Crop vs Full frame

Capturing
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A great video by Zack Arias about the real differences between crop and full frame
I found it enlightening

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Fun! He’s always neat to watch. I love his tutorial on shooting white seamless (seems to be half-gone now - but the text is still there and valid).

His points are certainly valid. If folks spent half as much time learning to build their vision and eye as they did arguing about the technical aspects of imaging systems, well, we’d have more pretty photos to look at. :slight_smile:

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I’m not quite sure what to take away from this video. The essential statement seems to be that a factor of two is negligible. Sure just as the difference between f/1.2 and 1.8 is negligible, and between ISO 3200 and 1600. Is APS-C ‘good enough’ for most things? I think so. Is an APS-C + F/1.2 lens that much smaller, cheaper or lighter than a fullframe + F/1.8 lens? Not really. The equivalent lenses might actually make it a heavier and pricier option.

I guess that’s just the grumpy engineer in me talking. But to me the entire point of the discussion is moot. There are differences, and we mostly know what they are and when they are relevant and when not. Pointing at pictures with a stick doesn’t do it for me. :confused:

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I feel like his main point is simply that the technical arguments around gear do little in the way of advancing a persons eye for composing images. The limiting factor for the majority of folks is not what the technical aspects of the camera are, but rather the 12 inches behind it…

That’s what I got anyway.

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I got the same as @patdavid
It’s not about gear, but about the whole process in making a good photo

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This is true (and made me laugh a bit - where do I get a stick to poke things with?) :slight_smile:

Actually, this is a more interesting point on thinking about it. Some of us may know what the differences are and when they’re relevant, but should we consider finding a way to pass this information on to others in a better way?

Any takers to write something? Or record something?

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For one we should stop telling people that applying a crop factor tells them what lenses can be compared. It’s just plain wrong that a 80mm on full frame results in the same image as 50mm on APS-C. The only way to turn a full frame image into one that looks like a cropped image is by cropping it. Everything is plain wrong.

Edit: i switched 50 and 80.

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Great point! Everyone is so used to hearing that as a means to compare field of view, that they don’t think about the other important lens characteristic differences.

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But it does work like that.

135/4 on full frame looks pretty much identical to 85/2.8 on crop.

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[quote=“patdavid, post:6, topic:422”]
Actually, this is a more interesting point on thinking about it. Some of us may know what the differences are and when they’re relevant, but should we consider finding a way to pass this information on to others in a better way?
[/quote]The better article would probably be how does a camera work. And if you could actually find someone familiar with it how do lenses work. The rest should follow from that.

[quote=“CarVac, post:9, topic:422”]
135/4 on full frame looks pretty much identical to 85/2.8 on crop.
[/quote] In theory, if lenses and cameras were perfect. In practice it’s of course a little bit different because there are fixed things like the wavelength of (visible) light and the physical properties of the materials/glass available to construct lenses.

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Hmm?

The wavelength of light being fixed is compensated for by the fixed entrance pupil size due to using the 135mm at f/4 and the 85mm at f/2.8. Obviously different lenses will perform differently, but my 135/2.8 and 85/2.8 behave extremely similarly (nearly-perfect at equivalent apertures) and when I was using the 135 on the 6D I rented it was exactly like the 85 on my 60D.

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Disclaimer: I’m not very familiar with optics I might well be wrong about this.

[quote=“CarVac, post:11, topic:422”]
The wavelength of light being fixed is compensated for by the fixed entrance pupil size due to using the 135mm at f/4 and the 85mm at f/2.8.
[/quote]As far as I know the fixed entrance pupil size will mean that they have the same amount of diffraction, due to that pupil. What will still be the case is that the lens needs to bend the light more (the light will come in at more oblique angles), which I would expect to cause more issues with CA and Vignetting. It’s of course much less of an issue when you work at the focal length’s and apertures you stated. It becomes quite relevant. So I would totally question if a Voigtlander Nokton 17.5mm f/0.95 Lens for four thirds performs similar to a 35/f2 on a full frame.

[quote=“patdavid, post:4, topic:422”]
I feel like his main point is simply that the technical arguments around gear do little in the way of advancing a persons eye for composing images. The limiting factor for the majority of folks is not what the technical aspects of the camera are, but rather the 12 inches behind it…
[/quote]That is certainly true.

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Oh, definitely true. That’s the real advantage of larger formats: it’s easier to make a perfect lens with a given entrance pupil size if you have a longer focal length because the f-number is larger. It’s probably very easy to make a large format lens crazy sharp at f/8.

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And that’s exactly what is not the case. Optics don’t work like that.

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What do you mean that “optics don’t work like that”?

This is from personal experience. They look identical, and they should be. The biggest telltale difference is the aperture being hexagonal in my stopped down 135.

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Well, there are many things that characterize a specific focal length. The field of view is one, but there are also things like distortion or compression of the background. By multiplying with the crop factor you can get an equivalent field of view, however everything else stays the same. A 50mm on crop will have a field of view like a full frame 80mm, but it stays a 50mm, so you still get big noses when shooting portraits, … Granted, the longer the focal length gets the less that matters as the typical distortion of long lenses is not as pronounced as that of wide lenses.

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Big noses in portraits only depends on lens distortion and subject distance. Assuming good lenses, distortion is the same (zero).

Subject distance should depend only on field of view, which is equivalent.

Background compression is also only affected by subject distance and angle of view, thus only by angle of view, which is equal for equivalent lens/sensor combinations.

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I was thinking about this some this morning, and the best way to approach the topic in an approachable way.

What I thought about was this:

  1. The focal length of a lens is a function of the lens only (not the camera).
  2. The aperture of a lens is a function of the lens only.

If I take an 85mm lens on a full frame camera, and then take the same shot, same location, focus, etc., but use a crop camera, I should end up with an identical image in every way, but cropped to a smaller portion of the full-frame image. This should be the case, right? (I don’t have the hardware to test this idea at the moment, but I think it should be true - the resulting image being created from a given lens doesn’t care what type of capturing medium is on the other end).

So, same exact lens, crop vs. full frame camera = same image, just cropped to a smaller portion of the resulting image. The optical characteristics of the 85mm are not changed in any way with crop vs. full frame except for a smaller area of capture.

This thought experiment works in the opposite direction as well. Use a lens designed for a crop camera, and shoot it adapted to a FF body - you should get an identical resulting image for the most part.

Does this make sense?

TL;DR: a 50mm is a 50mm regardless of what’s actually capturing the image it creates. You just might end up with a smaller FoV on a crop.

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The point is not what gets an identical image, but rather an equivalent one when using the full potential of your equipment.

If you wanted the same field of view as 85 on crop, you wouldn’t crop from an 85mm on the full frame camera. You’d use a 135mm, one stop down, because it’s equivalent but better.

135/4 on the whole 36x24 frame is pretty darn close to equivalent to 85/2.8 on Canon’s APS-C sensor. Same angle of view, same depth of field given a given subject distance, same amount of background blur, same amount of diffraction-“limited” resolution.

However, since usually you’re sensor performance limited, on full-frame you’ll generally have more resolution and dynamic range and so on. And so we talk about using equivalent lenses: 25/1.4 on M43 is equivalent to 50/2.8 on full frame.

In my mind, that’s completely wrong. 50mm is just a number if you don’t know the sensor size; field of view is what really matters. 50mm on a Hasselblad is not 50mm on m43. It’s a completely different use case, and unless desperate, nobody would ever use the wideangle 50mm on a Hasselblad for the purposes that a short telephoto 50mm on M43 is suited.

I’m an advocate for completely ignoring the physical focal length except when identifying a lens model.

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My point here was only to demonstrate that using an 85mm lens on a crop sensor does not magically imbue it with any characteristics of a ~130mm lens. It only produces the same field of view you may get. The rendering characteristics of the lens remain the same, and more importantly, this includes any distortions.

Except that I’m reasonably confident that it is not wrong, in the point that the only difference in what you will get with the lens when using it with different sensors is only a crop/fov difference. Everything else will be the same.

Yes, with the sole exception of field-of-view, a 50mm on a hassy is the exact same thing in terms of rendering and distortion as the same lens on a m4/3.*

* It is also very likely that I am wrong, I am only relying on some simple engineering logic to come to these conclusions. I am thinking that if we set up a camera obscura type device, with only a lens and a viewing screen, the size of the viewing crop on the screen will have no impact on the lens characteristic other than to show less (or more) of the resulting image (crop). Right? Distortion and rendering will remain unchanged.

I agree as well! I am only pursuing this topic in hopes of finding a nice way to clarify some of these things for others to better understand. :smile:

[edit]
What we need is a way to purchase an FF and crop in a system with the same lens for all of us to loan out as needed so we can test these things. pixls.us hardware lending library! (Oh, and I guess we could shoot some photos with it as well occastionally… :smiley: ).