Nikon N80 autofocus issues

[jokola]

I have a Nikon N80 and a Tamron 28-200 XR as my main setup. It's been acting weird lately. When I first turn the camera on, it seems to autofocus fine, regardless of lighting, distance to subject, etc. After about 45 minutes of on-again/off-again use, the autofocus seems to hunt more and more, even in outside lighting but more so if indoor lighting is even slightly dim. It seems more of a problem if the subject is far away, or if the lens is extended out more than about half way. The center focus area gives slightly less trouble, while the far right seems to hunt much more. The last shoot I did was of a large group of people maybe 15-20 feet away on a bright, overcast day, and it just would not focus. I switched to my Nikon N6006 with a Sigma 28-105 and that was just fine. Later that day I switched back to the N80/Tamron and it seemed to work OK for awhile. Then again after 45 minutes or so, it hunted like crazy on a group of people in overcast/sun. It seemed to settle down, but the people at the right edge of those pictures are blurry (out of focus) even though subjects on the same plane at the left edge are fine.

Today I put a variety of lenses on the N80 (Tamron 28-200XR, Nikon 50mm 1.8, Sigma 28-105, Tamron 70-300) and it seemed to autofocus OK with them all when the center focus was selected but less well when the right or left focus was selected, especially with the Tamron 28-200 but also sometimes with the Nikon 50mm. Then I put all the same lenses on the N6006 and at first they all seemed to work fine, but then the Tamron 28-200 seemed to hunt more and more on the N6006 although the others were fine.

I plan to switch to digital soon (Nikon D70) but I don't know if I should try to have any of this equipment checked. I would keep the lenses, except maybe the Sigma, but I wouldn't want to sell or give away the bodies if something is wrong with them.

The Tamron 28-200 is still under warranty but I am not sure what that is worth... I bought it in April 2002.

Oh yes, I put fresh batteries in the N80 before each of my last two shoots but they were a different brand than I've used before.

Where should I start?

THANKS!

[schuchmn]

Hmm. Strange.

Two things strike me -- one is that the problem doesn't occur to start with but develops later. The other is that subjects in the same plane are not all in focus. I wonder if the lens has a loose element.

Another thought is this -- the Tamron has a max aperture at 200mm of f5.6 which I think is the limit of what Nikon specs the N80 autofocus sensors to. And all lenses show some light fall-off off-center and so the outside sensors may be getting only marginal light for autofocus. So if the body has an AF problem or if the light was a little low or the subject lacked contrst, the problem would likely be at its worst with that lens.

All of which tells us that it might be the body and it might be the lens, which is what we already knew. I think you need to try switching lenses and bodies in a controlled way (if you haven't already done so). When the problem occurs, switch the Tamron to your other body and put another lens on the N80. See if the problem goes with the lens or with the body. The key here is to make sure that you're experiencing the problem first. Also, find a subject that's big and flat and has detail, like a brick wall. With the camera on a tripod and carefully levelled, see if you can reproduce the one-side-out-of-focus problem.

Intermittent problems are the toughest ones to diagnose. One thing wasn't clear in your post -- when the problem occurs, what makes it go away? What do you do when it happens -- do you put the camera away until the next day? Does it work OK the next time out?


Regards
Dennis

[jokola]

Thanks for your reply. I haven't had a chance to do any real side-by-side comparisons. I did switch lenses and camera bodies around at home in a medium dark room, just to see under which circumstances the AF would "hunt" more than others. It does seem that the 28-200 lens seems to give more trouble no matter which camera body it's on. But it will be a week or two before I have time to actually put film in the two cameras and then do a more scientific test (and actually write down, frame by frame, what I did so I can look at the results in print.)

At the two events where I noticed the lens giving me trouble, here's what I did. The first event, I thought it must be me, and kept trying to make the camera autofocus on the subjects, which was frustrating and took a long time before it would work. After a few minutes, I took the subjects outside and by the time we had set up again, it was probably 15-20 minutes later and it seemed better. But of course it was also lighter outside! And it wasn't perfect, and certainly not as good as all my previous times using the lens.

The second event was pretty much all outside on a bright but overcast day. The first hour or so the camera had no trouble with AF. As soon as I noticed it starting to hunt and not snap, I switched cameras and turned that one off for about 20 minutes or so. I can tell you that there were a lot of subjects in the picture so I was pretty far away at that point and the lens was extended out some. When I turned the camera back on, it seemed to be OK for another hour or so, including inside a dark barn, but started giving me trouble again when I set up another bigger group shot outside where again I had to go pretty far away. Those last couple frames were pretty much useless on the left edge. I will try to scan one of those prints and post it later on to see if it yields any clues.

Thanks and I will keep you posted.

Jennie