« on: January 30, 2013, 10:20:26 AM »
This is one of the best questions asked in a long time. I come from film myself and started out with a 30D (140 000 exposures taken), 70-200 /4 L IS and 17-40 /4 L.
Now I have a 5D mkII and I am very happy with that camera.
As you have noticed, at low ISOs cameras these days all look great. As has been said, IQ differences comes into play in more extreme situations. But there are other things that matters to your final image and that is how lenses behave on each camera.
On a full frame camera the lenses behave as they used to do on film. That is, f/4 gives a rather short DoF (yes I know, focal length, subject/background distance). I think of it as f/4 on FF is approximately f/2.8 on crop. That means you get less DoF at the same apeture and framing. That also means that for portraits the FF has an advantage for bluring backgrounds, but APS-C has the upper hand on sharp landscape shots with everything in focus. You would think that you can stop the lenses down even on FF to get a large DoF and while you can do that, diffraction will set in earlier compared to APS-C (I think). You also get the greater compression of for instance the 85mm lens on FF compared to a 50mm lens on APS-C, giving more flattering portraits.
Also, the 650D has no AFMA so there is a chance of having to send camera and lenses to Canon to get them all adjusted for maximum sharpness. Sometimes that is important - the need for 100% focus is much greater whit the high resolutions we have today. It is much harder to get a 100% sharp photo with the 5D mkII compared to the 30D I think.
There are great wide angle lenses for both formats, but to get greater reatch the tele lenses get more expensive if you are unwilling to crop in post.
The autofocus of the 5D is more capable than the 650D making it more suitable for action.
To me another thing is important - larger and brighter viewfinder: this is a big plus to me! It´s easier to use and feels better after a long day of shooting. Also I like that I can use my 5D mkII with my mittens since I live in Sweden and I don´t stop photographing in the winter. I don´t want a smaller camera body.
So what do you need?
If you want to do portraits, extreme low light, more action, shallow DoF, adjust focus on your lenses? Keep the 5D.
If you want to do landscapes? Keep the 650D.
But yes, both cameras are capable and they both are great imagecreating mashines. The difference is in the format and how that affect the image, not really the image quality itself.
I hope this helps you.
And don´t forget how to use your tripod!