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Having the Photographic Masks Made

The slit masks used by the COSMIC spectrograph are made by reproducing photographically at a reduction factor of 4 the output of the COSMIC slit mask assignment program. Thus the slits correspond to places where the film is clear (but there is still some transmission loss of course), and the remaining area must be very opaque. If the contrast in transmission between the slit and the dark area is not at least 104, then sky light may well leak in and contaminate the exposure at a noticable level. Thus the two critical concerns for the photographic lab are the exact reduction by a factor of 4 of the supplied image and making the mask area (except for the slits) as opaque as possible.

The printed mask should be taken to:
Commercial Graphics
681 South Raymond Ave.
Pasadena, CA 91105
(626)583-1122

Note that the actual negatives are shot in their LA office, but materials may be dropped off and picked up in Pasadena. Tell them you would like a 4x reduction of each mask, on extremely opaque negatives, with reverse reading. Make sure to tell them you will actually want the negative itself. Four masks can be placed on a single sheet of negative, for a cost of about ten dollars per sheet. It is good practice to have two copies of each mask made, as small defects are not uncommon.



Roy Gal
2/11/1999