[Leica] Some IR filtration experiments

[henningw at archiphoto.com (Henning Wulff)]

At 4:25 PM -0500 11/15/06, Leonard Taupier wrote:
>Mark,
>
>Great work. Your results are especially interesting to me as I want 
>the kind of sensitivity to IR that the M8 has. I shoot a lot of IR 
>photos. That's just the opposite of everybody else. I'm very 
>familiar with the IR sensitivity of the D200 (none), the D2H (little 
>more than average), D2X (a little less than the D2H), and D1X ( more 
>sensitive than the D2H). The hot mirror IR filter approach may be 
>fine in the short term but that's slowing down all your lenses by 1 
>to 2 stops. Since your experiment with the Phase One profile has 
>only limited success, you're right. Leica will have to fix it. That 
>may not be too easy as Leica has already suggested that adding an IR 
>filter over the sensor may (my interpretation) mess up their edge 
>performance they went so hard to develop). Your new Heliopan filter 
>experiment will be interesting but I think the UV contribution to 
>the problem is very minor compared to IR. Most modern lenses roll 
>off UV fairly well.  I have to use enlarging lenses for UV images. 
>And your D200 also has absolutely no sensitivity to UV. It looks 
>like a winner right now. While I want the IR sensitivity of the M8, 
>not at the expense of color cast problems. For now I'll just wait 
>and see how the M8 evolves and continue to buy more film for my M6 
>and M7s.
>
>Thanks and keep us informed on your future experiments.
>Len

Len, my interests are also definitely more in the IR usability, and 
less in colour accuracy. But the hot filter solution is definitely 
the correct one, whether as part of the filter pack or front-of-lens. 
Coatings and therefore flare are issues with lens filters, so the 
more elegant, though one-sided solution is to add the filtration to 
the filter pack in front of the sensor.

Hopefully the B&W Digital M, should it materialize, will keep the 
full IR sensitivity.

-- 
    *            Henning J. Wulff
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