So, it seems that the upshot of this is the same as it would be with "real world testing," where you print a step wedge for each filtration number and then read it on a reflection densitometer to find out what the scale of the paper is at each number?
Your method seems a lot more complicated. Why would you do it that way? --shannon On Nov 27, 2009, at 7:39 AM, Tom Kershaw wrote:
Claudio,I'm currently using dual filtration from the ILFORD Multigrade data sheet, not from real-world testing. Figure 1 of the 'Contrast Control with Color Enlargers' chapter in 'Way Beyond Monochrome' gives 'Test settings' to make eleven prints from a projection step wedge as follows:Test 1. Y 130, M 0 Test 2. Y 110, M 2 Test 3. Y 95, M 4 Test 4. Y 80, M 8 Test 5. Y 65, M 12 Test 6. Y 50, M 20 Test 7. Y 35, M 30 Test 8. Y 20, M 50 Test 9. Y 10, M 70 Test 10. Y 4, M 95 Test 11. Y 0, M 130The prints from the step wedge are then assessed with either a densitometer or a reflective step wedge, and graphed to provide the data on contrast and exposure performance. In the case of 'Way Beyond Monchrome' the end point in filtration terms is then given for the test paper (Kodak Polymax), e.g. 'ISO Grade 2' is given as Y 59, M 15. So the multiplication factor I applied is for the starting point of testing e.g. Y 65*1.54 = 100.1, M 12*1.54 = 18.48.Tom Claudio Bonavolta wrote:----- Message d'origine ----- De: Tom Kershaw <tom@xxxxxxxxxxxxxx> Date: Thu, 26 Nov 2009 19:35:55 +0000Sujet: [pure-silver] Calibrating a colour enlarger to ISO paper grades wrt Way Beyond MonochromeÀ: pure-silver@xxxxxxxxxxxxxI suspect this message may be best directed towards Ralph W. Lambrecht. Reading through the calibrating chapter in 'Way Beyond Monochrome' I noticed the suggested filtration values given for a Durst max. 130 unit enlarger are not symmetrical across yellow and magenta. i.e. the step progressions between each value are not numerically equivalent; is this correct, and how variable are these values relatively across different manufacturers of enlargers? For my DeVere 5108 model I applied a multiplication factor of 1.54, i.e. 130 becomes 200.2 units as the filtration values go upto '200'.TomIt's rare to have a symmetry or constant progression in the values of yellow and magenta with a color head when used for BW multigrade paper.Another example with my Focomat V35 (YMC filters go up to 200) with simple filtering:00 Y200 2.24 0 Y90 2.24 0.5 Y65 2 1 Y50 1.78 1.5 Y25 1.41 2 ---- 1 2.5 M20 1.41 3 M40 1.78 3.5 M65 2.24 4 M100 2.82 4.5 M140 3.16 5 M200 3.16 Column 1: grade with Ilford Multigrade IV Fiber Column 2: filtration Column 3: exposure compensation (ref. density of 0.60)Here too, you can see there is no symmetry and no linear progression either.The factor you applied based on Ralph's own enlarger values may or may not be correct. If you want a progressive scale of contrasts, you've better to test it with a step wedge. Keep in mind these filters values are not really standardized, there are some big groups where results are similar, but, for precise work, you must fine-tune your enlarger. And because filters may fade with time you have to re-do it from time to time.Note also that you may have simple filtering, i.e. using a single filter at a time but this requires time compensation, or double-filtering, i.e. using a mix of yellow and magenta as to keep constant exposure, or split-grade filtering, i.e. 2 different exposures done with either full magenta or full yellow.Claudio Bonavolta http://www.bonavolta.ch====================================================================== ====================================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.
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