beavo451 said:
So if I wanted the extra stuff surrounding the birds, why don't I step back or use a shorter focal length? Typically, you would frame your photo as to how you want it in camera. I very rarely shoot a picture with the mentality that I will crop it in the computer.
You must have posted this while I was composing my reply.
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There are two reasons why APS sensors are cheaper than full frame sensors: yield (they're smaller, so there's a lower likelihood of defects in production); and the perception (right or wrong) that a full frame body is professional grade.
Over time, the yield issue becomes less of a concern. This is where the advantage of a 35mm sensor kicks in: it's easier to produce a sensor with a given number of pixels, because they'll be less dense on the sensor, with a corresponding reduction in noise and so on. A friend of mine who shoots with a 5D reckons that, for a given framing, it would whomp all over the D2X, for just that reason (I cannot judge, given that I don't have access to a D2X, nor to good quality glass for it ... I also don't have the experience necessary to do such tests properly).
People see the crop factor as an advantage for long-distance shooting, and it can be. But it's not a deal breaker because, even if you can't quite frame the shot as you want with the lens out as long as it will go, you can always crop the shot that little bit in post production. Professionals do that all the time. Try tracking a bird in flight with the framing set to fill the shot with the bird. You're not going to get the shot; you're better off to pull back a bit and crop the shot later on, because that makes it easier to get the entire body of the bird in the shot - which is the most important thing. At that point, the resolution of the sensor becomes important, which then gets back to the size and pixel density of the sensor.
The only time you'll get the framing spot on when you take the shot is when you have the time to compose everything properly. Even then, you'll be using a zoom lens, which immediately introduces a drop in image quality (remember that primes are always going to be better quality, and cheaper, than equivalent zooms), unless you're really lucky.
As I said: it's all about what you want to shoot, and what tradeoffs you want to make whilst doing it.