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    Re: Simplified Bris Sextant (calibration)
    From: Greg Rudzinski
    Date: 2012 May 12, 10:10 -0700

    Here is complete calibration data for 8 digital camera images taken through the Simple Bris Sextant as the horizon was observed passing just under the the center of the Sun. ( 1 pixel = 0.38')

    Lat. 34* 9.8' N Lon. 119* 13.8' W H.E. 8.5 ft.
    UT Date 5/12/2012
    UT 01:17:26 Hs 17* 24.9' corr. (-1.5' for 4 pixels) 17* 23.4' calibrated altitude
    01:17:23 17* 25.5' (-1.9' for 5 pixels) 17* 23.4'
    01:17:21 17* 25.9' (-2.3' for 6 pixels) 17* 23.6'
    01:17:18 17* 26.5' (-2.3' for 6 pixels) 17* 24.2'
    01:17:16 17* 26.9' (-2.7' for 7 pixels) 17* 24.2'
    01:17:13 17* 27.5' (-3.8' for10pixels) 17* 23.7'
    01:17:11 17* 27.9' (-4.2' for11pixels) 17* 23.7'
    01:17:09 17* 28.3' (-4.6' for12pixels) 17* 23.7'

    Avg. 17* 23.7' calibration altitude
    Spread 0.8'

    I am satisfied with these results and will be using this calibration value for future observations made with the Simple Bris Sextant.

    Greg Rudzinski

    [NavList] Re: Simplified Bris Sextant (calibration)
    From: Greg Rudzinski
    Date: 11 May 2012 21:05
    Todays afternoon calibration of the Simplified Bris Sextant was recorded with a 50 mm lens vs. the 200 mm lens used two days ago and made the picture taking of the Sun's center on the horizon easier because of the larger field of view as well as being lighter to hold. What looked like a horizon spitting the Sun in the camera view finder turned out to be 5 pixels (1.9') low of center when the image was blown up in iPhoto. This means the zero intercept (Hs) altitude for the marked time gets reduced by 1.9' for a corrected calibration value of 17* 23.0'. This value is 1' higher than the calibration done with the 200 mm lens. So I'm thinking that both calibrations are close to the truth.

    It must be quite a chore to calibrate all the Suns on an original Bris Sextant. My sympathies go out to those who have one ;-)

    Greg Rudzinski

    [NavList] Re: Simplified Bris Sextant
    From: Greg Rudzinski
    Date: 9 May 2012 21:57
    The calibration observation came in at PDT 18:16:26 (IMG 3508) and worked out to 17* 22'. The spread for this Bris seems to be about 7'. Using the limbs as the reference is not as good as splitting the middle of the Sun's image. I made the calibration task harder than it needed to be by using a 200mm telephoto lens to document the moment. The 50mm would have been better.

    Greg Rudzinski

    [NavList] Re: Simplified Bris Sextant
    From: Greg Rudzinski
    Date: 9 May 2012 09:51
    The 50 mm DSLR calibration for the Bris Sextant derivative came in at 17* 15.6'. This puts me on the beach at 18:16 today PDT +7. It will be interesting to see how close the camera rough calibration compares to an actual horizon calibration. ( IMG 3462 shows Actual and reflected Sun overexposed)

    Greg Rudzinski
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