[Leica] IR filters

[abridge at gmail.com (Adam Bridge)]

I am sure hoping someone who is practicing IR photography can respond?
I'd also find the answer valuable.

Adam

On 2/3/07, Lottermoser George <imagist3@mac.com> 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
>
>
>
>
>
>
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