I’m still trying to make up my mind as to which DSLR to buy. I long ago decided on Canon, and the Rebel’s a little small and a little too low on the megapixels for my tastes. In my price range, that leaves the 50D and the 5D Mark II (or equivalent older models, but I like newer toys. :-) ). The primary difference between these two are:
The 50D is an APS-C sensor with a 1.6x Field-of-view crop. The 5D is a full 35mm camera.
The 5D has 21 megapixels vs. 15 megapixels on the 5D.
I like to take pictures of two things: birds and bugs. (For family, friends, and pets I can use a point-and-shoot.) Keeping that in mind what makes sense?
The smaller sensor on the 50D means that the image is cropped and you get a closer picture. (These are really two sides of the same coin.) Whether this is a good thing or a bad thing depends on what you’re shooting. If you like wide-angle landscape shots, you hate the cropping and buy the 5D, but I take pictures of birds and bugs. For birds, you want the crop, but only if the megapixels are the same size. That is, a 15MP APS-C camera will outperform a 15MP full-frame camera. However the megapixels aren’t the same. What does that mean?
In essence, set up side by side with the same lens, and pointing at the same bird, the full frame 5D will pull in more background than the APS-C 50D because it has a wider field of view. That’s great if you don’t lose megapixels on the bird. Do you? Let’s do a little math.
Let’s assume we’re looking at a Sanderling far enough away that it fully fills the frame on the APS-C sensor. At maximum resolution, the Sanderling will be 4752 pixels wide and 3168 pixels high (honestly less because sanderlings are wider than tall, but assume a rectangular bird.) By contrast on the 50D we’ll have 5616 x 3744 pixels, but with the same lens not all of those will be focused on the bird. How many bird pixels do we lose? If we end up with 4752 by 3168 bird pixels or more, then the 5D makes sense. But if we end up with fewer than 15.1 mega-bird pixels, then I should prefer the 50D. (Of course I could just screw a 2X extension tube onto the 50D, but where would the fun be in that?)
The 5D and the 50D will both place the bird on a sensor of 22.3mm * 14.9mm. That’s 100% of the 50D’s sensor, but only 22.3mm * 14.9mm / (36mm*24mm) == 38.46% of the 5D’s. So where the 50D is using 15.1 megapixels for the shot, the 5D is using 38.46% of 21 megapixels. Thus side by side with the same lens at the same distance the 5D only gives me about 8.1 megapixels, barely more than half of the 50D’s. Thus to take pictures of birds I should definitely prefer the 50D.
Check my math. Does that make sense?
Anyway, this is all for the birds. For the bugs, especially ones you can get close to, I think the full frame just works better. In that scenario, (1:1 macro) it’s a straight calculation that larger pixels are better and larger sensor sizes are better. But wait a minute: the 5D has a much larger sensor (256% larger) but only 35% more pixels. What does that imply about pixel size?
Another quick calculation and we find that on the 5D we have 5616 * 3744 pixels/(36mm * 24mm) = 24,336 pixels/ mm2. Assuming square pixels, each pixel is 1/24336 == .000041 mm2. On the 50D we have 4752 * 3168 / (22.3mm * 14.9mm) == 45,307 pixels/ mm2. Thus each pixel is approximately .000022 mm2. Larger pixels are better (less noise) so indeed it does look like the 5D handily beats the 50D by this measure.
Quick summary: shoot birds with a 50D and bugs with a 5D.
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