Archived posting to the Leica Users Group, 2001/01/14
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At 10:56 AM +1100 1/15/01, Peter Zak wrote:
>Is Leica glass sufficiently well corrected for a focus shift to be
>unnecessary, as I don't see a IR mark on any of the lenses.
>
>If not, what is the amount by which the focus must be brought closer (I
>think?).
>
>Any experiences welcome....
>
>Best Regards,
>
>Peter Zak.
Generally, yes. The problem is that the focus shift is different for
different films and different filters. If you use HIE and an 87
filter (probably the most extreme case for general photography, set
your measured distance at about the nearer f/4 or f/2.8 mark on your
DOF scale (focus closer by the amount that the f/4 mark is different
from the infinity position). The newer the lens, the less correction
is needed. Don't correct for the APO lenses, or only very slightly
(f/2 mark at most).
Then, stop down to f/5.6 or f/8 if at all possible. These lenses
just aren't corrected for IR as well as for the visible spectrum.
For the Ilford 200 film, don't correct (and don't use the 87 filter).
The Konica film is only slightly more IR sensitive.
- --
* Henning J. Wulff
/|\ Wulff Photography & Design
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