NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2011 Oct 3, 14:32 -0700
It has been a few years now since my first DSLR camera CN observations. The final evolution has a solar film strip held in place between two empty lens filter frames and capped off with a UV filter to protect both the lens and solar film from ocean spray and sand. This arrangement makes camera CN observations no more difficult than taking a regular picture while on manual mode. Focus must always stay on infinite. A strip of electricians tape works good to secure at infinite. There is flexibility in both the F stop setting and shutter speed. A high F stop (longer focal length) produces a sharper horizon. Shutter speed needs to be fast enough to eliminate hand shake. 1/100 of a second is good on land. 1/400 of a second is good at sea.
Photo editing a Sun CN image has been modified some for practical use. Cropping an image through the center of the Sun and at the horizon then fine tuning the crop lines on a magnified view edit setting does a consistent quick job of determining pixel height of the body center above the horizon. The minutes of arc per pixel graph is kept on my laptop desk top for the final conversion to sextant altitude (Hs).
Timing is done by setting the camera clock to the second then checking by photographing the face of the chronometer. This time stamping method has been working well since day one.
See linked images:
1. IMG2548 Raw 3888px by 2588px unedited UT 00:16:12 10/3/2011 for those interested in trying an edit, crop, and sight reduction.
2. Edited and cropped IMG2550 at 2590 pixels.
3. Edited image showing crop lines through horizon and Sun.(picture 145)
4. Index card MOA/Pixel table. Kept in the camera bag and used when using someone elses computer. Requires interpolation.
5. Index card working notes for image 2548.
6. Front veiw of camera and solar filter.
7. Profile veiw of camera and solar filter.
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