Using an APS-C lens on a full frame camera is generally a bad idea, since you'll (generally) have extreme vignetting. Some full frame cameras can actually be damaged by having APS-C lenses attached Focal length is a physical property of a lens, so a full frame lens on an APS-C body will look the same as an APS-C lens of the same focal length.
The problem with APS-C's "real ecosystem" is that most of the good lenses have been developed for full frame. I shoot both DX and m43 and I really wish that a lens like the Nikon 200-500 had been
Buy now ($1,499): Adorama. aps-c APS-C cameras canon fujifilm nikon Photography professional cameras sony. These APS-C cameras prove that you don't have to drop crazy money on full frame cameras
Even with aps-c lenses, there could be an additional benefit. If you use other ratios than 3:2, let's say square for instance, you can take advantage of a larger area with a FF sensor than with aps-c. The difference would be important. But this requires to remove some parts of the lens.
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