I was out shooting airplanes landing yesterday and it was probably nearly 100F or so outside.
I was using my d2x and a new 70-200mm VR, mainly at the 200mm range.
The first bunch of shots gave me no trouble with focusing, then about 20 minutes later, it stopped focusing like normal- it would get the focus, then -very quickly- refocus and the plane would be blury, then get the focus again and then refocus blury, and continue 'throbbing' back and forth.
This happened several times a second.
The focus indicator in the body wasn't giving me the circle during this period, it would just flash left and right focus indicators in sequence several times a second.
I tried: taking off my polarizer (heliopan circular), putting on a UV, turning off the body, taking off the lens and putting it back on, waiting a few minutes with the body off, changing focusing modes, etc, and there wasn't any difference.
Whether I tried to get it to focus at 200mm on airplanes or at 70mm on the grass 4 feet from me, it would do the same thing.
I first thought it might be getting faked out by the heat waves, but don't see why it would do the same thing to grass just a few feet from me with no visible heat waves.
I didn't have a second lens with me at the time, sorry. Firmware is 1.0b (the latest).
Could it have gotten over-heated? Possible lens issue?
Resorted to shooting manual.
#1. "RE: 'Throbbing' focus problem" | In response to Reply # 0BJNicholls Charter MemberTue 01-Aug-06 08:29 PM
Your headline sounded a lot sexier than the actual problem.
Are you saying the problem has gone away since this incident? If so, perhaps heat was affecting the AF system circuits. See if it happens again in the heat. If it does, you may need to send in both the lens and the body to have the problem diagnosed and fixed.