On 12 Jun 2003 11:49:54 +0200, Christoph Breitkopf
<chris@chr-breitkopf.de> wrote:
>Hello Brian,
>
>brianc1959@aol.com (brian) writes:
>> [focus drift of 4/200]
>I remembered David saying something about a different
>construction of the focusing mechanism in AI-S lenses,
>and after some googling found this:
><3de507d4.5976641@newsstand.cit.cornell.edu>
>
>Quoting him:
>> The AIS MF
>> were the best-made of all (except for the
"E"
>> versions), and tend to have the smoothest focus
>> with the least wear problems (two adjustable
>> hold-back pins are used in the focus-mechanism,
>> instead of one as in the AI lenses, helping to
>> keep things better-centered during focus, and
>> more easily adjusted after helical wear)
>
>Regards,
>Chris
Ah, that "dredged up" feeling...;-) And, my old
posts can be searched more directly at
www.nikonlinks.com/ruether/posts, though I have
not yet added the last year's "worth" yet...;-)
Internally, the AIS appear to be better-designed
than older lenses (and often include adjustments
to remove "slop" in the focus-ring motion that
can develop with wear), and they also, as Brian
noted, offer relatively fixed focus-ring position
with focus changes, unlike most other lenses.
For Brian: if you grab the front of the lens and
push/pull it relative to the rear, and there is
no motion (with the focus ring held still), and
the problem is only due to "auto-focusing" due
to the weight of the lens causing the focus ring
to turn, you can lock the focus ring with tape
(it takes only a couple of short strips of masking
tape to do it), or you can have thick lubricant
added to the lens focus helicals (the stiffness
of the focus can be from dried lubricant [leaving
gaps, which can allow the lens to move relative to
the bayonette even without focus-ring turning,
especially with worn helicals], from very tight
hold-back pin channel, or from wear-permitted
helical/hold-back-pin decentering/misadjustment).
The particular feel as the lens is focused can
often indicate the source of the problem...