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