Pellicles are essentially single surfaced beamsplitters. In this case one face carries the partially reflecting film and the second, uncoated, surface will produce a roughly 4% ghost image. But the ghost image will be displaced only ~2 microns laterally from the primary image and may usually be ignored.
Mirrors
Hot Mirrors and Cold Mirrors
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Prisms
Optical Prism Selection Guide
Nov. 1, 2024