Re: Adjust CP4 Clock Frequency

Roland Christen

If you are seeing a 0.1% error in your basic Sidereal tracking rate (assuming that you have polar alignment for min drift pointing straight up) then something is definitely wrong and you should make arrangements to send the RA axis and your controller in so we can check it out.

You can do this test and report the results:
1) point the scope straight up with counterweights in the West. Check the drift rate of a star for 60 seconds, or better yet 5 minutes, in RA.
2) repeat the test with the counterweights in the East.
Note the drift rate as + or -.
3) send the scope to a star toward the eastern horizon and note the drift rate in Dec.

Roland Christen

-----Original Message-----
From: Craig Young <craig.young.m8@...>
Sent: Tue, May 5, 2020 5:50 pm
Subject: Re: [ap-gto] Adjust CP4 Clock Frequency

If the Sidereal rate is 15 arcsec/second then a 60 second image will have a movement of 15 x 60 = 900 arcseconds.  If the error is 0.001 then the drift will be 900 x 0.001 = 0.9 arc seconds which is about 2 pixels on my plate scale.  A 5 minute image will then be 0.9 x 5 = 4.5 arc seconds .. or about 10 pixels .. this is what I am seeing.  But what if the drift is lower than this .. say 0.0001 then the tape measurement must be accurate to 0.05mm.  I think when a mount of this calibre has encoders (at over $6000 cost) and can easily determine pulses per period of time .. why don't we have this?  This is not confidential information, just a simple metric to make sure everything is calibrated properly.  I think using a piece of tape is not the method a mount of this calibre deserves.


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