problems with Nikon 70-210 AF

[Matthew Harrington]

I just purchased a Nikon 70-210 f/4-5.6 AF zoom and am
worried that it needs some repair. The pictures are
fine, the problem is with the focusing. When focusing
(in AF) on something like the horizon, the lens zooms from
infinity to close range, and back to infinity, indicating
that it is having trouble locking on to something on which
to focus. My 50mm f/1.8 doesn't have this problem, it generally
focuses much more accurately. The real problem is that when
returning to infinity from close range, the image comes
into focus at infinity and then gets slightly blurry. What
is actually happening is that the lens goes slightly past
infinitity when turning the focusing ring to the right.
So, when shooting landscapes, I always have to use manual focusing,
which I dislike on this lens because when I turn the polarizer,
I usually turn the focusing ring also, blurring the image.

Can anyone help me? Does it need work, or is it just inherent in
the sliding aperature design (f/4-5.6)?

Thanks,

Matt H.

--
Matthew B. Harrington Internet: ma...@ucsd.edu
University of California at San Diego Bitnet: MATT@UCSD
9450 Gilman Dr. 926067 UUCP: ucsd!matt
La Jolla, CA 92092-6067 Tel: (619) 457-9884

[David Jacobson]

In article <13...@sdcc6.ucsd.edu>, mbha...@sdcc13.ucsd.edu (Matthew Harrington) writes:
> I just purchased a Nikon 70-210 f/4-5.6 AF zoom and am
> worried that it needs some repair. The pictures are
> fine, the problem is with the focusing. When focusing
> (in AF) on something like the horizon, the lens zooms from
> infinity to close range, and back to infinity, indicating
> that it is having trouble locking on to something on which
> to focus. My 50mm f/1.8 doesn't have this problem, it generally
> focuses much more accurately. The real problem is that when
> returning to infinity from close range, the image comes
> into focus at infinity and then gets slightly blurry. What
> is actually happening is that the lens goes slightly past
> infinitity when turning the focusing ring to the right.
> So, when shooting landscapes, I always have to use manual focusing,
> which I dislike on this lens because when I turn the polarizer,
> I usually turn the focusing ring also, blurring the image.
>
> Can anyone help me? Does it need work, or is it just inherent in
> the sliding aperature design (f/4-5.6)?
>
> Thanks,
>
> Matt H.

...

1. The manual that comes with this lens specifically states that this
lens will focus past infinity. This is not a problem.

2. Are you using a linear or a "circular" polarizer. If linear, that
is almost certainly the problem. You don't say what camera you are
using, but I'll assume its not too different from an 8008. The
instruction book for the 8008 says it won't work with a linear
polarizer.

3. Horizons are hard for Nikons. They just have a horizontal sensor.
But there is little or no horizontal detail in a horizon. Try tipping
the camera 45 or more degrees. You might still have problems if the horizon
is obscured by haze. You need something with sharp contrast.

4. Any f/4 or f/5.6 lens will have poorer autofocus performance than
an f1.8 lens. At full aperture it has more depth of field than the
f1.8, so the AF sensor has a harder time getting it right.

5. If anything is broken, it is your camera, not your lens.

-- David Jacobson

[Alan Stewart]

mbha...@sdcc13.ucsd.edu (Matthew Harrington) writes:

>So, when shooting landscapes, I always have to use manual focusing,
>which I dislike on this lens because when I turn the polarizer,
>I usually turn the focusing ring also, blurring the image.

My Nikkor 33-70 F3.3-4.5 does similar things when it tries to focus on
something at infinity. If there is no definite object to focus on, even at
infinity (like a house etc in a landscape), the lens continually focuses
and the image becomes blurred. I then have to use manual focusing.

Use only the Single focusing setting, rather than continuous. This can
help, however, I think your problem is normal for Nikkor AF lens.

Alan
Sydney

[Eric Thomas SUNET]

But does the camera say X or O? If it can't find something to focus on (and
the slower the lens, the more likely it is), it may indeed start "scanning"
the whole focusing range. Not finding anything, it should stop with an X
(unable to focus) status at one of the two extremes; if this is what happens,
it is a bummer of course but it's not really "abnormal": the camera is just
giving up and telling you that you'd better switch to manual mode. As to the
area to the right of the infinity mark, it's because the exact location of the
infinity setting might vary according to temperature.

Eric