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 Notes - Session 365 (2009-04-30)

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2009-04-05
Bullet ST-10XME Linearity Testing
Bullet TPoint Mapping Attempt
Bullet Collimation Check
 
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Goto Images from 2009-04-30

ST-10XME Linearity Testing

Linearity tests where carried out on my new CCD camera (ST10-XME) using a moderately bright star. The aim was to determine the point where the KAF 3200ME CCD reached the end of its linear range and thus understand the photometric working range of the camera.

The scope was centered on star SAO 100497 (magnitude: 5.33). A sub-frame was created around the star in CCDSoft and a VB.Net routine was used to take and analyse images at progressively longer exposure times until saturation levels were reached.   Datasets were acquired for 1x1, 2x2, 3x3 binning (plus 3x3 off-chip binning)   Seeing conditions were less than ideal, with FWHM values generally around 4 to 6 arc secs (typical of my near sea level site). Datasets contain FWHM excursions up to 8-11 arc secs due to wind vibration or seeing turbulence, however the instrumental magnitudes do not appear to be too much affected.

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Instrumental magnitudes were calculated using CCDSoft's photometric calculation with aperture diameters of 24 pixels (1x1), 12 pixels (2x2) and 8 pixels (3x3), equivalent to 19.4 arc secs (~ 3.5 x FWHM).   

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Star Counts were back calculated from Instrumental magnitudes using the equation :     Star Count = 10^(Inst.Mag/-2.5) 
Resulting plots showing Total Star Count (ADU) and against exposure time are shown below.   Model lines showing linear fit to short exposure times reveal the departure from linearity in longer exposures.  The plot also shows the Maximum Pixel Value (ADU) associated with each star image.   The graphs show that 1x1, 2x2 and 3x3 datasets all seem to show  a saturation level at ~55,500 ADU.  This is a fraction below 58,300 ADU, which would corresponds to a electron saturation level of 77,000 e- (at gain of 1.32 e-/ADU). The saturation level appears to be the same regardless of degree of on-chip binning.   For off-chip binning maximum pixel value is set by the16 bit limit, i.e. 65535.  

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The graphs below show plots of  Instrumental Magnitude vs Exposure Time for each binning level. Subtracting Model Magnitude (derived from Linear Model fitted to star count from shortest exposures), reveals the estimated magnitude error associated with images that taken into the non-linear range.

 

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Converting measurements of Star Count  into a Flux (Star Count/sec) 

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TPoint Mapping Attempt 

TPoint Mapping run was attempted at the end of session S365, but wasn't completed before dawn arrived. Unfortunately only one half of the sky was mapped, and therefore the run will needed to be repeated.

The run showed that my automated mapping routine was working ok with new telescope/camera and indicated that polar alignment was pretty reasonable  (with alignment error < 4 arc minutes) 

TPoint Plots (76 points, 11 terms)

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Model Fits

  6 terms: 211 arc secs
8 terms: 107 arc secs
11 terms: 41 arc secs
 
coeff change value sigma
1 IH -49.4 -49.4 60.5
2 ID 98.8 98.8 43.9
3 NP -203.2 -203.2 28.1
4 CH 75.8 75.8 59.4
5 ME -104.5 -104.5 42.1
6 MA -19.6 -19.6 8.7
7 TF -332.6 -332.6 38.0
8 FO -147.0 -147.0 33.4
9 HDSD1 -479.7 -479.7 33.3
10 HDSH2 -45.0 -45.0 8.3
11 HHSH2 60.5 60.5 14.4

  Polar Alignment Information

6 terms:
AZIMUTH : MA: +97 seconds (+1.6 minutes).
ALTITUDE : ME: -125 seconds (-2.1 minutes).

8 terms
AZIMUTH : MA: +52 seconds (+0.9 minutes).
ALTITUDE:  ME: +170 seconds (+2.8 minutes).

11 terms
AZIMUTH : MA: +52 seconds (+0.9 minutes).
ALTITUDE:  ME: +170 seconds (+2.8 minutes)..

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Collimation Checks

Following the session collimation measurements were made on the set of T-Point automapping images using CCD Inspector 2.1.6.

The most suitable image (a well focused image with 420 well spaced stars) showed a collimation error of 20" with image curvature of 16.3%.   
Nine other images each with over 200 stars showed an average collimation error of 23" (range 17-27") with image curvature of 16.2%.

The results confirm those made during session S361 and show that the collimation changes made during session S360, were not as successful as had been initially thought, and probably indicate the reason why FWHM measurements of no better than 4.0 arc secs have been achieved during the last few sessions.

Collimation Checks  (S365)

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Image with numerous well spaced stars 
used for Collimation / Curvature Check
(measurements shown by the circled point in the graphs above)
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CCD Image with Stars used by CCD Inspector
 5 sec exposure (single frame), 3x3 binning, C Filter 
2009-05-01 02:22 h UT  (#365138)
12" LX200R  (at f/5.7) + ST-10XME

 

Curvature Measurement for 12" LX200R  with f6.3 focal reducer - 2009-05-01
 Curvature 16.3%
 (420 stars used,, scope operating at f/5.7)

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CCD Inspector plot 
Image details as above (#365138)

 

Collimation Measurement  - 2009-05-01
420 stars used, collimation 19.5"

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CCD Inspector plot 
Image details as above (#365138)

 

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

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

 

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

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CCD Inspector plot 
15s sec exposure, 2x2 binning, C Filter (#360292)
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 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
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
S365  5s 420 15% 16.3%  19.9" 4.7"   +0.5"   +0.0"    10% @ +3 deg
S365  10 x 5s 277 +/- 68 17% +/- 5% 16 .3% +/- 0.2% 23.1 +/- 3.4" 5.0" +/- 0.7"   +0.5" +/- 0.2"   +0.1" +/- 0.2"   11% @ -15 deg

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This Web Page: Notes - Session 365 (2009-04-30)
Last Updated : 2015-05-16
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