Originally posted by ismaelg Thanks Lowell,
When checking on focus accuracy, does it makes any difference to try different focal lenghts? or is that irrelevant as long as it is kept constant?
Thanks,
I would try at least both ends, maybe one middle focal length.
As I said above, you should do this with real scenes, not targets, and evaluate based upon what you have focused on.
Your focus target should be relitively flat, to give the lens and camera the best chance of finding correct focus. Focusing on a sloping object will introduce errors since you are never quite sure what the sensor sees. your target surface should be bigger than the focus sensor location dot on the screen. For scenics, use a building wall or other flat surface in the middle fo the frame, for close up stuff, pick a typical subject but again try to have the focus sensor location dot over a flat surface.
I have never tried doing side by side tests like this with an AF lens, I have done it with MF several times to compare different lenses I have,