Cropping vs. Zooming (equivalence question)

[ehud.eshet]

Hi all,

Let's say I take a snapshot using Canon 600D with EF 50mm f/1.4.
Then, I crop it to 2592 X 1728 pixels (1/4 of the original 18MP) using computer software.

Now let's say I set the Canon 600D to capture snapshots with same (2592 X 1728) resolution and want to get similar results.
Should I use a EF-200mm f/1.4 (I know there is no such lens) to get the same framing and exposure?
What should be the equivalent lens in terms of DOF?

Thanks.

 

[NormanBates]

what you're doing in the example you describe is turning your 1.6x crop factor camera into a 3.2x crop factor camera

therefore, the equivalence you're looking for is the following:
* in terms of FoV and exposure, 35mm f/1.4 on 3.2x crop is equivalent to 70mm f/1.4 on 1.6x crop
* in terms of FoV and DoF, 35mm f/1.4 on 3.2x crop is equivalent to 70mm f/2.8 on 1.6x crop

therefore, you get exactly the same picture, in terms of FoV, exposure and DoF, with these two options:
* 35mm f/1.4 1/60s ISO 100 on 3.2x crop
* 70mm f/2.8 1/60s ISO 400 on 1.6x crop

see test here:
http://www.similaar.com/foto/doftest/doftest.html