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    Re: 35mm Super Takumar Lens for CN on DSLR
    From: Greg Rudzinski
    Date: 2015 Aug 10, 16:51 -0700


    I calibrate using the Sun and an H20 artificial horizon for high altitudes. For lower altitudes a natural horizon from the beach at a height of eye of 7 ft. is used. A timed image is taken every 2 minutes of time on the artificial horizon and every 4 minutes for the natural horizon. A sight reduction is worked up for each image from a known position to get a zero intercept. Minutes of arc per pixel is determined for the measured pixel spread. The 35mm lens on a Canon Rebel 10MP DSLR will have about .57' per pixel multiplier plus or minus a correction in minutes of arc. The full set of corrections can be graphed so that any pixel spread will give an Hs. I will be posting results when horizon and sky permit. Focus has to be at infinite to maintain a fixed focal length. ISO, f-stop, and shutter speed are free to vary. It is best to favor a fast shutter speed. 

    Greg Rudzinski

    From: Norm Goldblatt
    Date: 2015 Aug 9, 21:50 -0700

    I'd love to know how you calibrate.  Star field? Calibration target? If target, I wonder if calibration would be reliable at finite distance. Obviously, the target has to be reasonably close to be practical.   I tried using Ursa Major and found that either I made some mistakes or the iphone 5 optics produce a miserably distorted field (at least for CN). 


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