How can I get the same image with the same 50mm lens on both FF and APS-C?

Question

First things first, I'm talking ONLY about framing here. No light sensitivity, no bokeh quality, no pixel quantity, etc.

A 50mm in a FF camera will give a certain composition and framing. How can I achieve the same composition and framing with a APS-C camera without changing the lens?

Will moving away from the subject will give me the same image? I know that zooming isn't the same thing as moving closer or farther from the subject, but will I be able to achieve at least a similar shot?

This video triggered this question. Check it out, it's very illustrating.

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EDIT: I know that a 35mm would give me the same shot in a APS-C. I want to know if this is possible without changing the lens.

Answer 1

In terms of field of view, or framing, APS-C is defined as a ratio to full frame. For Canon it's 1.6, for Nikon/Pentax/Sony it's 1.5. So, when looking at this:

X x 1.5 = Y

X is the focal length on the APS-C and Y is the focal length on the FF. So, we sub in and rearrange for:

X = 50 / 1.5
X = 33.3333

So, you'll get around the same field of view if the lens on APS-C is between 30 and 35mm. Now, if you're using the same lens, you'll have to use your feet. For APS-C, that means moving back and the distance will depend on the subject, but the perspective will change.

Edit For Updated Question

So, if the lens is the same...

As mentioned in both answers, the perspective will change as a result of changing position, so the essential answer is no, you can't when you're using the same lens. That leaves you with the last option I can think of: panorama. Several shots, 4 minimum I would think (2 top, and 2 bottom) would allow you to construct an image with the same perspective (or so very close that the difference is very difficult to detect) and same field of view. The drawbacks are obvious and include multiple images, must be a stationary subject, and more. Technically, however, it could be done given a suitable subject.

Answer 2

Yes you can acheive the same field of view and perspective using an APS-c camera, by shooting mutlitple images.

If your lens is something like the Nikon PC-E 45mm or Canon TS-E 45mm, i.e. they allow shift movements then you can get away with shooting three images in the opposite orientation like so:

To understand how this works imagine you are keeping the lens stationary and moving the camera with respect to the lens. You are effectively moving the sensor across the image plane, like how a flatbed scanner works.

Not only will you get the same perspective and field of view as the equivalent larger sensor, you will get the same depth of field too!

If you don't have a tilt/shift lens, you can get the same effect with 4 shots if you pivot the camera about the lens optical centre. Pivoting this way gaurantees the perspective doesnt change, despite the larger field of view as the camera does not undergo translation. Four images are now required to match the field of view exactly due to the bow-tie shaped image that results from shooting [rectilinear] panoramas:

Answer 3

Shoot with a 35mm lens. On an APS-C it gives an equivalent Field of View to a 50mm at FF.

Moving away from your subject means that you change your perspective. Your image will not look the same, although it will definitely allow you to fit (or frame) the subject in the smaller sensor.

@Matt Grum has a very nice example here.

EDIT After the question was updated: The short answer is no, it is not possible to get the same image using the same lens on different sensor sizes. As you could tell by now from the previous discussion, keeping everything else the same (that is, the focal length and the camera position) and changing to a smaller sensor is exactly equivalent to cropping your large sensor image in post-processing. In this case, moving away from the subject will give you the same composition of the subject in the image frame, but you will have a different composition of it with respect to the background.