[pure-silver] Re: New color head "discoveries"
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Thu, 13 Jan 2005 14:01:42 -0800
----- Original Message -----
From: "Rob Champagne" <app@xxxxxxxxxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, January 13, 2005 9:56 AM
Subject: [pure-silver] Re: New color head "discoveries"
> big snip
>
>> The filters of a color head will not give you the full
>>range of contrast available from VC paper with the use of
>>dedicated filters. They should give you a couple contrast
>>grades on either side of "normal" but filters should be
>>used
>>to obtain the maximum and minimum contrast values.
>
> big snip
>
>>---
>>Richard Knoppow
>
> I wonder whether my observation is true for other dichroic
> filter head enlargers.
> The Ilford Y+M figures for grade 2 on my Durst CLS501 head
> enlarger give approx an ISO grade 1 result on paper.
> It occurs to me that because dichroic filtration does not
> seem to give as much contrast as filter sets, and because
> most new enlargers have dichroic heads, that Ilford, and
> maybe other manufacturers, use this to its advantage in
> terms of film speed.
> To get a true ISO grade 2 using ilfords G2 Y+M figures for
> my enlarger I have to give the negative more development
> which in turn gives allows a faster film speed.
> So what I'm speculating here is that modern film speeds
> may be tailored by the manufacturers to suit printing on
> dichroic heads with Y+M filtration.
> It should be noted that by using increased development of
> the negative the overall contrast obtainable from a
> dichroic is not far short of a true G5 and if you take neg
> development far enough then a true G5 is obtainable from a
> dichroic head.
>
> It all depends on what you are tailoring your development
> to. Do it to 0 filtration and your negs will be too soft
> for G5 on dichroic settings. Do it to G2 Y+M settings of
> your dichroic head and you will get faster film speed and
> availability of higher contrast in your print.
>
What are the other conditions of the comparison? Are the
filters being used in the same enlarger or a different
enlarger? What I am trying to get at is that if the filters
are being used in a condenser enlarger the difference in
contrast will be due to that. Color heads are very diffuse
sources. The type of light makes little or no difference to
the dye images of color but will change the silver image
film about one paper grade.
If the settings of the color head re right for the paper
it should exactly duplicate the contrast of a filter for
that grade. The limitation of the color head is that it may
not be able to reach the extremes of the contrast range of
the paper. This is normally of little consequence.
Since ISO film speed is measured at a fixed contrast
(about right for diffusion printing) a change in contrast
will result in a change of effective speed. changing the
contrast up or down about one paper grade will result in a
change in film speed of around 3/4 stop up or down. Changing
either film conrast or paper contrast should have exactly
the same effect on the print.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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