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...