[pure-silver] Re: Ralph Lambrecht / EM10 enlarging meter?
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 7 Jan 2005 10:31:50 -0800
----- Original Message -----
From: "DarkroomMagic" <info@xxxxxxxxxxxxxxxx>
To: "PureSilverNew" <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, January 07, 2005 8:48 AM
Subject: [pure-silver] Re: Ralph Lambrecht / EM10 enlarging
meter?
>I still would like to understand what these numbers mean.
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> Regards
>
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> Ralph W. Lambrecht
>
>
The dial setting is only a starting point for calibrating
the meter by making test prints. From the minimal literature
supplied with the meter is is set to give nominal 30 second
exposures for Ciba/Ilfochrome from some sort of standard
negative. Presumably the dials are set at the factory using
a standardized light source. In actual use the dial is
calibrated by the user for a convenient exposure time for
the range of stops where the enlarging lens performs well.
In order to be able to use the meter for different times or
different ranges of light level, such as making very large
prints, it is necessary to re-calibrate the dial by making
test prints.
I've found it useful to measure the dial numbers
corresponding to one stop changes in light level. I record
these on a sheet kept in the box and on a bit of tape on the
back of the meter. One can also mark the dial with a marking
pen. If you do your own calibration the reference value can
be ignored.
Ilford recommends that the meter be used in a fairly
bright area of the projected image. For a negative it should
measure a shadow area that is to have detail, for a
transparency a highlight area that is to have detail. While
the meter is sensitive enough to give readings in denser
parts of the image it is not really intended to be used as a
densitometer. For the range of densities found in normal B&W
negatives the highlight density is likely to be difficult to
read. The advantage of making measurements on the enlarger
baseboard is that any Callier effect is automatically
compensated for. Callier effect is the variation in apparent
density with type of illumination due to scattering by the
silver particals in the emulsion. It is greatest for coarse
grain and thick emulsions, least for fine grain, and nearly
non-existent for the dye images of color film. The practical
effect is to increase apparent contrast when silver
negatives are printed using a partially specular source,
such as a condenser enlarger, compared to a diffusion
source. Most densitometers measure diffusion density. In
average B&W film the difference is around one paper grade so
it is significant.
No simple meter will exactly predict the required
exposure and contrast grade needed by a negative. I suspect
that a scanner could be used with appropriate sofware to
completely chacterize film originals, both negative and
positive, for both of these plus filtering required for
color.
In any case, I find the EM-10 very useful. It does not
eliminate tests and having to make visual judgements but
does reduce the amount of exposure testing considerably.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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