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Notes - Session 382 (2009-08-07)

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2009-08-07
Bullet Collimation Check
Bullet Focuser Coefficients, 12" LX200R operating at f/5.7
 
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Goto Images from 2009-08-07


Collimation Checks

Night of good seeing.  Collimation checks were made to see why image quality has been generally poor. 

 poorer seen collimation  was performed at the end of the last session (S360). Final estimated collimation error was around 3 - 4 arc secs, compared to a immediately prior collimation error of 14 arc secs (and compared against original first light collimation error of around 35-42 arc secs). It was unclear why the collimation error immediately prior to re-collimation attempt (14 arc secs) was rather less than the measurements made during session S358 (31-37 arc secs)  (Mirror slop ?, seeing).

To investigate the collimation behavior of the scope, a collimation check was made on a star field lying at around 52 deg altitude.  Collimation error (20-25 arc sec) appears to have increased from that shown in the last session, but is still lower then measurements made during S358.   It would seem that whilst sub-5 arc sec collimation was not reliable, a 10 arc secs improvement was nevertheless made. 

Collimation Measurement  - 2009-04-01 (post Re-Collimation)

Image

CCD Inspector plot 
15s sec exposure, 2x2 binning, C Filter (#360292)
12" LX200R  (at f/5.7) + ST-10XME

  

Collimation Check  - 2009-04-05
(collimation has appeared to have degraded)

Image

CCD Inspector plot 
20s sec exposure, 2x2 binning, C Filter (#361021)
12" LX200R  (at f/5.7) + ST-10XME

  

Table of Collimation / Curvature Measurements  - 12" LX200R  (at f/5.7) + ST-10XME

Session  Images Stars
Aspect
Ratio
Curvature
   Collimation 
(arc secs)
   Average FWHM
(arc secs)
   Tilt X    Tilt Y    Total Tilt
S356 (First Light Session)  30 x 30s 148 +/- 13 38 % +/- 20% 16 % +/- 1% 41.6" +/- 6.3" 5.4" +/- 0.7"   -0.9" +/- 0.1"   -0.3" +/- 0.1"   16% @ -157 deg
S356 (First Light Session)  6 x 60s 410 +/- 22 38 % +/- 10% 27 % +/- 1% 35.0" +/- 6.5" 5.3" +/- 0.3"   -1.1" +/- 0.2"   +0.5" +/- 0.1"   20% @ -149 deg
S357 collimination attempt
S358  7 x 90s 575 +/- 40 19% +/- 8% 24 % +/- 2% 36.3" +/- 6.3" 5.5" +/- 0.4"   +0.9" +/- 0.2"   +0.1" +/- 0.1"   15% @ - 5 deg
S358  6 x 45s 633 +/- 73 14% +/- 3% 21 % +/- 2% 31.7" +/- 7.6" 4.9" +/- 0.4"   +0.7" +/- 0.2"   +0.3" +/- 0.1"   10% @ - 22 deg
S358  3 x 60s 695 +/- 80 16% +/- 6% 24 % +/- 1% 36.1 +/- 4.0" 5.9" +/- 0.6"   +0.9" +/- 0.1"   +0.1" +/- 0.0"   14% @ - 9 deg
S360  2 x 20s 199 +/- 1 16% +/- 4% 22 % +/- 3% 13.9 +/- 1.3" 4.0" +/- 0.2"   +0.6" +/- 0.1"   +0.0" +/- 1.0"   12% @ - 9 deg
S360  3 x 20s 184 +/- 27 27% +/- 5% 24 % +/- 6% 14.7 +/- 1.5" 4.2" +/- 0.3"   +0.5" +/- 0.1"   -0.1" +/- 0.1"   12% @ 19 deg
S360 - Collimation attempt
S360 - Post Collimation 4 x 20s 223 +/- 13 17% +/- 1% 17 % +/- 3% 3.7 +/- 1.0" 4.0" +/- 0.1"   +0.2" +/- 0.1"   -0.1" +/- 0.1"   4% @ 20 deg
S361  2 x 20s 412 +/- 65 14% +/- 1% 22 % +/- 1% 25.1 +/- 5.7" 4.5" +/- 0.1"   +0.8" +/- 0.1"   -0.4" +/- 0.1"   15% @ -33 deg
S382  (Alt 33 deg) 2 x 5s R 271 +/- 8 17% +/- 2% 22 % +/- 1% 37.9 +/- 2.0" 3.6" +/- 0.1"   +1.0" +/- 0.1"   0.7" +/- 0.1"  
S382  (Alt 51 deg) 2 x 20s VR 322 +/- 32 18% +/- 6% 18 % +/- 2% 26.1 +/- 8.3" 3.4" +/- 0.2"   +0.8" +/- 0.2"   0.4" +/- 0.2"  
S382  (Alt 65 deg) 2 x 5s R 113 +/- 7 12% +/- 2% 26 % +/- 2% 21.6 +/- 4.1" 3.1" +/- 0.1"   +0.7" +/- 0.1"   0.4" +/- 0.1"  

 

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Focuser Coefficients, 12" LX200R operating at f/5.7

Focus positions for the C Filter were collected over an 18 degC temperature range of the course of several observatory sessions (Primary mirror locked in same position throughout)
The dataset is plotted below. Best fit line indicates

The dataset shows considerable scatter and a session specific adjustment to datum focus position is frequently required to account for night to night changes in best focus. A clear reason for this has not yet been determined

Image

 

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