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Contact Sheet/Callier Effect?
Len wrote (in part):
It is often stated that if you want your prints to have similar tonal values to your contact prints you need to try diffusion or cold light as your illumination source. I use a condenser enlarger and I have noticed a change in values from the contact sheet to the print even before I was aware of the different light sources and the Callier effect . I have always just attributed the difference to the visual effects of scale-up. Medium format to 8x10 or 11x14 . I do know this though: I have never been fully happy with my tonal values, especially the highlights. In fact between this and the very noticale dry-down effects of Illford fiber based paper it drives me nuts. In making my contact sheets I place the negatives on the paper under a sheet of glass. In the enlarger I have the 2 1/4 in film holder. I focus the light so that the edges of the (empty) film holder are sharp at he easel. So, the enlarger is focused and at a height very much as it would be if I was making a print. Back to my question. Since this is a condenser enlarger is this light still collimated or not when it strikes the paper after traveling throug the lens? Is the Callier effect at work when I make a contact sheets or not? Please explain. Actually, it does not make any difference if the light is collimated when you are making contact prints. Where it matters is when the distance between the emulsion and the enlarging lens is large, such as between the negative and enlarging lens in a typical enlarger in normal use. This is because the collimated light is scattered by the grains in the negative, and the scattered light pretty much does not make it to the lens. Where scattering might make a difference when making contact prints is when the distance between the emulsion in the film is distant from the printing paper. The typical contact printing arrangement is such that this distance is extremely small. So even if you used a point source of light through perfectly focused condenser lenses onto the entry pupil of the enlarging lens at one extreme, and a cold light diffusion source at the other, you would see no change (other than exposure difference if they sources had different useful intensity). The difference would be noticed in the enlarging situations, as Richard has already pointed out. Now I have used both semi-collimate light from a normal enlarging bulb through Beseler condenser lenses, and also Aristo and Zone VI cold light heads and prefer cold light heads (for B&W). But satisfactory prints can be obtained with either. If you calibrate your exposure system and negative development, you will get the same results. Richard says so. Dr. Richard J. Henry, who really ought to know, and I say so. The claims of preference of one type vs another seem mostly from people who have not really calibrated their exposure and development to give the same print contrast. The main advantage to cold light enlargement is that the negatives have less of a chance to pop from the heat. Since I use a Beseler neg-a-stretch holder, they do not pop, although some people call that holder a neg-a-scratch holder. I never compose that close to the edge, so it does not matter to me. Another claim, that I do not find matters to me; i.e., I cannot duplicate it, is that dust is less visible from prints using diffused light. I do not see the improvement. I can see dust no matter what kind of light I use. And since I am a hopeless print spotter, all I can do is toss the print, clean the negative again, and make a new print. I have a Zone VI high voltage electrozapper brush that works very well on 4"x5" negatives. Not quite so well on 35mm ones (brush is too big). I got one long ago. The last time I saw the price for one, I thought it was too high. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 22:35:01 up 27 days, 1:53, 3 users, load average: 4.98, 4.77, 4.76 |
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