[pure-silver] Re: Calibrating a colour enlarger to ISO paper grades wrt Way Beyond Monochrome
- From: Claudio Bonavolta <claudio@xxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 27 Nov 2009 13:42:45 +0100
----- Message d'origine -----
De: Tom Kershaw <tom@xxxxxxxxxxxxxx>
Date: Thu, 26 Nov 2009 19:35:55 +0000
Sujet: [pure-silver] Calibrating a colour enlarger to ISO paper grades wrt Way
Beyond Monochrome
À: pure-silver@xxxxxxxxxxxxx
>I 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'.
>
>
>Tom
It'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
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