Re: [Leica] Focus Mark for Infrared Film.

[John Collier <jbcollier@home.com>]

> From: Peter Zak <pzak@desidero.com.au>
> 
> I know that the focus point for the use of IR film has to be changed - I
> don't see any such marks of any of my Leica lenses (35, 50, 90 Summicrons).
> 
> Is there a reason for this, what is a rule of thumb that could be used ?
> 
> Regards,
> 
> Peter Zak.
> 

From the archives:

I shoot IR film quite often in my M4, and it is quite easy. I don't usually
shoot wide open, but if necessary, I'll still do it. With newer lenses I
set the focus point approximately at the closer f/2 depth of field mark,
with older (70's) lenses I set it at about the f/4 mark. This is all with
the Kodak HIE film, which has sensitivity further into the IR than other
readily available films. With others (Konica 750, the E-6 film and the
Ilford film) I don't do any adjustment at all. Especially the more recent
lenses are so well corrected, and the IR sensitivity is so limited, that
refocussing rarely brings any benefits.

The shutter has no light leak problems.

For the Kodak HIE film I have a Leica 39mm IR filter, which is equivalent
to an 89B, and otherwise I use gels cut to size behind a UV filter; mostly
89B or 87. The 25 filter doesn't do quite enough with the HIE.

The main problem with IR is that you have to bracket a lot, and the film is
expensive, but if you are going to use it, Leica-M's are ideal.

   *            Henning J. Wulff
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