Archived posting to the Leica Users Group, 2003/12/07

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Subject: Re: [Leica] IR Infrared Filter
From: Henning Wulff <henningw@archiphoto.com>
Date: Sun, 7 Dec 2003 16:59:03 -0800
References: <26C37BB4-290F-11D8-A88E-000A9578C446@ncable.net.au> <075501c3bd20$6a4696c0$0200a8c0@Desk>

At 6:15 PM -0600 12/7/03, robertmeier@usjet.net wrote:
>Does anyone know if Leica ever made an infrared filter like the one Rollei
>made?   The Rollei filter is distinguished for two things:  it is all but
>opague, only passing the infrared wavelengths, and it is slightly ground to
>compensate for the different focus point needed for infrared light, so no
>compensation is needed on the focus setting.   Since with a Rollei, like a
>Leica, you don't view through the taking lens (and the filter), the opague
>filter works all right.  I would love to use such a filter on my Summircon
>50, and I might have to tape my Rollei Bayonet II filter on to it (the
>diameters are just about identical).

Leica made IR filters, generally equivalent to Wratten 89B, but with 
no optical adjustment such as the one for the Rollei. The latter 
works even less well for the Leica than the Rollei.

A focus adjustment is lens dependent, filter dependent and film 
dependent. If the Rollei filter is made for a specific lens, it's 
important to find out what film it's made for. Most likely HIE, but 
not necessarily. Again, note that this only works for a specific lens 
formula. The possible variations is the reason that Leica no longer 
puts an IR correction mark on the focussing mount of lenses. You 
gotta find it for yourself, for your parameters.

With Leicas, the fact that the filter could be used on a variety of 
different lenses means that no specific optical adjustment should be 
made in the filter, but that tests should be made with the specific 
lens/film combo for each filter.

On a related note, last weekend my son and I were playing with his 
Panasonic LikaLeica, and discovered that it had significant 
sensitivity even with an 87C filter. An 87 seemed the best match for 
the camera, or possibly an 88A (which we didn't try). Reasonable 
exposure times, and a very clear IR effect. The strange thing was 
that if you used an 89B, the picture came out red, but if you used an 
87C, it came out B&W. There must be firmware in there that switches 
to B&W past a specific spectral response; it means that the Panasonic 
engineers were planning for this camera to be useable in the IR.

- -- 
    *            Henning J. Wulff
   /|\      Wulff Photography & Design
  /###\   mailto:henningw@archiphoto.com
  |[ ]|     http://www.archiphoto.com
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Replies: Reply from robertmeier@usjet.net (Re: [Leica] IR Infrared Filter)
In reply to: Message from Alastair Firkin <firkin@ncable.net.au> (Re: [Leica] PAW 49 dlridings)
Message from robertmeier@usjet.net (Re: [Leica] IR Infrared Filter)