JohanCruyff said:
Be aware that 85mm on FF have less distortion than 50mm (cropped) on APS-C.
I wouldn't use 50mm (neither on crop nor FF) for close-up portraits.
Distortion? THE prospect of 50mm APS-C camera is equal to 80mm on full frame, so the distortion PERSPECTIVE equals. The pincunshion distortion Sigma 50 Art, disappears in an APS-C body.
Sharpness in the center is a little better with Canon 85mm F1.8 in full frame. But Sigma 50mm Art in an APS-C body, has better contrast in the image corners, much better vignettes, and no chromatic aberration that affects 85mm F1.8.
Canon 85mm in full frame body
Sigma 50mm Art in APS-C body