If the GEPE mounts are used, does the slide have to be removed from the mount to be scanned or printed?
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Not necessarily but if left in the mount it adds another optical interface and likely further degradation of the scanned image. Removal from the mounts can increase the potential for damage to the film and at least for home scanning, dealing with a single frame is a PITA. My suggestion for cost effective use of 120 film in 2011 is to home/commercial lab develop B&W, commercial lab develop color and home scan with an Epson flat bed. The small number of exceptional images should be sent out for high quality (expensive) drum scan. If cost isn't a consideration then get a Hasselblad/Imacon X5 scanner.
Steve