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There are dozens of others. This system is used only for monochromefilters, not for color correction filters. ---Richard KnoppowLos Angeles, Ca.dick...@ix.netcom.com

K2 and X1 are Kodak (Wratten) type indicators. These letter andnumber combinations date back to the first filters and have littlerational basis. Other filter manufacturers used other letter andnumber designators (although some adopted the Wratten system), like Y2for K2, lists can be found in many old handbooks. Some filter makerssimply named the filters, i.e. Medium Yellow. The number only system became a standard about the mid seventiessometime. Other systems continued to co-exist for many years. Thenewer system is consistant amoung manufacturers so a #11 is the samething regardless of who makes it. That is not to say the quality orexact spectral transmission will be the same but it will be a mediumGreen filter and not something completely different. There have been a tremendous number of filters offered commerciallyover the years including a great many special purpose filters and somepretty close duplications. Many of these have disappeared due tolittle volume or the use of un-stable colorants. The most commonly used filters for B&W are:Old Wratten No. New type no. ColorK1 #6 Light YellowK2 #8 Medium YellowK3 #9 Dark YellowX1 #11 Light GreenX2 #13 Medium GreenG #15 Deep Yellow or Light OrangeA #25A Medium RedC5 #47 Blue There are dozens of others. This system is used only for monochromefilters, not for color correction filters. ---Richard KnoppowLos Angeles, Ca.dick...@ix.netcom.com

The 47 blue and 61 green are used to make contrast changes in variable ormulti contrast paper used below an enlarger light source.SSMichael Gudzinowicz wrote in message<77gdsk$b...@freenet-news.carleton.ca>...