On Monday 19 September 2005 04:02, Peter Badcock wrote: > OK. So I just did a bit of reading about how contrast is controlled on VC > papers, and it is set by the ratio of blue:green light. Magenta filter is > red+blue (no green). Since the paper is insensitive to red, the blue light > component in magenta is all that is seen by the paper. The only way I could > see that a #47b blue filter would offer any increase in contrast is if it's > ration of blue:green is > than the ratio of blue:green in the magenta > filter. These wratten curves > (http://www.geocities.com/thombell/curves.html) don't give an answer since > neither #33 nor #47b show any green component. I'd rather not buy a blue > filter if the effect will be marginal or un-noticeable. Maybe Ilford's #5 > is not the same as wratten#33. The 47b is nothing but blue. The green version [58?] is nothing but green. I doubt the Ilford #5 is pure magenta. It's intended to provide a #5 grade on Ilford paper. That's the only thing it's trying to do. You could do a grade test with your #5 filter but I guess that requires a step wedge. I know with the colour head on my Durst I can't hit grade #5 with the built in filters and Agfa paper. Instead of buying the 47b and the 58 you could buy some Roscolux lighting filters. Much cheaper. Work well above the negative. I don't remember the exact numbers but you can check the website and see the curves. Nick ============================================================================================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.