[Leica] 400mm f6.8 Telyt problem

[henningw at archiphoto.com (Henning Wulff)]

At 9:49 PM -0500 1/12/07, Leonard Taupier wrote:
>I tried a 400mm f6.8 Telyt lens today. The lens was mint as was the 
>R8 I tried it on. The problem I had was it would not focus all the 
>way to infinity. This was visible in the viewfinder as well as on 
>film. I would say the focus was fine up to about 500 meters. Has 
>anyone run into this problem? it appears that if the sliding focus 
>was allows to come towards the body another 1/8th inch or so it 
>would be fine. As neither the lens nor the body were mine I didn't 
>attempt any adjustment to the infinity stop.
>
>This lens is very nice otherwise and includes the shoulder brace and 
>original instructions in the original box for less then US $600. The 
>photos of closer focused objects look pretty sharp.
>
>Len

This is a guess, but....

The front lens assembly is held in a unit that unscrews from the rest 
of the front barrel. The final location of the front lens unit, which 
will determine whether it can focus only on nearer objects, to 
infinity, or past infinity, is determined by a spacer ring that this 
front lens assembly screws against. This ring is machined at the 
factory to match the individual lens, as the lenses are not all of 
exactly the same focal length.

So it could be that the spacer ring is not seated correctly, because 
if it is slightly askew, it could seem that the front element is 
seated firmly while not being in the right position, ie, not screwed 
far enough in. Or some foreign object could be in the way, preventing 
correct seating. Or, and this is a lot less likely, a spacer ring 
from another lens was mistakenly inserted.

In any case, the first thing to do is to unscrew the front element 
assembly, shake out the spacer ring and reinsert it after making sure 
no foreigh object is in the way, letting it fall in smoothly. Then 
screw in the lens assembly again and check focus. Most likely the 
lens will now focus to infinity.

If it still doesn't, the spacer ring can be ground down until the 
lens does focus to infinity.

BTW, $600 is somewhat on the high side.

-- 
    *            Henning J. Wulff
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