Question: I recently bought my first full-frame DSLR, a Canon ESO 5D Mk III, and find that I cannot fill the frame with distant competitors in sports photography when using my EF 70-300mm IS lens. I want more of a telephoto effect with this large-sensor camera, similar to the focal length magnification effect that I got with my EOS T3i. Is it a good idea to crop the photos with software? Wouldn't that give me the same effect as I got with the T3i when using the same lens?
Peter's Answer: Yes, cropping an image made by a camera with the 24x36mm sensor can provide the same effect as the field of view crop produced by cameras with a smaller sensor. After you finish cropping, less of the scene is included in the photo, so the primary subject does appear larger. But by extensively cropping a photo, you will be discarding millions of pixels, so the image will be smaller: with less resolution (or fewer megapixels). This concept applies to any full-frame camera of course, whether it provides 12, 21, 24 or 36 megapixel resolution.
The sensors used in most DSLRs are smaller than the full-frame 24x36mm chip, producing a field of view crop (sometimes called focal length magnification): the sensor records less of the subject's surroundings. You can achieve a similar effect by cropping an image made with a full-frame DSLR -- as I did in this case -- but excessive cropping significantly reduces the size (resolution) of the image file. (c) 2013 Peter K. Burian
The more you crop an image the smaller it will be (with less resolution). Of course this is less of a problem with your 21.1 megapixel camera than it would be with the 12 megapixel EOS 5D (or for a Nikon owner, with the 12 MP D700). If you do not plan to make a print larger than 13x19-inches, even a 10 megapixel image (roughly 30 MB is size) of high quality should allow you to get excellent results. And in my experience, that is the largest that most photo enthusiasts make or order.
If you often need oversized prints, or very high resolution images for another purpose, you should buy a longer lens so you won't need to discard pixels when cropping. But if that's not practical because of the cost of a 500mm or longer telephoto, you might consider renting one occasionally from a company such as LensRentals.com.
- Peter Burian teaches three excellent online photography workshops at BetterPhoto's online digital photography school:
-Boot Camp for New Digital SLR Owners
-Mastering the Digital Camera and Photography
-Mastering the Canon EOS Digital Rebels
- In addition, Peter's photography appears in two how-to books co-authored by Jim Miotke and Kerry Drager: The BetterPhoto Guide to Creative Digital Photography and The BetterPhoto Guide to Photographing Light.