Archived posting to the Leica Users Group, 1997/10/07
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]At 06:36 PM 10/7/97 +0100, you wrote: >>>Gene Nocon--a gentleman who runs lab across the street from studio and >>>has printed for many greats uses a blue filter in his focusing tool = =20 >>>Without it he says prints arent truly focused He showed me print >>>coparisons and he is right Probably big factor at wider F stops =20 >>>Apparently this is standard knowleddge among high level lab types When >>>I get back into do my own printing I will definitely get the >>>filter maybe APO lenses dont need it I`ll ask when I return >>>Donal Philby > >I've just got the book by Gene Nocon "Photographic printing" and in it he says; > >"Using the blue filter on the Omega Micro-grain focuser; at this= enlargement >the grain can be seen to be pin sharp on the print. The image projected= onto >the easel will actually appear out of focus after focusing with the blue >filter, but the print will be sharply focused. >Without the blue filter on the grain focuser the image appeared to be in >focus. The resulting print, however, is out of focus." > >This suggests to me that it is not a question of using a blue filter to >increase contrast or reduce brightness, but that the image that appears on >the paper when printed is formed from predominantly blue light or light= that >is focusing in the same plane as blue light. Otherwise, the image in the >above description that was focused without the blue filter would be in= focus >when developed!=20 > >What is not clear is how this applies to VC paper. The answer, or some of >it, may be in Ctein's Darkroom User article (Darkrrom User, 1996, #1) on= the >best enlarging lenses, where he says; > - ------------------------------------------------------------------- >Hi Jim, I=B4ve been thinking about the blue filter in grain focusers, dont >you think that the reason may lie in that the really actinic ligth is >the blue component of not so white ligth prodycec by the enlarger?, we >may be focusing wiith the ligth that really matters as far as paper is >concerned., What do you think? - --------------------------------------------------------------------- YOU ARE ALL PROBABLY CORRECT. The #90 that I use really isn't "blue", but it works for me, perhaps by improving contrast and cutting the bright enlarger light at f/2.8. I print on Ilfochrome paper so I need all wavelengths to be in focus. I use an APO lens, which, hopefully, can focus all wavelengths at the same point. But my grain focusser neither has an APO eyepiece nor an APO mirror! I have no scientific proof that any of this makes any difference, just experience. My prints are sharp. Go figure... Jim