[Leica] IR filters

[henningw at archiphoto.com (Henning Wulff)]

At 2:53 PM -0600 2/3/07, Lottermoser George wrote:
>Could some of you IR photographers please comment on comparison of:
>
>Dark Red 092 (89B)
>The nearly opaque B&W 46 mm Dark Red Infrared (092 = 89B) Filter, 
>which looks dark purplish-red when held in front of a light source, 
>blocks visible light up to 650 nm, and passes only 50% of the 
>radiation just below 700 nm (thus the dark red color). From 730 nm 
>to 2000 nm, transmission is greater than 90%; This makes photographs 
>of pure red and infrared images possible with the best utilization 
>of the relatively low sensitivity of infrared films As the 
>sensitization of infrared black and white films barely extends 
>beyond 1000 nm, the red portion that is transmitted still makes a 
>relevant contribution to the exposure; That is why this filter is 
>the preferred filter for pictorial photography on IR black and white 
>film.
>
>and
>
>093 (87C)
>Removes complete visible spectrum. This B&W 46 mm 093 (87C) Infrared 
>Glass Filter blocks the entire visible spectrum, so to our eyes it 
>looks completely opaque. Unlike the B&W 092 infrared filter, it 
>makes pure infrared photographs possible without the visible red 
>component. Its transmission only begins to exceed 1% at 800 nm, 
>rising to 88% at 900 nm, and remains that high far beyond the upper 
>limit of sensitization covered by infrared films. This filter is 
>used less frequently in pictorial photography because of the 
>dramatic loss of effective ISO. In the scientific field, materials 
>research and forensics, the limitation to a strictly infrared range 
>is often important.
>
>How do these descriptions translate into real world use (exposure, 
>focus compensation, etc.) and relative "look" of IR images?
>
>TIA for helping me learn about this field.
>
>Regards,
>George Lottermoser
>george@imagist.com

The 092 is pretty much equivalent to the Wratten 89b, and the 093 to 
the Wratten 87. The 092 will give you IR effects, but also a bit of 
visible light will come through. Focus adjustments are slightly less 
with the 092 compared with the 093, but you have to experiment with 
this. It depends on which lens you use. Even slight variations in the 
lens formulas can affect the IR focus shift quite seriously.

With the M8 the difference in exposure seems to be on the order of 1 
stop to 3 stops, depending on conditions. The main difference that I 
noticed is that the M8 metering seemed to work just fine through the 
092, but was not as reliable through the 093. The meter is not as 
sensitive as the sensor at the longer wavelengths.

The difference in look is not really huge, for the most part but 
again depends a lot on the subject and lighting.

I would suggest starting out with the B+W 092 or equivalent out of 
these two. You could then try a 093 if you get into it more.

Or, if you are ordering Heliopan filters anyway, order a #5715 which 
is an 88A equivalent, which cuts out more of the visible than the 89B 
and lets in more shorter wavelegths than the 87. This would be the 
ideal filter for most IR photography, as it allows shorter exposures 
than the 87 but still allows a stronger IR effect in most ways 
equivalent to the 87.

If you order it through the people I suggested before, a 39 to 49mm 
size would cost about $50.00.

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    *            Henning J. Wulff
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