ON FF camera preferably; set the focus to manual and turn IS off, focus at infinity, ( and later at the nearest focussing distance to comare) look through the VF through well back-lit frosted glass or similar (e.g. toilet window - doesn't have to be very bright light but good daylight) and just zoom from 70 through to 200 whilst looking through the VF
Notice the ring of light zoom back and forth???



:roll
