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 [attachment 119532 CrossPol15.jpg][attachment 119533 Camera_with_lights.jpg] Any advice appreciated. Mike https://reprap.org/forum/read.php?138,889665,889665#msg-889665 Tue, 15 Sep 2026 20:18:32 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?138,889665,889665#msg-889665 Questions on photogrammetry using cross-polarization:- https://reprap.org/forum/read.php?138,889665,889665#msg-889665
  • 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
    [attachment 119532 CrossPol15.jpg][attachment 119533 Camera_with_lights.jpg]

    Any advice appreciated.

    Mike]]>     leadinglights 3D Scanners, Book Scanners, and Optics Mon, 13 Jun 2022 06:05:10 -0400