Bob Benamati's CCD Astro-Imaging Home Page

LOSMANDY G11 PE and PEMPro Results

The recent release of Gemini's L4 has provided a lot of additional functionality.  In addition to a whole new PEC implementation, some new warning messages have been experienced by users.  In my efforts to finally try and implement PEC with my G11/Gemini, I'd come across some oddities.  The first was a 'new' appearance of the "RA MOTOR LAGS" message.  Below is a screen shot of a 5 cycle run with the motor lag:

Click on the graph above to enlarge

The "Fix"

There's been some debate as to what the message means, but from what I've learned through the groups and directly through my experimentation, the "MOTOR LAG" message is commonly associated with an overloaded motor--most commonly due to an overly-tight worm to worm-gear mesh.  Well, I can confirm that the mesh does indeed make a difference.  The PE, when analyzed in PEMPro is +7.3/-8.4--much higher than my results a year before (2005). 

Post-adjustment, the PE is now a more respectable +3.2/-4.7 (below)

Click on the graph above to enlarge

So far, however, my attempts to further reduce PE with PEMPro has been unsuccessful--yet I remain hopeful, as there have been some who've reported some significant successes with the G11/Gemini--even down to around +/- 1" !!!

Unfortunately, I seem to have some sort of drift that has been wreaking havoc with my programming runs (see below--this is an UNCORRECTED DRIFT  graphic).  The PE appears fairly repeatable--some being very rapid--but oddly the first 3 worm periods had very little drift, then, suddenly and inexplicably, the drift starts....  The reported PE is +3.3/-4.0.

Click on the graph above to enlarge

JUNE 2006 UPDATE--PEC PROGRAMMING SUCCESS!

After a thorough cleaning and re-greasing, the results weren't much different--although the rapid changes in PE DID reduce significantly (so--first 'lesson learned' for me....  when PE goes up over time, first clean and regrease!).  Initial run results are below, showing a +5.1/-4.0 PE--similar to before, but the overall smoothing of the curves and the slower rate of deviation does stand out.

Click on image to enlarge

SO now for the results of PE training!

I fitted the above run using a cubic drift fit, which provided an RMS of 0.892 (THE best fit I've ever had!  Never had a fit below 1 before!).  Then, I programmed with settings of pulse modulo 35; pulse phase -2000; 10 steps, no phase shift and a guide rate of 0.2x.

The final result:  PE reduced to an unbelievable +1.0/-1.0!  The graphs are below--note that the scale is 1/3 of the pre-training file:

Click on the image above to enlarge

Now, the proof will have to be in the pudding--a real image!  More to come!

AO/TCF TUBE REFLECTION ISSUES

Original appearance

Early on, I had noticed some extreme gradients in my images.  Originally believing that the quality or technique employed in capturing my flats was to blame, I continued to image and experiment with the flats.  However, nothing was changing the outcome.  At this point, I resolved to pinpoint the problem, as it appeared to be related to internal reflections, or some other issue with the imaging train as a whole.  As I had flocked the interior of my C11 early on, this potential source was already eliminated.

Flats above were taken 1 week apart with the following:  C11 (flocked tube); ST8XE+CFW8A, AO7, OptecTCF; Optec 2" to T-thread attached directly to AO.  Stretched to enhance detail.  Notice apparent vignetting and "hot" and dark "rings".  Also note the dark spot just down from center.

Update 11/19/03

Stage 1: Flocking of AO and TCF assemblies

After some discussion on the SBIG group, and with the advice Rich Crisp, Jim Thibert and John Smith (thanks, guys!), I began the re-investigation of the issue.  After some investigation and experimentation, most of the effects appeared to be related to the AO/TCF assemblies. 

Some exhaustive flocking of the TCF 2" to T-thread tube (covering all interior surfaces), and the AO assembly interior (the scope-side 1/2 of the assembly only--no flocking done to the mirror 1/2 at this point).

                        NO FILTER                                                                                     CLEAR FILTER

It's readily apparent that a vast majority of the internal reflections have been eliminated.  However, what IS now highly visible is the internal reflection off of the clear filter.  This reflection, while less noticeable, is also present through the color filters as well.  Painting the interior tubes and the mirror half of the AO resulted in no additional reduction in the gradients seen here.

Overall, the maximum variations are in the range of 2%, and have been easy to flat-field completely from actual images--something impossible before this!

ST-Series cameras GHOSTING????

The below is a demonstration of the 'ghosting' issue with a very cold KAF chip after illumination by a bright source (star; flat field; IR illuminator of the CFW8; etc.):