@rosyjazz wrote:
I am considering a lens for my 500d. Its an efs 17-85mm. However, the seller says "At full zoom (85mm) the autofocus sometimes has trouble locking on to the subject."
Your thoughts?
The 17-85 is not a "constant aperture" zoom lens. I.e., its maximum aperture decreases as its focal length increases. Since autofocus works better at larger apertures, it may not work as well af full zoom, where the maximum aperture is smaller. Outdoors on a bright day that may not matter; in a dark room it very well might.
BTW, if it appears that I have the same problem, ignore that. I accidentally hit the "Me Too" button, which is much more prominent than the "Reply" button.
Bob
Philadelphia, Pennsylvania USA
