Odd focus with random shutter press -200mm 1.8

[img]/ubbthreads/images/graemlins/confused.gif[/img] I am renting a 200mm 1.8 for a show this weekend and unlike the other five lenses I've used for 30K+ exposures, this one not infrequently but not always focuses to infinity when I press half-way on the shutter release. This has never happened with any other lens before (and is not happening now either with the other lenses). Odd -- I focus with AE-lock, not shutter release, and furthermore this happens even with lens in manual focus mode. Infinity is not the preset (though I am using the preset to bring me back easily). The simple answer is something is wrong with this lens -- but has anybody had this experience and is there something simple in the way to use this lens that I am missing (no manual with the lens)? Thanks.

[David_Pennybaker]

Does it STOP at infinity?

Goes all the way to the farthest the helical can bring the dial (was so busy thinking about getting the shots didn't look at the exact place on the dial)

[David_Pennybaker]

And then just stops there, right?

Do you perhaps have the focus switch set to 2.5m - 5m (or whatever that intermediate setting is) ?

The first thing I'd do is check that setting, and set it for the entire lens focus range.

it's been always set at 2.5m to infinity

[Walter_Kimmel]

It sounds like a lens problem. I would use a pec pad and eclipse fluid to clean the lens and lensmount contacts.


With my 100-400 lens, on occasion I found that the IS stopped working, only to discover that I had inadvertently brushed the switch into the off position while shooting. And on at least one occasion, I found that the focus range switch had been changed while the lens was resting on top of my shoulder bag.

I now have a small strip of Gaffer's Tape on each of the switches, and I haven't run into those problems again.

[KenPhillips]

And while you are at it, be sure to clean the little AF ports in the bottom of the mirror box ... if they pick up a dust bunny your AF will confound you!
Ken