Re: [Leica] Noctilux and filters

["Mike Durling" <durling@widomaker.com>]

Joe:

Infrared light focuses at a different plane than visible light.  There is an
"R" on many lenses that marks the approximate infrared focus point.  You
focus as normal and then you are supposed to move the distance on the scale
from the arrow to the "R".  I don't know if the Noctilux has this.  I assume
this is for B&W infrared with the black filter.  Since most people shoot the
IR Ektachrome with a yellow or green filter a lot of visible light mixes in
with the infrared.  Still the focus shift may explain the out of focus shots
at F-1

Mike D

- -----Original Message-----
From: Joe B. <joe-b@dircon.co.uk>
To: leica-users@mejac.palo-alto.ca.us <leica-users@mejac.palo-alto.ca.us>
Date: Saturday, January 22, 2000 11:09 PM
Subject: [Leica] Noctilux and filters


>What I am curious about is exactly why Leica recommend (I can't remember
>exactly where I read this) that filters not be used with the Noctilux. They
>don't say this about most of the other Leica lenses, and I wonder what the
>distinction is. I have used filters with the Noctilux in situations where
>it was the only thing to do, like for example with Infrared Ektachrome. I
>didn't get many correctly focused shots that time, and I wonder if possibly
>the filter affects the focus accuracy with such a wide aperture lens. On an
>SLR with TTL focusing I don't think it wouldn't be an issue, but with a
>rangefinder it might be. I wonder if anyone who knows about filters and
>focusing errors could comment on this.
>
>Joe B.
>
>