Sorry if this a beaten-to-death subject. I did try a search but couldn't find the right keywords.
I had read that, if you use a FX or a DG lens on a camera which has an APS-C sensor, the image is "better" because the center area of the lens is more accurately made and there is less vignetting and less CA compared to a DX or DC lens. And it has been my own habit on both my SD10 and my D50 to use FF lenses for macro work and the kit lenses for outside snaps (I'm not a Pro).
Then, over on another forum, I read:
queried by:This is the classic case of re-using a lens designed for a larger format system. FF and APS-C get this all the time (lenses that perform well on FF often lack sharpness and contrast when mounted on APS-C: the 24L on Canon is a pretty stark example). You are magnifying the image more on the smaller format, which puts more "stress" on the lens, enlarging the aberrations. Unless the lens falls off into pea-soup territory near the edges of the frame with vignetting destroying all light collecting advantage, you will always get better results on the native mount.
Rebutted by:I would have thought that since an aps-c designed lens on m4/3 or FF lens on aps-c would be just as good since it essentially would be using the center of lens which typically tends to be a lens sweet spot in terms of contrast, sharpness, and overall IQ.
An interesting set of posts which could determine the fate of my Sigma 50mm macro DG lens currently attached to a D50 APS-C camera.This argument would be correct if you are comparing how many lines can be resolved per mm of sensor, which nobody does in real life. People compare resolution per entire image (width or height). With a larger sensor the lens can bring a larger area into play so the total number of lines that you can distinguish across the entire image height (or width) should be larger.
Unfortunately, the first and third quoteés are not really specific in their claims. So, lets go to extremes:
You have a FF camera and a 4/3" and just one mount-compatible FF lens. 24mm sensor height vs 13mm. Both sensors have 5um pixel pitch and the shot is of a 40mm object at 1:4 mag which is typical of what I do. Within these bounds, what do you think?
My thought is that there is no difference in image quality but the FF image would need a bit of cropping ;-)
So, are there other factors involved? Shooting distance? DOF?