This thread is becoming very interesting - lots of tricks!
So there goes another one:
I have a very simple enlarger - Opemus III, no filterhead, etc.
Using VC filters is not a problem - they can be placed between condenser and neg carrier - but no ND filter...
Yesterday I've just installed a standard light dimmer inside my EPOI enlarging timer (sure, one can use an external unit - but this way is neater) so the elarger lamp can be fine tuned to the light I need.
I have an Opemus 6a with colour head, which includes an ND filter along with the common C/M/Y. Great for fine-tuning exposures. But only up to 6x6...
I also have a Durst 138S with condensor head. I use this with grased paper, or hand-held Cokin filters under the lens (!). This seems to give an adequate range with most VC papers. I have test-printed the paper/filter combinations with the step-tablet in the negative carrier; without, with yellow, and with magenta filter. All at the same time and aperture. That way I know exactly how the filters influence the exposure. Exposing to desired contrast grade is done by simple (mental) arithmetic... It's a kind of split-grading, except that I use unfiltered and either yellow or magenta filtration. So far, it seems to work - to my considerable surprise!
-- Ole Tjugen, Luddite Elitist
Yup, dimmers will change the color temperature of the light and result in having to fine tune your filtration for every setting of the dimmer as the blue component of the light fades. An ND filter is really the best way to get rid of too much light. ND filters should be fairly easy to find.
Originally Posted by Jorge Oliveira
I see your point.
However, I've decided to give it a try since:
- I have no other way to fine tune light output at this time (I don't have a Vc head).
- Adjustments will be minor - say +/- 0.5 f stops.
- If you take the spectrum of an incandescent lamp and of a cold light source, they are quite different, but there are no different VC filters for each of these light sources, so maybe that's not a major issue.
Next time I do prints I will let you know.
Good, Jorge! I wouldn't ever say you can't make it work, but the variables will make life interesting. I'd mark the positions of the dimmer, or better yet put a volt meter on the line and work at "standardised" voltage levels so you will know what point you are working from. As the voltage drops the bulb output will redden fairly fast. Let us know how this progresses.
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A cold light does need a yellow filter of a some value I can't remember added to it to get in the proper range for VC filtration. Otherwise you have to calibrate and disregard the numbers on the VC filter and figure out the grade you are getting by comparing the results to graded paper.
Originally Posted by Jorge Oliveira
Ok, I'm really not familiar with enlarger's cold lights - that was my guess.
I do know that standard fluorescent lights 'daylight type' 6400K (AKA cold light) have two main lines in the green (strongest) and blue wavelenghts, so it would make VC paper soft...
I thought enlarger's ones were a somewhat special.
Now, some practical data:
I've just made two small enlargements of the face of the Sculptor (see gallery).
One was firstname.lastname@example.org; the other one ended at 10.5s@f4 - so, a bit over 1 f stop light reduction using the dimmer.
My reference was the white mark at his forehead, filter grade 3, Polymax II paper.
Yes, there is a diference if you put them side by side - but I would say less than 0.5 grades.
So, I believe that for 0.5 f stops (my intended usage, 1 f stop I get from the lens), it will be insignificant.
Thanks for your comments,