question reagarding perspective distortion on ff vs crop

Qarik

say I am shooting a portrait with 50mm on FF and 50mm on crop. To achieve the same framing on both I have to be closer with the FF. My question is, is the perspective distortion the same in both cases? My 1st intinct is to say no..they will be different.

ziggy53

Qarik wrote:

say I am shooting a portrait with 50mm on FF and 50mm on crop. To achieve the same framing on both I have to be closer with the FF. My question is, is the perspective distortion the same in both cases? My 1st intinct is to say no..they will be different.

Using the same focal length on 2 different formats and framing the same view, of course that will change the geometry of the situation and, by definition, change the perspective. Without examples I cannot claim that there would be perspective "distortion", but the perspective would certainly change with the changing "vantage".

Nikolai

They will be different, because while focal lenth is identical the distance to the subject has changed.

craig_d

Assuming for the moment that we're only talking about rectilineal lenses, not fisheyes or more exotic types, the only thing that changes your perspective is your physical position and orientation in space.

Aside from resolution, a crop-frame shot is equivalent to shooting full-frame with the same focal length and aperture and then cropping the image proportionally on all four sides. This is in fact what the camera is doing by virtue of having a smaller sensor.

Similarly, the difference between one focal length and another, again ignoring resolution, is just a matter of cropping. If you take a shot at any given focal length and then crop off the sides proportionally, the view will be equivalent to that of a longer lens.

Qarik

craig_d wrote:

Assuming for the moment that we're only talking about rectilineal lenses, not fisheyes or more exotic types, the only thing that changes your perspective is your physical position and orientation in space.

Aside from resolution, a crop-frame shot is equivalent to shooting full-frame with the same focal length and aperture and then cropping the image proportionally on all four sides. This is in fact what the camera is doing by virtue of having a smaller sensor.

Similarly, the difference between one focal length and another, again ignoring resolution, is just a matter of cropping. If you take a shot at any given focal length and then crop off the sides proportionally, the view will be equivalent to that of a longer lens.

This makes sense..though I had to give it a few minutes of thought to fully convince myself.

paddler4

Check this out:

http://www.bobatkins.com/photography/technical/digitaldof.html

craig_d

paddler4 wrote:

Check this out:

http://www.bobatkins.com/photography/technical/digitaldof.html

Atkins is talking about DOF there, not perspective, so it's not directly relevant to the original question here.

Even for DOF, his presentation is kind of misleading, at least to the less-technical reader who may not realize the significance of some of the assumptions he states. There are different comparisons that can be made between FF and APS-C cameras, but none of them are really apples-to-apples because you can't take "exactly the same picture" (camera in same position, same focal length and aperture, same framing) in both. You have to change position or focal length if you want to maintain the same framing (and he assumes you do want that), and that change is actually what alters DOF.

LiquidAir

The perspective is determined by how far you are from your subject. As long as you stay the same distance from your subject the perspective will be the same no matter what lens or sensor you use.

Now if you fill the frame with a 50mm lens, you will be closer to your subject with a full frame body than you will be with a crop body, so the perspective changes as the distance changes. However, you stay at the same distance and crop in post (or change to an 85mm lens), then the perspective will be the same.

Tim Kamppinen

As others have said, perspective is determined solely by the distance from the camera to the subject or whatever other objects are in your frame. If you get too close to a human, the features that are closest to the camera will become exaggerated because of the perspective... i.e. noses appear larger, as well as forheads if you're shooting at a downward angle, hands and feet that are closer to the camera than the rest of the body, etc. We call this "distortion" since things appear to be out of proportion, but it's a totally different thing than lens distortions (such as barrel or pincushion, etc.) An optically perfect lens with no distortion whatsoever would still produce comically large-probocised images of people if you got right up in their faces with it.

Of course wider lenses force you to get closer if you want to fill the frame, and shooting on full frame makes your lens instantly wider than if you were shooting on a DX camera. It always bugs me when I hear people talk about how "wide angle lenses distort people," however, because it's not really true. Standing too close to someone and taking their photo distorts them. If you stand at a reasonable distance wide angle lenses are just fine for things like group shots where you are filling the frame not with one person but with a bunch of people, or for things like environmental shots that show a larger context without filling the frame with the subject.