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07-28-2011, 07:54 PM   #1
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Interesting GPS astrotracer mathematics.

What the astrotracer function does is simply to keep startrails out of the picture. Those startrails happen because the earth is rotating 15 seconds of arc each second of time. What the gps does is move the sensor in the camera to compensate this startrailing which makes a star picture elongated. To emulate an equatorial mount, the sensor has to move up and down, sideways and also rotate. We are tempted to think that these movements have to be big but that's not the case at all. I have done some calculations for the worst case which is a star on the horizon. The biggest sideways movement that the sensor has to do would be 1.19 mm which is not a lot. The formula for startrails at the horizon is (Lens focal length X exposure time in seconds X .00007). I have used the data given by Pentax for the astrotracer function. What I find fascinating is the huge amount of calculations that the software inside the camera has to do to correct the three movements of the sensor, it's simply incredible that it works at all. Correct me if I'm wrong. Comments appreciated.

08-03-2011, 06:50 PM   #2
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I agree, it's a lot of number crunching... and of course the numbers change with latitiude, the star being "looked" at, the angle relative to North....


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