About a year ago, I traded in my Canon EOS 7D for the Canon EOS 6D. The 7D is much faster, with a more complex focusing system and shoots 8 frames-per-second, compared to the 6D’s 4 fps. The 7D also has better weather sealing and a tougher body. So why would I “down grade”? I shoot primarily landscape and scenic photos, and the 6D has a full frame sensor, which uses nearly all of the “image circle” from EF-mount lenses. So my 17-40mm f/4L became a whole new lens on the 6D, because the angle of view on the 7D was 27-64mm, and on the 6D it really is 17mm at the wide end. Also, I love the shadow detail and better noise/high ISO performance of the larger sensor in the 6D. But while my 17mm lens has become a superstar, my 200mm lens has dropped from an angle of view of 320mm to… well, only 200mm.
I want to be sure not to confuse “angle of view” with “magnification”, because they are not the same. My 200mm lens on my APS-C sensor 7D had the “angle of view” of a 320mm lens on a full frame sensor, like the 6D. It’s not bringing the subject any closer on the 7D, the image circle coming from the lens is just getting cropped by the smaller sensor, which results in a narrower angle of view. And a 300mm lens has a narrower angle of view than a 200mm lens. So the 6D photos are showing more environment around a sports or wildlife subject, but the magnification of the optics is the same on both cameras.
Now here’s another thing to consider: The 7D had 18MP on a 22.3mm sensor, and the 6D has 20MP on a 35.8mm sensor. If you do the math, the individual photo receptors (pixels) on the 6D sensor are roughly 35% larger than the 7D’s photo receptors. This means they are better at gathering light and showing fine detail. The 7D was a fantastic camera which I got some amazing photos with, but the 6D renders images in a way it can’t match.
Put the last two paragraphs together, and the theory is: if I shoot at 20MP on the 6D and crop the image (using the 1.6x crop factor of the 7D) to get “closer” (compensate for having a wider angle of view), I could still have slightly better image quality. But there are a lot of variables involved. The tighter you crop, the more noise shows up, and ISO setting is going to affect this, even on a 6D with superior noise performance. Also, the tighter you crop, the more total resolution you loose, which means a medium to large print won’t look as good. You don’t need 20 megapixels for computer screen viewing (if you have an iMac with a 5K retina screen it’s nice), but printing the photo is different.
So after all that, here is an example of shooting a distant subject at 200mm on a 6D and cropping severely to isolate the subject.
Let me clarify, the image I’m posting is a 1500 pixels across JPEG export, not a full 20MP image. But it has not been cropped, so this is the full angle of view. For comparison, here’s a crop down to a mere 1.1MP.
This is obviously cropping MUCH more than a 7D sensor would, but you can see on a computer screen that detail is still pretty good, and noise is not a problem. But I’d certainly run into issues trying to make a large print.
Now a 300mm or 400mm lens would have gotten me more “magnification” AND a narrower “angle of view”, so I wouldn’t have to crop so much and I’d have a better end result for printing. Guess that means it’s time for an upgrade to a longer lens. I use wide angle lenses more often, but it’s nice to have that reach when you need it.