most APSC lenses, e.g. tokina 12-24, tamron 11-18, sigma 10-20 can be used on Full frame cams from a certain focal length.
but i read somewhere on bob atkins that these lenses were not 'designed' to be used on FF cams.
i don't understand this. why is it not 'designed' for FF? is it because APSC lenses have a lower resolving power that cannot match FF sensors?
anyone can explain?