Hi--

>I know this is a problem that has nothing to do with the Nikon you sold me.
>I posted this on the Nikon mailing list. I was wondering (since you
>probably have a lot of F3 experience) what you thought about this
>interesting problem I am having.
[Joe ]
>>I have a new F3/T and a new Tamron AF 24-70 mm F/3.3-5.6 lens. Whenever I
>use the lens at its 24mm setting, my mirror stays up in the Nikon. Then
>when you turn the zoom ring away from the 24mm setting towards the next
>longer focal lengths, the mirror comes down. It only takes a very small
>turn of the zoom ring to accomplish this. I looked at the camera end of the
>lens and indeed the inner barrel of glass protrudes the longest towards the
>mirror at this setting, but I can't believe that this part of the lens
>protruding into the camera body is mechanically "hitting or interacting"
>with the mirror to prevent it from coming down. Does this make sense?
>>
>>I don't see any marks on the back of the mirror or on the camera-end of
>the lens that show any wear or scratches indicative of a mechanical rub or
>interaction. Of course, this has only happened no more than 10 times.
>>
>>I read the Tamron manual and it mentions nothing of this, of course I have
>not called them yet.
>>
>>Will this ruin my mirror and camera? Could my mirror or mirror alignment
>already be ruined? Should I sell the lens? How could Tamron afford to make
>a lens that would cause this effect on a popular camera?

I would NOT use this lens on any F body - it appears to have a defect that
either prevents the auto-diaphragm actuator lever from moving, or the
mirror passes on the up-swing (more spring tension there), but catches on the down-swing (sharper angle of hit, less spring force - look for slight marring of paint on the front edge center of mirror, or very top edge
of lens rear section [when at 24mm]). the F3 mirror is long (to prevent image cut-off with long tele lenses), and the Tamron (intended for newer,
amateur-design cameras) probably extends too far back in your sample
(um, I would be inclined to use a better lens on that body, anyway...;-).
The F3 is solidly made, but mirror alignment is easily disturbed. To check
it (photo repair places won't do it well...), put on a known, good lens. Check infinity-focus correctness. Focus carefully on a distant, contrasty subject at first one edge, then the other, then top center, then bottom center - while noting the focus position marking on the lens (MF lenses
are better for this (and most other things...;-) - it should be the same (some focus error on your part is inevitable, but doing it several times
to come up with an average at each location should work). If you find
errors, try another lens (this type of focus error is comon in lenses - especially zooms). If all is OK, then take 4-5 frames on film of a
newspaper at a 45 degree angle, noting where you actually focused. Check
the film with an 8-10X magnifier to see if the average is correct (there will be some variation). Good luck! (Chances are all is OK, especially if
infinity-focus is correct with several lenses [lenses do vary a touch
in infinity-focus correctness, though...].)