Working in a chemical factory we often calibrate the instruments.
We calibrate in 10% increments over the range of the inst on critical Inst and 25% increments for quick standard cal check. Hysterisis must be well controlled with all the cardinal points within tolerance - usually 0.5% or less.
When checking my zoom lens 24-105, 70-200, 100-400 I find they all Rear focus at the short end and front focus at the long end. To the extent that there is no happy medium. I can't have the focus window sorted at 2.8 or F4-4.5 at both ends of the zoom meaning I lose a degree of sharpness somewhere unless i stop down.
My question, what good is a 2.8 lens if you cant' have it sharp at both ends of the zoom? I pay a premium for it but it doesn,t actually work.
Whilst I accept there are tolerances is it too much to ask Canon to calibrate their lenses at various points accross the zoom range before they ship them, or do they do this already? Is it possible to do it, yes-no?
Frustrated but off my chest now.
Any thoughts on the matter?
Cheers
