including perspective. Obviously I was wrong.

You can get the same image** on two formats, as described by equivalence - but equivalence doesn't say you have to get the same image.

Equivalence simply describes how two formats compare to each other. One consequence of the laying out of these relationships is the realization that you can get the 'same' image on any two formats of the same generation if you are simply willing (or able) to adjust the physical aperture enough. For example, my FF shot above could have been taken at f/4.5 instead of f/2.8 and you'd see the same DOF (and shot noise) in both shots. Or, I could have opened up the aps-c shot to f/1.8. (actually I couldn't have, that was my DA 35ltd wide-open at f/2.8, but you get the picture.)

The OP (this thread) asked about DOF differences and how formats could affect that. My example showed how images on two different sensor sizes shot at the same f-stop and FOV would have different DOF. FOV is the same, exposure is the same... but the image would be different, as predicted/described by equivalence.

** One can never get 'exactly the same' images whenever you swap out lenses and sensors, and equivalence doesn't say that you can. Every sensor of the same size doesn't perform quite the same, and lenses have their own characteristics like sharpness, color transmission and bokeh quality.

.

[kh1234567890]

You can get the same image** on two formats, as described by equivalence - but equivalence doesn't say you have to get the same image.

** One can never get 'exactly the same' images whenever you swap out lenses and sensors, and equivalence doesn't say that you can. Every sensor of the same size doesn't perform quite the same, and lenses have their own characteristics like sharpness, color transmission and bokeh quality.

So, 'equivalence' is a pretty pointless concept in practice.