I bought a Nikon D100 several months ago and like it a lot. The one problem it seems to have is that it tends to “hunt” in autofocus mode, particularly with telephoto lenses.
Any help on how to eliminate or reduce this annoyance without going to manual focus would be appreciated.
Is it annoying when you’re taking a picture, or just when you’re carrying it around? Mine does it too when I’m walking around with it. Putting the lens cover on it makes it give up pretty quick, and it’s easy to take it back off.
Hope this helps.
I keep it turned off when not shooting. The shutter release needs to be partially depressed to focus.
What do you mean “focus hynting”? You mean the camera is trying to focus all the time?
If so, try FOCUS OPTIONS->Auto-Focus Mode and select Single AF.
That’s on my 5700 Coolpix, so the menus in the D100 might be different.
Many cameras will do a focus lock when you half-depress the shutter.
If the shutter is completely depressed, it might need therapy to achieve focus.
Usually this depends on the autofocus setting: In “single” mode, when you half-depress the shutter it finds the focus and lock to that point. “Continuous” mode will try to focus continuously while the shutter is half-depressed, so it can follow a moving target, for example.
If the OP means the camera has trouble finding a focus at all, the only thing I can suggest is to use the single focus mode and find a high-contrast feature to focus on. (Autofocus works optically, so it can only focus on sharp edges and other sharp, high-contrast features on the target.) Once it locks on, keep the shutter half-depressed while you compose the picture, then press all the way to take the picture.
This is often a problem in low light or in low-contrast scenes, and it can be worse with particular lenses. I don’t think there are any easy solutions, other than only taking photos of high-contrast scenes in good light! Or you could try different lenses, see which focusses best.
I find the problem from time to time when taking macros (D70, micro-nikkor 60mm). It’s invariably a contrast problem.
I assume your AF assist light is on? I guess if you’ve turned this off for some reason AF could be a bit buggered.
I don’t have a D100, but it’s film cousin the N80. As others have mentioned, the two big factors on whether you can get a focus lock are the contrast and available light.
Most of the lower-end zoom telephotos have a very slow (higher number) aperture. This doesn’t give the AF sensors much to work with. For example, my slowest (and cheapest) lens, the 70-300, has an aperture of 5.6 at 300, and even in moderate light it will cycle from its closest focus to infinity a number of times before giving up. Add to this the long throw, and the lens is almost useless for AF. I usually just manually focus and hope I got it right.
The N80, and I assume the D100, only look at areas of vertical contrast to focus. If the scene has many high-contrast vertical lines, the camera will have a much easier time finding the focus. Some of the more expensive bodies with better focusing modules will look for both vertical and horizontal contrast.
The focusing motor on the N80 is slow, and I’ve heard the same complaint about the D100. This shouldn’t really affect the ability of the camera to lock on a focus, but sure adds to the annoyance when it’s trying. One work-around is to use the AF-S lenses, which have the AF motor built into the lens. The AF-S motor is much faster than the motor in the body, and also very quiet. At the other extreme from the 70-300 is the 17-35 AF-S IF 2.8, with a very short throw, fast motor, fast aperture, even when it hunts a couple of times it’s done before I’m ready to open the shutter.
Make sure you have it in single-servo mode, with the center focus area selected. The center area seems to be the most sensitive.
D100 owner here. The camera has a good autofocus module but I don’t find it as fast and robust as the true pro digicams like the D1H. The only thing I can add to what others have said is to take active control of which focus point is selected for a given shot. I can usually see the shots out of focus are my fault, usually back focus because the critical subject didn’t cover the default center focus point.
Another D100 owner checking in.
I’ve had many of the same issues. I’ve found that the metering mode has an awful lot to do with that, for some reason. It seems to hunt most when it’s in matrix mode, and much less in spot mode. I never use center-weighted, so I can’t speak about that.
I’ve found that for my purposes, I usually just meter off a mid-range neutral tone and hold the exposure with the AE-lock button. Seems to work pretty well, at least for shooting in straight manual mode.
Alternately, I’m guessing you could change the button to only AF-lock if you’re shooting in aperture or shutter priority.
my $.02 anyway
Thanks all. I suspected a contrast problem, and you’ve confirmed it. Even with the Nikkor F2.8 80-200, it does this at the top end when shooting distant scenes such as mountain/sky/ocean where the contrast is minimal.
Oh, and very funny, Finagle. 
Does your 80-200 have a switch to disable the macro feature? It might help a little bit. It limits focus range, so the camera can “hunt” through the focus range faster.