Can the Canon 7D's APS-C sensor match the 5D Mark II' full-frame sensor?
One question I often get asked about digital SLRs is what's the difference between a full-frame sensor (such as those in professional dSLRs like the Canon EOS 5D Mark II or Nikon D3S) and an APS-C-sized or "crop" sensor (such as those in most consumer-oriented dSLRs like the Canon EOS Rebel T2i or Nikon D3100, as well as higher-end cameras like the Canon 7D). And with semi-pro cameras like the 7D beginning to match or even better their big-sensored siblings specs- and feature-wise, it becomes an even more interesting question.
I recently came across the above video which helps provide one of the answers to just that question. Though "lens comparison test" is kind of a misnomer, this simple video (5Dmk2/7D lens comparison test from Mike Collins on Vimeo) offers a great visual illustration of how the difference in size between full-frame and APS-C sensors affects field of view (and focal length).
The video doesn't actually compare lenses as the title implies; rather, it provides a good depiction of how the field of view differs between the two types of sensors when using the same lens. Using the same set of prime lenses (ranging from 20mm to 100mm) plus a Lensbaby Composer thrown in for fun, Collins shot test videos with a full-sensor Canon EOS 5D Mark II and a APS-C-sensor 7D set up on a tripod in the same spot.
As the video depicts clearly, the larger sensor provides a much wider field of view when using the same lens. So one benefit of the full-frame chip size is that you can have very wide angle lenses -- thus, with a single lens (say, 28-105mm), you can get a good wide angle view as well as decent telephoto. But with an APS chip, the 28mm lens doesn't produce a very wide-angle shot, though you do gain a lot on the telephoto end. (For a good, in-depth explanation, read Bob Atkin's article on crop sensors and lenses.)
Of course the same number of pixels on a smaller size chip won't give you the same image quality as a larger chip, because in order to cram more pixels onto a smaller sensor, you need to use smaller pixels, which will results in more noise and less dynamic range, and therefore poorer image quality.
So the short answer is that, all other factors being equal, a larger full-frame sensor will give you a wider field of view and better image quality than a smaller sensor.
For more information, check out:
- BobAtkins.com: Crop Sensor (APS-C) Cameras and Lens Confusion
- DPreview.com: Sensor Sizes
[Via Gizmodo]