The PC filters made by the paper manufacturers are designed to allow contrast changes while at the same time keep exposure changes minimal as you move from filter to filter. If you want the highest contrast possible from a paper just expose with a blue filter. Any blue filter. If you want to be precise get the spectral sensitivity curves from the paper manufacturer and the dye density curves for the filter and see where the filter cuts off and the valley for the high contrast dip is and blend the two. You are not interested in ratios. You want to cut (clip) the exposure to the soft contrast silver grains. With out looking, 500nm should be a good valley location so a 47B will work well. The difference between Blue filters and magenta filters is additive vs. subtractive systems. Dave ----- Original Message ----- From: "Nick Zentena" <zentena@xxxxxxxxxxxx> To: <pure-silver@xxxxxxxxxxxxx> Sent: Monday, September 19, 2005 7:15 AM Subject: [pure-silver] Re: How do I increase local contrast in my shadows when printing? > 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. ============================================================================================================= 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.