Date: 09/25/01-10:54:40 AM Z
<< Many texts on making unsharp masks suggest placing a thin sheet of
glass or sheet of clear mylar between the original
negative/transparency and the film being exposed. You do not do this? >>
They all achieve the same purpose of blurring the mask one way or another. In
the description given (in the original email), the white acrylic diffuses the
light source so that it is no longer collimated. The light shines in all
direction. The original is oriented face up (emulsion touching the glass),
which means there is a distance (which is the thickness of the base) between
the original image and the emulsion for the mask. The net effect is the
diffused light going through the image, then some distance (though very
small) before reaching the emulsion, thus blurring the mask.
In the texts that you mentioned, the blurring is achieved by placing a
diffusion sheet between the original and the film for the mask.
If you are using sheet film that doesn't have anti-halation layer, you might
have read another method of sandwiching the original and the film for the
mask back to back (instead of the usual emulsion to emulsion in normal
contact printing), so there is again distance between the emulsions, so
blurring is achieved.
I forgot it was Phil Davis or Ctein who also wrote an article on masking. He
uses a contact frame, put the film for the mask under the glass but the
original negative above the glass! Enlarger is used as the light source. The
light is collimated but the distance between the original and the receiving
film is so big that the mask is certainly blurred.
So the main thing is to achive the blur. Most people would say that the
amount of blur is not critical. That is to a certain degree true, but how
blur it is of course determines how much sharpening effect you want (in
Photoshop term, this amount of blur would be the radius for the unsharp mask).
<< When using the unsharp mask in making exposures what is the
orientation of the negative and mask?
The emulsion of the original negative should face the emulsion of the
receiving film to ensure maximum sharpness. The mask is above the original
negative. The mask is less critical because it is blur anyway.
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