On March 8th, I wrote:
"..... When using a Sigma 70-300mm and focussing at 70mm, the subject is not
sharp when zooming to 300mm. If I focus at 300mm (the subject is now sharp)
and I zoom back to 70 and focus again, the camera re-focuses and the subject
become unsharp again.... By the way, the problem doesn't occur when using my
Nikon 35-105mm."
First of all I would like to thank all of you that have taken the time to
reply to my F100 focus problem, posted last week. I subscribed to the
Nikon-digest just recently and have already learned a lot from its content.
Reading through the various replies to my problem, I extracted the following
explanations:
- it's not an F100 bug since the problem only occurs with the Sigma lens and
not with the Nikon lens;
- only use Nikon lenses on a Nikon camera (be careful though, as shown
hereafter);
- the refocusing can be caused by the variofocal design of the Sigma lens.
I did some more home work myself and besides my Sigma 70-300 4-5.6D APO and
Nikon 35-105 3.5-4.5D, I included more Nikon lenses such as the 80-200 2.8D,
the 35-70 2.8D and the new 70-300 4-5.6D as well as another F100 and a F90X
(the camera I had before) and discovered the following:
All the Nikon telezooms make both F100's refocus slightly when zooming from
the shortest to the longest focal length and pressing the focus button.
However at both ends focussing is sharp. My Sigma 70-300 acts similar except
that focussing at 70mm is NOT sharp! The other two zooms (35-105 and 35-70)
have less tendency to refocus (depending on the kind of subject) probably
because zooming between both ends with these standard zooms has a less
profound impact on "looking at" the subject than with the telezooms.
Mounting these lenses on a F90X really shows similar behaviour except that
now my Sigma works fine as well at 70mm.
So I agree that the problem is not the F100 but the Sigma lens which shows
signs of incompatibility with my F100. This also makes sense to me now,
knowing that (as you can read in the F100 instructions manual) there are
even quit some Nikkors that cannot be used with a F100 (I believe the TC-16A
has been discusses most in this digest). Since my Sigma lens has been
manufactured years before the F100 was launched but after the introduction
of the F90X, it could explain why it works fine on a F90X but shows problems
with a F100.
The salesperson at the shop where I bought my F100 told me that Nikon did
communicate some information saying that there are certain 3rd party lenses
that do not work properly with the F100.
I traded in my Sigma 70-300 and bought the (more or less equivalent) Nikon
70-300, so now I can fully enjoy my F100.
Personal lesson learned: Before upgrading to a another camera (in my case
the F100, but this is likely to be valid for any model, even from other
brands), make sure to test the compatibility with all your add-ons (BOTH
Nikon and 3rd party vendors) especially those bought years ago.
Thanks!
Toine Vermeulen
