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08-29-2016, 08:56 AM   #16
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QuoteOriginally posted by PhilRich Quote
So, if using a zoom lens, the camera doesn't calculate compensation for focal length changes?
It will compensate for the zoom, unless it's an old lens that doesn't report the focal length camera, in which case you will have to manually enter the focal length.

08-29-2016, 11:19 AM - 1 Like   #17
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QuoteOriginally posted by PhilRich Quote
So, if using a zoom lens, the camera doesn't calculate compensation for focal length changes?
The point of the calibration is to measure the strength and direction of the magnetic field as affected by all the stuff in or near the camera. If the zoom lens contains steel parts (e.g., retaining rings, springs, cams, clips, aperture blades, motors, etc.) those will affect the magnetic field and if those steel parts are on the zooming parts of the lens, then zooming may change the magnetic field environment. Whether it's enough to really affect the shot is a complex function of many variables but the best thing to do is to calibrate with everything configured as close to the intended shooting conditions as possible.

Astrotracer does use the reported focal length of lenses that send that info to the camera so the optical effects of zooming are accounted for. But if zooming affects the magnetic field, and you zoom after the calibration, then the camera may think it's pointed a few degrees different than it is and not properly correct for the motion of the stars.
08-29-2016, 11:46 AM   #18
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It seems impossible to get a better accuracy then +-15 degrees, so I made an experiment.

I turned the camera in the direction where the error was the largest, I then taped a piece of a metal paperclip on top of the prism house in such a way that the error was minimized. Then I turned the camera to the new largest error which where about 90 degrees from the original one and again I taped another piece of the paperclip on top of the prism house in such way so that the error was minimized.

And now the error was down to +-5 degrees in any direction. Success, and I figured that maybe I should do something more portable that could be attached and removed sitting in the flash shoe.

But then I tried a new calibration with the compensation clips still attached, and unfortunately the original error was back. My compensation clips where compensated for.

Back to the drawing board. Hm, maybe an adjustable metal bar on top of the prism house that I can rotate until the compass shows exactly the heading I want... Not pretty but maybe it can improve the astro tracker performance?
08-29-2016, 12:20 PM   #19
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Thanks for these thoughts. Didn't think about all moving metallic parts at all...

08-30-2016, 10:30 AM   #20
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Does the K-1 display the compass heading? If so, where, I've been looking for it. Thanks.
08-30-2016, 11:06 AM   #21
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Yes it can, press info button twice to get to the display options, then step to the rightmost option for electronic compass and hit ok.
Note that this will also turn on the GPS.
08-30-2016, 01:23 PM   #22
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QuoteOriginally posted by Gimbal Quote
Yes it can, press info button twice to get to the display options, then step to the rightmost option for electronic compass and hit ok.
Note that this will also turn on the GPS.
Thanks for the quick reply!!
08-30-2016, 03:57 PM   #23
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QuoteOriginally posted by PhilRich Quote
Does the K-1 display the compass heading? If so, where, I've been looking for it. Thanks.
Easiest way is press Info, press Info again, select Compass Display (rightmost choice).

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