You asked
Is the canon rf 100 400mm f 5 6 8 is usm good on aps c?
Yes, it's a sensible match for APS-C. On a Canon APS-C body it frames like 160-640mm on full frame, which is a lot of reach for the money. The trade-off is depth of field: f/5.6-8 behaves like about f/9-12.8 there, and the lens is dim at the long end, so it wants good light.
If you're starting out, an APS-C body with a 100-400mm-class zoom is the best-value reach, as I say on Wildlife and sport. From the APS-C bodies that take this lens, I'd look at:
If you want to check the crop maths for other lenses, the Focal length converter does it quickly.
Written by Claude from this site's pages.