Odd tracking/guiding behavior

Mike Shade

Have an issue with RA tracking/guiding. 


-1600GTO, have greased RA and DEC, set gear mesh, trained innumerable PEC curves.  CP4 electronics, there have been no software upgrades to the CP4.  The CP4 is an early one, I think around May 2016. 

-Planewave CDK 17, Optec Gemini focuser/rotator.  Attachment is extension tubes (solid).

-SBIG STL 6303E, Astro-Don 50mm LRGB filters, unbinned imaging scale .632"/pixel

-Windows 7 system, Maxim 5.18, Focusmax (older free version), latest V2 driver, ACP 8, Sky6.  This is an automated system.  Running serial cable to mount, replaced recently (with AP supplied cable).

-System permanently mounted, polar aligned in observatory.  Seeing here runs 2" +/-.  Reasonably dark skies.

-Guiding through the guider relays.  Recently replaced guider cable and guider "dongle" on camera.  Guider calibrates fine, every time, with a 40 pixel movement.  Returns guide star to starting point on calibration.

-Scope balance slightly off in RA and DEC (slightly to load gears).

-Guide exposure is 10", aggressiveness of 7, guider binned 3x3

-I run 10' luminance exposures

-There have been no software upgrades (other than V2), equipment changes, reconfigurations.

-I have checked for cable drag or snag

-Checked connections, bolts, fasteners and such on OTA and imaging train, unguided short duration images at 30, 45, and zenith do NOT show any collimation changes.


What I am seeing on images are intermittent double images or streaked images.  There will be a star and "streaks" where the star moved off and was moved back (almost like tadpoles if this makes sense).  This is ALWAYS in RA, it is NOT on every image, it is intermittent.  I can look at the guider logs and see BIG jumps in RA for a ruined image.  For example the log says displacement of....32, -.05, .21, 6.35, 2.6, 1.8, .52, -.08  The images show this displacement with the tadpoles.  This is not constant though meaning that it is not "every 5.3 minutes there is a big jump"...very very intermittent.


I have seen this before, very rarely in the past and chalked it up to...whoops...it is now becoming more frequent but not constant.  In addition, many (but not all)  images are slightly "off" in RA...maybe a pixel or two, always in RA, just enough to say "that star is not quite round".  Watching the guiding graph in Maxim shows DEC steady, RA not so much.  Very very rarely I can see a big jump in RA (I have an automated system so I don't have to watch the system all night). 


And yes, I have made sure the PEC curve is on and is not inverted.  It is always in RA.  I have checked that there is no wind, clouds.  These images are not at a low elevation.  There were two from last night's run that were streaked, elevation was 55 degrees or so.  Images higher up show a slight out of round in RA...slight.


I know this is pretty vague but...At this point thinking of popping my original CP3 back on and seeing if this helps...


Any other ideas of checks?


Mike J. Shade: mshade@q.com

Mike J. Shade Photography:



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In Defeat: Defiance

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