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Subject: Kids in exchange of 16 "
From: DK0179@AppleLink.Apple.COM
Reply To: mapug@shore.net
Date: Thu Apr 06 01:49:00 1995

Thanks to Dennis diCicco, and Jason for useful comments. .. I really appreciate your reactions, below you find my comments, Dennis, please do not send any neighbour kids... < Furthermore, I'm assuming his images were brief enough not to saturate the <detector (Procyon is blindingly bright to a CCD), which could affect the <accuracy of the centroiding of the image. All images were taken in blue filter, short exposure times, below saturation limit. The telescope was well focused too, seeing good. <At the 4-meter focal length of the 16", the 23 x 27 micron pixels of the <ST-6 camera cover 1.2 x 1.4 arc seconds of sky. I'm quite certain the <long dimension was aligned with right ascension. Taking Winther's list of <centroid positions at face value, we see a 28.37-pixel drift in 14 <minutes. This works out to 39.7 arc SECONDS . <Winther doesn't say if the scope was running fast or slow and I can't <tell for sure from the data since it would be reversed if the camera <were on a star diagonal (which I've see a lot of people use). The CCD was mounted directly, without any diagonal, as close to the telescope as possible, avoiding flexure problems. <If the scope were running slow, this 2.8 arc minute drift per hour is just <about what I'd expect if the scope were tracking at solar rather <than sidereal rate. The star was moving eastward, indicating a westward telescope moving. The telescope was thus running TOO FAST. The hand key indicated a correct tracking rate, a sidereal rate 60.1 Hz, this is also the default rate during start up. I have tested the clock, it seems stable within 15 seconds a day. I am happy that the drift is so nice, but have two questions : 1. Do I now have to decrease the tracking rate, from stellar rate, to e.g. an even higher rate (1 digit, e.g. 60.2 is the only possible) - in order to get the correct movement ? I have spent hundreds of hours making this observatory run, and do not mind if I have to adjust this default rate during each startup, but I know my students and my collegues will mess this up/ forget this correction. - and the next three questions, which I hope Meade will comment : 2. Is this a simple programming error , e.g. a factory based smart drive, being calculated from an artificial star, running at the wrong solar rate ? 3. Why is the smart drive on these 16 " SCT-s closed to the user ? Smaller instruments have the possibility of RA-learn, but the 16 " does not have this feature, not even in polar mode. If this smart drive feature RA learn had been open to user, as it is on cheaper telescopes, we would have solved the problem ourself. I expect the combination of RA learn and CCD, and our problem would easily correct this drift during one single autoguide run. 4. The DEC learn is present on the 16 ", but the RA learn was not. Are there any plans involving this RA-learn feature -present on simple telescopes- on the 16 " too ? Best regards, Mogens Winther and students, Amtsgymnasiet in Sonderborg Grundyvigsalle 86 6400 Sonderborg, Denmark.