David's Astronomy Pages
 Notes - Session 359 (2009-03-29)

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(S360) 		 
2009-03-29
Bullet Restart from Park Position
Bullet Polar Alignment Checks
Bullet Tracking Rate Adjustment Trials
Bullet PEC Training
Bullet Automated Filter Adjusted Focusing - M13
Bullet Collimation and Image Curvatures Measurements
 
>

Goto Images from 2009-03-29

Restart from Park Position  

Start up from Park. GPS fix achieved after 10 asterisks. Usual fix after 3 to 7 - is the longer fix this time because it's 01:40 h local time and GPS satellite coverage is lower ?

Slewed from Park Position to Regulus and took this 3 sec snap.  The star is pretty much centered and a re-sync could be ignored. 

Regulus (Leo)
Snap Shot Image after slewing to star from Park Position
The vertical blooming  streak is normal feature associated with
 imaging bright star with Non-ABG CCD camera
Image
CCD Image (52% size reduction) with Cross Hairs
3s (single frame), 3x3 binning, C Filter
2009-03-29 01:40 h UT (#snap 0140-54)
12" LX200R  (at f/5.7) + ST-10XME
  
Regulus - with circular light artifact surrounding star 
Image
CCD Image (52% size reduction) 
Image details as above
adjusted black/white range 

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Polar Alignment Checks 

A short Drift Align check were made to confirm previous measures of the accuracy of the telescope's Polar Alignment and test for star drift with Tracking Rate Adjusted to +1 setting

The N-S drift of a star in the Southern Sky (near to Meridian & Declination 0)  were measured from images taken approximately 12 minutes apart.  
Images pairs - Binning 2x2, Plate Scale 1.612, Exposure 10 secs.


This Session (S359)
N-S Star Drift : 0.29 arc secs/min NORTHWARDS (Polar axis pointing 1.12 arc mins too far west - requiring that wedge is  rotated very slightly clockwise)

Previous Session (S358)
N-S Star Drift : 0.27 arc secs/min NORTHWARDS (Polar axis pointing 1.04 arc mins too far west - requiring that wedge is  rotated very slightly clockwise)

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Tracking Rate Adjustment Trials 

Image Pair created for the Drift Align Check also indicate that stars are drifting westwards by 16.6 pixels in 12.07 minutes (at 1.611 arc sec/px).  This is equivalent to a rate of 2.2 arc sec/minute,  but is subject to significant uncertainty due to Periodic Error as PEC was turned off at the time.

Session  Tracking Rate
Adjustment		 Star Drift (in RA)    Actual Tracking Rate
   Notes
S356/357  'Sidereal' Westwards by 1.9 arc secs/minute Slow by 0.21%   South Sky Point (w/o Pec)
S358a 'Sidereal'   Westwards by 3.2 arc secs/minute Slow by 0.34% South Sky Point (with Pec)
Westwards by 4.1 arc secs/minute Slow by 0.34% West Sky Point (with Pec)
S358b  +3  Eastwards by 2.5 arc secs/minute Fast by 0.28% South Sky Point (with Pec) 
S359  +1 Westwards by 2.2 arc secs/minute Slow by 0.24% South Sky Point (w/o Pec)

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PEC Training / PEMPro evaluation

PEC training was attempted using an evaluation copy of PEMPro v2.6

PEMPro acquiring data, using ST-10XME camera/via CCDSoft

(Although the PEC indicator shows that PEC was "ON" during the acquistion run, the LX200R's PE table 
was in fact empty (all zeros) and therefore the scope behaved as if PEC was OFF)
Image
PEMPro acquiring data from second 24 minute cycle
Image
All data
Image
Creating the PE Curve 

PE Curves were examined with different Drift Fittings (from First to Fifth Order). They show dereasing RMS Error with Order,
ranging from 2.437 to 1.837.

Drift Fitting   Periodic Error   RMS Error
1st Order -Linear  +15.5 / -14.5  2.437
2nd Order - Quadratic   +15.6 / -14.5  2.374
3rd Order - Cubic  +15.8 / -14.8  2.159
4th Order - Quadratic  +15.8 / -14.6  2.072
5th Order  +15.2 / -14.0  1.837

The Fifth Order curve has lowest RMS, but risks optimising out some of the periodic error, since I had 
only 2-3/4 cycles worth of data. The Quadratic Drift Fitting was therefore used.

Graphs of Data and Fitted PE Curve are shown below. 

Image 
 
Shown below is PE curve (quadratic drift fitting) with and without data points
Image 
Image 
 

PEMPro allows the different frequencies involved in the Periodic Error to be identified and quantified.  
Graphs of Frequency Spectrum show that the main frequencies are
  3:  (3 cycles/worm period)  8 minute period
  1:  (1  cycle/worm period)   24 min period
  6:  (6 cycles/worm period)  2 cycles per 8 min period
  9:  (9 cycles/worm period)  3 cycles per 8 min period
  4:  (4 cycles/worm period) 
  8:  (8 cycles/worm period)  2-2/3 cycles per 8 min period
x3:  (mutiples of 3 cycles/worm period :  6, 9, 12, 18, 24, 27. 30, (33), 36 (39), 42, 45, 48, 60, 75 cycles per 24 min period
 5:  (5 cycles/worm period)   1-2/3 cycles per 8 min period
20:  (20 cycles/worm period) 6-2/3 cycles per 8 min period

Testing PE curve with different Fundamental Frequencies

Image

To explore the influence for different Fundamental Frequencies, the PE curve was examined with different combinations of frequency.

Testing PE curve with different Fundamental Frequencies

 Image
 

PEMPro has the ability to upload the PE curve directly to LX200GPS and LX200R scopes. However during the live session the wrong route was taken and I began playing back the curve to the Mount.  This took 24 minutes to perform and was completely in vain as the LX200 Autostar II was not setup in PEC training mode.  As a result the scope was still left without the PE table. 

This was corrected during the start of the next session when the PE curve was directly uploaded to the LX200R scope. The process  just took a few seconds to complete.  Downloading the PE curve from the scope and comparing it with the original PE curve showed that the upload had been successfully received,

PEMPro- created PE curve and playing back curve to Mount
(Peak to Peak PE : 29.7 arc secs)

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Automated Filter Adjusted Focusing - M13

M13 taken through different Filters using CFW10 Filter Wheel

Focus position is automatically adjusted between frames by 
sending appropriate focus step offsets to the Optec TCF-S focuser.

Image
CCD Image Montage 
10-45s exposures (single frames), 3x3 binning, Various Filters
2009-03-29 (#359012-29), 12" LX200R  (at f/5.8) + ST-10XME
 
Focus Offsets for the CFW10 filter set at f/5.6 (defined 2009-03-16)
  Image
 
Previous images of M13 taken on First Light Session - 2009-03-09

Filtered Images all taken at the same focuser position
 Red, Green, Blue and Spectral images are significantly out of focus.

Image
CCD Image Montage 
10-30s exposures (single frames), 3x3 binning, Various Filters
(Images are all taken using the same Focus Position)
2009-03-09 (#356188-237),  12" LX200R  (at f/5.8) + ST-10XME

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Collimation and Image Curvatures Measurements

An evaluation copy of CCD Inspector 2.1.6 (by CCDWare) was used to review collimation quality of images taken during the first 3 sessions with the new Imaging Setup.
The figures below indicate an initial collimation error of around 35-42". , which was only slightly improved by the 'manual' re-collimation attempt in session 357.
(The main difference pre- and post re-collimation was the the collimation error flipped from one side of the CCD to the other)

The figures reveal a curvature value of 16-27%. This is a relatively low number and shows the improvement of Meade's ACF (R) optical design over the standard SCT design.

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 Collimation 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



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This Web Page: Notes - Session 359 (2009-03-29)
Last Updated : 2015-05-16
Site Owner : David Richards
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