If there is no suitable photo frame it can be replaced by any opaque tape, stretched on the table of a photographic enlarger in the longitudinal and transverse directions. The ends of tape segments need to pull the rubber band. And DEBATIN, Engels

If there is no suitable photo frame it can be replaced by any opaque tape, stretched on the table of a photographic enlarger in the longitudinal and transverse directions. The ends of tape segments need to pull the rubber band.