Questions on photogrammetry using cross-polarization:-

• Is an extinction ratio of 0.9 to 0.95 good enough for cross-polarization photogrammetry? (this number is an educated guess)
• Do circular polarizing photographic filters have a worse extinction ratio than linear polarizing filters?

Further information:-
Early 3D scanner rigs that I have built have been somewhat disappointing so I am in the process of building another rig. This one consists of a turntable from a Ciclop scanner, a Raspberry Pi high-quality (10MPx) camera with a 16mm lens, and a polarizing filter. Two MR11 spotlights with polarizing filters are used for illumination: these are 37mm circular polarizing filters with the 1/4 wave layer towards the light source.

The problem I have is that looking directly through both filters and adjusting for maximum extinction is a bit like looking through dark glasses - not at all like the near total extinction I expected. Looking at the view from the camera and adjusting both spotlight polarizers and camera polarization reduces the specular highlights but not to the point of extinction.

Edit: Attached photo showing highlights reduced but not extinguished, also a picture of the camera with polarized spotlights


Any advice appreciated.

Mike

Edited 2 time(s). Last edit at 06/13/2022 08:12AM by leadinglights.