[Leica] geebee Ilford SFX processing

[henningw at archiphoto.com (Henning Wulff)]

At 7:21 AM +0100 5/18/07, geebee wrote:
>From: "John Biava" <leicam4pro@yahoo.com>
>To: "Leica Users Group" <lug@leica-users.org>
>Sent: Friday, May 18, 2007 12:53 AM
>Subject: Re: [Leica] geebee Ilford SFX processing
>
>>
>>  The exact characteristics of the filter you are using also make a 
>>big difference.  A R 25 is not really an IR filter, but seems to be 
>>about all that is readily available now.
>>
>------------------------------------------------------------------------------------------------
>John,
>
>I have a Leitz IR filter in 48mm for my 90 cron which I had 
>completely forgotten until I read your post so  I may have to 
>revisit SFX. I think also that SFX just has heightened sensitivity 
>to red but isn't a true IR film.
>
>--Graham

The Leica IR filter is similar in transmission characteristics to the 
Wratten 89B, B+W 092, Hoya R72 or Heliopan RG-695. With all you can 
see the light source through the filter if you hold it up toward it 
(don't do it with the sun!!). This filter is intended to come as 
close as possible to dividing the visible from the infrared.

Heliopan has a series that includes the RG-645 (like the B+W 091, a 
dark red) through the RG-665,695,715,780 and 830. The 830 is like the 
Wratten 87 or B+W 093; ie, quite dense.

SFX works with the 89B or Leica IR filters, but has a fairly hefty 
speed penalty with that; I forget what as I haven't used that film 
but once and didn't bother again.

With the M8 you can use all the filters. In fact, with all of them 
you can just meter as normal and shoot. In fact, the meter is so IR 
sensitive you usually have to dial back a bit in the compensation 
about 1 stop so that you don't clip the red channel, which is where 
all the information is.

-- 
    *            Henning J. Wulff
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