[pure-silver] Re: Ralph Lambrecht / EM10 enlarging meter?
- From: "Ole Tjugen" <oftjugen@xxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 07 Jan 2005 19:56:32 +0100
In my case, a reading of 80 corresponds to a a zone VII to VIII highlight
on Ilford MG IV at 10 seconds exposure. Shadows (zone II 1/2 equivalent)
vary from 20 to 50 depending on filtration, but highlights stay constant.
That saves me a LOT of test strips!
Ole Tjugen
<snip>
> 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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