When viewing the focal plane with a film emulsion mounted in the film holder, the face of the film may be featureless except for a few random dust specs. | To add some depth to the bland film emulsion to aid focusing, lightly dust the film plane with fine talcum powder. Be sure to thoroughly clean the powder off the film holder before doing photography. |
Scratching a mark into the film with a fine pin point shows as deep gouge with the high manification of the focusing scope. | Numbering the edge of the film plane where each Invar rod is adjusted allows recording the effect of each focus adjustment. |
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