[rollei_list] Re: [rollei_list] Re: OT: Voigtländer Avus
----- Original Message ----- From: "Marc James Small" <marcsmall@xxxxxxxxxxx> 
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Monday, June 16, 2008 8:27 AM
Subject: [rollei_list] Re: OT: Voigtländer Avus



On 6/18/2009 10:35 AM, J Patric Dahlén wrote:
Pan- and orthopan films must be handled in complete darkness, but ortho films (like Efke 25 ORT or Ilford Ortho Plus) can be handled in 
dark red light.
Well, no. A dim green safelight will work well with pan films -- back in the dieing days of darkrooms, some folks were selling LED lights in that range. Ortho films can tolerate a brighter reddish light. Hollywood still portrays photographers, even digital dudes, mucking 
about in an orange-lit darkroom.  Go figure!

Marc
See Kodak's instructions for pan films. The reason that a green light is used is two fold: The dark adapted eye is most sensitive to green and many, especially older, pan films have a dip in sensitivity around green. Kodak recommends the following: "A Kodak Safelight Filter, Wratten Series 3 (dark green) in a suitable safelight lamp with a 15 Watt bulb can be used for a few seconds _only_, at 4 feet, after development is half completed." The partial development desensitizes the film to some degree. Dark red safelights are reasonably safe for orthochromatic materials. The term "orthopanchromatic" is somewhat obscure but I think it was used for ortho materials with extended green sensitivity, a dark red safelight is probably safe for them but the individual data sheets should be consulted. Some modern printing papers of the variable contrast type have enough sensitivity in the green region to require a red safelight although the usual amber Kodak OC lamp will work with most. The OC has higher visual brightness than a red lamp of the same measured brightness so it may have an advantage for certain materials. Its also more pleasant to work under. Non color sensitized materials can be worked with under amber or red lights but some slow materials can also be safe with a yellow light. I feel the same way Marc does about the way photographic darkrooms are shown in the movies. My other bugaboo, being an inveterate reader of detective stories, is the number which assume that photographers have an unlimited supply of cyanide in their darkrooms all ready to poison people with. While there are cyanide compounds, like potassium ferrocyanide, used as bleach its not a very good poison and true cyanide is very rarely used in general photography. Newspaper plants did have it, for making half-tone plates by the old method which is essentially the wet plate process. Cyanide is a component of Monckhoevn's Intensifier, which also contains mecuric chloride, another rather nasty poison. This solution was used to clean up dots since it has the peculiar property of being an intensifier for dense parts of the image but a reducer for low density parts. The old method of half-toning has not been in general use since perhaps the 1940s. 

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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