Spiratone and Spiratone Colorflow™ Polarizing Filters

Discussion in 'Classic Manual Cameras' started by jdm_von_weinberg, Feb 18, 2013.

  1. Somehow in another thread the question of linear polarizers and modern cameras appeared, and I wrote in that one. It seems that I already wrote here, but that was years ago. First, I remember Spiratone back to about 1968, when I had a subscription to Pop. Photo when I was about 10, though I couldn't afford the things in the ad. My dad did buy an FL mount 28mm lens, though. I think I wouldn't worry about the effect of linear polarization. First, it might effect metering, but the instructions indicate that you might have to adjust the metering anyway. It might affect auto-focus, which you hopefully notice. Third, it affects the low-pass spatial filter, especially with Moire sensitive subjects. That might even give you extra color, but then that is why you want the filter! For most subjects, you won't have any Moire effects, anyway.
     
  2. That's pure speculation.
    I don't think that effect has ever been documented or demonstrated, and certainly not flagged as a problem likely to be encountered in real world shooting conditions.

    What was mooted in the other thread was the possibility that the 1/4 wave retarder in a circular polariser might counteract the bi-refringent element of certain low pass AA filters in digital sensors. AFAIK, that effect, as mentioned above, hasn't been shown to be a practical issue, and in any case is unrelated to the use of a plain linear polariser.
     
    Last edited: Sep 5, 2019
  3. The Wratten handbook says 'Contrast Filter, Absorbs all green, much red and less blue. Photomicrography'
    It's a part of their large laboratory set (50 filters) but doesn't make it to the small lab set (24 filters).

    The transmission spectra doesn't show anything between 460nm & 660nm.

    It might be interesting to play with on a full spectrum converted camera, as it looks like it might be like a 680nm filter with added purple & UV, but I doubt there are any cheap example around for me to play with :-(

    All the varicolour filters I have (I'm missing the blue & purple) transmit NIR, but haven't looked very good when I've tried them on full spectrum. Perhaps I'll have another play with my newer FS camera...
     
    matt_t_butler likes this.
  4. This one:

    birefringent low pass filter - Google Search

    has some explanation of birefringent low-pass filters. One separates it on one axis.

    Since the ordinary and extraordinary rays are, individually, polarized, before separating them
    on the next axis, there is a wave plate, then the IR block filter, and finally the second
    birefringent plate.

    If the incoming light is polarized on one of the axes of the first plate, that separation won't occur.
    It does seem to me that you have to be especially unlucky for this to cause problems.
    First, the linear polarizer must be close to the axis of the first birefringent plate.
    Second, the source must have a lot of high spatial frequency along the same axis.

    Otherwise, the D1 manual says:

    "The D1 cannot be used with Polar polarizing filters."

    (without saying what might happen) and:

    "When shooting with a filter attached, moire may occur ... "

    this one isn't especially obvious.
     

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