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Slew and Jog Analysis (S297-305)

Pointing accuracy is particularly important for my imaging due to the relatively small AOI of my CCD chip (equivalent to just 10.4 x 15.6 arc min) and the requirement to automatically centre specific objects (eg galaxies, clusters) or carefully position both variable star and associated comparison stars within the image frame (and do this consistently session after session).   

Based on new software procedures for measuring and recording the pointing errors associated with images a dataset of 168 image sets from the last nine sessions have been analysed for telescope slew and jog performance. 

The key findings are as follows:

• Slew Accuracy across a range of targets in different parts of the sky was generally good
  with a P50 pointing accuracy of 2.3 arc min  [ mean 2.6 arc min, P10-P90 range  0.9 - 4.5 arc min ].
  
  This means that the target is placed on to the CCD chip on nearly every occasion, however it is still not optimally placed given my strict requirements.
  

• The process of automated locate image acquisition/position analysis and jog correction generally works well
  with a P50 final pointing accuracy of 0.4 arc min [ mean 0.6 arc min, P10-P90 range 0.2 - 0.9 arc min ]
  

• 73% of image sets were acquired with a pointing accuracy of below the planned accuracy target of 0.6 arc min  
  whilst 95% of images sets were acquired with a pointing accuracy of under 2 arc min.  
  

• Analysis shows that jogging (N/S followed by E/W jog) generally works wells as a means of image centering.
  Occasional retrograde performance is noted whereby the jog increases the pointing error rather than decreases it, however this does not generally detract from the overall benefit in attempting image centering.
  

• Analysis shows that the current procedure of jogging an object one final time after it has been recorded as being below the acceptable pointing threshold of 0.6 arc min, generally more and more counter-productive the closer one gets to the intended target location. In general jogging becomes counter-productive below a pointing error of around 0.3 - 0.35 arc min. This is due to the inherent limitations associated with LX200 mount at least for my older style scope, dating from 1995. 
  
  Whilst use of guide facility is particularly slow for movements in excess of 1 arc min, automated guide motion may be useful as a final operation for ultra-precision pointing (ie below 0.3 arc mins).

Graph showing Slewing Accuracy (S297-305)

Graph showing the improvement in pointing associated with locate image  acquisition/position analysis and jog correction (i.e. the beneficial impact of automated centering)

Graph showing Final Pointing Accuracy (S297-305)

Graph showing analysis of Jog Accuracy (S297-305) 225 jog operations  Y axis shows Pre-Jog Pointing Error,  X Axis shows the pointing improvement associated with the Jog Operation Positions to the right of the 'no change  zero line represent improvements in pointing. Aim of the Jog Operation is too move to a position with perfect pointing (ie zero pointing error) A pointing outcome that is within 0.6 arc min is an acceptable final outcome.

Graph showing analysis of Slew/Centering performance (2008-09-20, S303)

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