[goodnight]

Most of the people who have been here a while get it with some exceptions. Then we get someone who posts something and it turns into a 15 page thread...

I just don't participate in those threads for the most part.

It seems to be triggered by mentioning light and sensor size.

Uh oh.

You hear that rumble in the distance? The equivalists are coming! Head for the hills!

[Na Horuk]

I was expecting this thread to go bad real fast, but the replies so far are pretty great. 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.

[normhead]

I think it's quite simple: 50mm f2 at 3 meters (or whatever f-stop and distance) will give the same dof on ff-, aps-c-, mft- or whatever-sensors. but because you want to get a specific angle (not focal length), you will take a few steps back when using a smaller sensor - and that changes your dof (further away=more dof). or you change to a shorter focal length lens and stay in the same place (as shorter lenses always have wider DoF), which also changes your DoF.., or any combination of those two things.

I was thinking about these topics the other night.. and I was thinking, we used to have people tooting equivalence, but misusing it to imply it proved FF had a one stop light and noise advantage , which is what most popular sights do. Then you have others who will say equivalence is just wrong. It's not wrong, it's just pretty much irrelevant.

There is a grain of truth in both arguments.

FF does mean you can shoot for really narrow DoF at say ƒ1.4 in low light and there might be a difference between the APS_c and the FF shot in such circumstances. There is a teeny tiny little advantage to FF systems, if and only if certain shooting parameters are met. Between ƒ1.8 and ƒ16, where most of us do most of our shooting, APS-c has more DOF than FF at the same ƒ-stop and there is no disadvantage to APS-c, and uses the same amount of light and creates the same amount of noise for the same Depth of field.

When people are saying they don't believe in equivalence, sometimes they're really "saying I don't believe that applying 'equivalence' as theory in any way improves my photography." And that as well is a totally valid point.

But as noted earlier today, there is now starting to be information disseminators on youtube etc who are attacking equivalence as a theory... but the main thing I've noticed is, you can walk people through equivalence and everyone comes to their understanding, which may not be in agreement in each other but since equivalence is pretty much a self obvious phenomenon, no one has to get it completely right. It's pretty much superfluous as a theory. It explains things, but doesn't help your real world photography. (People will say different, but there is absolutely no need to understand equivalence, if you are a careful student of the effects of each lens you use on each format you use it on, you will understand equivalence completely without the math.

There are a lot of people who say things like "I use equivalence all the time." What they don't realize is a lot of us used equivalence all the time before "equivalence" was a thing. You don't have to know the theory of equaivalnce to use the phenomena equivalence describes. What we used to know was, "for a bigger format you need a longer lens to do the same thing." That's all you need... no math, you compensating for noise and aperture and DoF. I can tell you, these clowns championing equivalence all over the place don't know anymore than we did. They've just for some reason wed their psyches to this theory.

You can interpret equivalence to promote any format you choose as better than every other format out there. For any little corner of the equivalence table, you can find an advantage for almost any format, especially when you get into the magnification factor in a system like the Q, where you get very wide DoF for your FoV. Every system has it's sweet spot. When you look at evrything, you can use equivalence to make any system look good or bad. The question in my mind in these kinds of things is not about equivalence. It's more like "Why is the poster doing this, what's his angle?"

Every actual expert I've read that discussed equivalence has said " the point of equivalence is not to prove one system is better than another." People who do that should be taken with a grain of salt. It's completely limited to what lenses to use on what format for the same field of view. Anyone who says equivalence proves the superiority of one system over another, doesn't understand equivalence. It's pretty much format neutral. It's human interpretations that try and ascribe format values to a pretty much format neutral concept.

But we get new salvo's from new people who are excited about some internet blog, and the information can be biased in three different ways. SO if we really want to put equivalence to bed, we're probably going to have to have the forum delete the word from all posts. There seems to be a new wave of interested parties from time to time. And the same things are gone over, over and over again.


Note as to the state of equivalence discussions.

I'm going out on a limb here, and I'm going to suggest that physicists schooled in refraction but not optics are probably the most obtuse posters on the forum. They seem to often barely understand photographicly important subjects like DoF, and Aperture and phrase their posts in such a way, that if you didn't know what they were talking about, before you read their posts, you wouldn't be any smarter after you read their posts. And if you did thoroughly understand before, it would still take an in-ordnate amount of time to check their work because of their manner of expression is somewhat unconventional.

It sort of re-inforces the old thing about the scientist who works in his lab, and does great things, but can't explain anything to laymen.

I'm sure they are smarter than me. I'm just also sure you have to be someone who is smarter than them to completely understand them, and even smarter than that to be able to understand what they are talking about, and put it out there in laymans terms so everyone can understand it.

[Mattox]

There we go. A clean unconfusing topic that got to the point and that will be useful for future reference I thought. And yes the topic has been touch on so many times but I have always read about it through other mixed threads.

[ElJamoquio]

Depth of field?...can we close this argument once and for all

Newbies.

[alamo5000]

There we go. A clean unconfusing topic that got to the point and that will be useful for future reference

We can hope but I doubt most people will search for it. When the questions keep coming up just link to this...if everyone does it then hopefully it will help...

[Pål Jensen]

It's not wrong, it's just pretty much irrelevant..

I said that years ago somewhere on this forum....

[osv]

it's not wrong to say that we indeed get pictures with more depth of field using APS-C cameras given that we're talking about the same aperture setting.

that is wrong, and we've covered the reasons why about a million times already

you don't get "more dof" with any format... not aps-c, not m4/3, not ff, etc.

if you want to compare formats, ignore the printed number on the lens barrel, and compare only light, dof, and fov.

[promacjoe]

The explanations given are not exactly wrong, But they are not exactly right either. The fact is that all lenses want to present their image on a curved surface. Since our sensors are flat, lens designers try hard to correct this problem. Some do a better job than others. The end result is that the outside corners are more out of focus than the center of the image. this out of focus range may be imperceptible in most lenses and very noticeable in others. It also means that depth of field between two manufacturers of lenses may be different. The end result is a lens designed for large-format camera will give a better depth of field on a Camera using a smaller sensor. end result, the depth of field that you get is relative to the lens you're using versus the aperture. And, although it might be imperceptible a lens that uses a different design will probably have a different depth of field.

A good lens design will have a fairly even Field of view across the entire frame within the same flat plane. A poor lens design will not.

Where does that leave us as photographers. We should concentrate on the end results, not the specific lens design. Learn how to use the lens that you have to get the most out of it. And if you find a lens that does a better job for your style of photography, get it.and learn how to get the most out of it.

[osv]

The explanations given are not exactly wrong, But they are not exactly right either. The fact is that all lenses want to present their image on a curved surface. Since our sensors are flat, lens designers try hard to correct this problem. Some do a better job than others. The end result is that the outside corners are more out of focus than the center of the image.

that's true, and if you are going to talk about field curvature like that, you might as well bring up issues like decentering, which can sometimes be hidden by stopping the lens down.

if you don't understand... poor design and defects can give blurry frame areas that could be confused as a dof problem.

[fuent104]

The simplest way to understand it, in my opinion:

DOF is dependent on magnification +f-stop + senor size.

For any given sensor size, DOF will be pretty much the same no matter what focal length you use, if the magnification and f-stop are the same. A closeup of a person's face on aps-c will have one eye in focus if you shoot at f1.4, whether you use a 15mm lens or 100mm lens. A full body shot will have the whole body in focus if you shoot at f8, no matter what focal length you use.

The same principles apply for the same sets of variables, but on different sensor sizes, with shooting on the sensor sizes resulting in more or less DOF, at any given magnification factor + f-stop.

[normhead]

I wouldn't endorse any description of DoF, that doesn't describe circles of confusion, and the concept of acceptable focus, as different from sharp focus, the effect of contrast and micro contrast on the appearance of sharpness and probably a few other variables I don't even know about. I'll know what they are when I read about them and say "Hey, I didn't know that." I want a couple of those in the explanation.)DoF is way more complex than a a half paragraph explanation. And it can be observed and understood, as opposed to statistically analyzed and understood. Trust me, observation and measurement more than the theory of acceptable focus is the way you want to go. Practical experience of tens characteristics is what makes you a photographer, understand the relationship in photo systems from a theoretical perspective makes you a optical physicist, or possibly a lens designer.

Depth of Field is the distance from the nearest to the furthest point in acceptable focus.

[dms]

Since you view the results at different magnification (either on screen or on print) the DOF does change. You don't print/view at 2/3 the size with the cropped sensor.

[fuent104]

Since you view the results at different magnification (either on screen or on print) the DOF does change. You don't print/view at 2/3 the size with the cropped sensor.

What do you mean when you say you don't print / view at 2/3 the size?

[romay]

It seems to be very widely believed that a smaller sensor means "less light", and so the aperture must be adjusted for a smaller sensor the same way the focal length is.
The easiest way to say it, is that it's just flat out incorrect. It's simple mathematics. I never had much luck explaining it clearly unless it was in person rather than over the internet. However, this guy has made several videos on this exact subject, and he (though a bit long winded) explains it very well.
Video 1:
Angry Photographer: VIDEO 1 Correcting the LAST of the FX vs. DX "more light" nonsense - YouTube

Video 2:
Angry Photographer: VIDEO 2 Correcting the LAST of the FX vs. DX "more light" nonsense - YouTube

I watched those linked videos and I think you should take them with more than a grain of salt.
While the guy is correct in that the light density has nothing to do with sensor size (which should easily be explainable without a video), most of the other stuff he rants about is pretty specific to the argument he had with that other guy. Without knowing that discussion, 95% of the stuff he says just doesn't make any sense at all.

And yes, for a bigger sensor, the total amount of light gathered is higher, which equals more information in the final image. Assuming identical framing and pixel density, the bigger sensor will always be sharper. Assuming equal framing and same pixel count, the larger sensor will always exhibit better S/N ratio.