autoguiding – a deep look · 2016. 5. 3. · autoguiding – a deep look andrás dán, msc,...
TRANSCRIPT
![Page 1: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/1.jpg)
Autoguiding – a Deep Look
András Dán, MSc, Hungary
CEDIC, Linz, April 2009.
![Page 2: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/2.jpg)
Why is Autoguiding needed?
Unguided imaging is nice, but:
• Periodic Error
• Polar alignment
• Flexture
• Refraction
May limit exposure time/resolutionMay limit exposure time/resolutionMay limit exposure time/resolutionMay limit exposure time/resolutionMay limit exposure time/resolutionMay limit exposure time/resolutionMay limit exposure time/resolutionMay limit exposure time/resolution
![Page 3: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/3.jpg)
Do we need long exposures at all?
YES, because we have:
• Narrow band filters
• Low surface brightness objects
• Multifilter image acquisition that lasts several nights
![Page 4: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/4.jpg)
Tracking in RA(for 2-3 sec intervals)
Error
Source
Typical
value (arcsec)
Characteristics Relative
value
PE+Drift 0,1- 0,4 systematic 10 - 40%
Flexture 0 - 0,02 semi-
systematic
Seeing 0,5 - 2 random 90 - 60%
![Page 5: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/5.jpg)
Gemini G42, no PEC, poor seeing
![Page 6: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/6.jpg)
Tracking in DEC
Error
Source
Typical
value (arcsec)
Characteristics Relative
value
Drift 0 – 0,2 Systematic 10 – 40%
Flexture 0 – 0,05 Semi
systematic
Seeing 0,5 - 2 Random 90 – 60%
RA bearing 0,1 - 2 Random
![Page 7: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/7.jpg)
How about encoder controlled drives?
•• Ensure subarcsecond precision for Ensure subarcsecond precision for 1010--20 minutes 20 minutes –– of RA axis rotationof RA axis rotation
•• Do not correct Do not correct flexture, drift and flexture, drift and refractionrefraction
![Page 8: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/8.jpg)
Autoguiding parameters
»1 Calibration
Done under constant speed – used in acceleration
This ensures a slight undercorrection.
![Page 9: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/9.jpg)
Autoguiding parameters
»2 Guidestar quality
An aberrated or dim stellar image gives unreliable centroid values.
E.g.: off axis situations
![Page 10: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/10.jpg)
Autoguiding parameters
»3 Exposure time
• Longer – reduces seeing effects
• Shorter – corrects PE better
![Page 11: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/11.jpg)
Autoguiding parameters
• 4 Agressiveness
Compensates seeing and calibration problems.
• 5 Pause after correction
Helps to avoid oscillations.
![Page 12: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/12.jpg)
Current Practicesof Autoguiding
• Guidescope
Flexible star selection – flexture
• Off-Axis
Good rigidity – small field
![Page 13: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/13.jpg)
Example - guidescope
![Page 14: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/14.jpg)
Example – Off axis
![Page 15: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/15.jpg)
Current Practices
• Dual Chip
Highest rigidity – filter problem
• Interline Transfer Chip
Simplest solution – image noise
![Page 16: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/16.jpg)
Current Practices
• Active optics
Best results – backfocus problems, camera choice limited
![Page 17: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/17.jpg)
Practical Tips
• Minimize flexture
Small weight, reinforcements, quality focusser
• Use threaded or conic interfaces
![Page 18: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/18.jpg)
![Page 19: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/19.jpg)
Practical Tips
• PEC active
Longer exposure, less seeing effects
• Small aperture guidescope
Up to 10cm the seeing is always fair
![Page 20: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/20.jpg)
Romulo de Luna F.
Gemini G42
6” PE
1” PE
![Page 21: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/21.jpg)
Trailed Stars – What shall I do?
• Direction of the trail
E-W, N-S, Other
• Set of short expos with intervals
3s expo, 60sec pause, 15 times
(guiding ON)
![Page 22: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/22.jpg)
Trailed Stars
• Compare 1 worm cycle guided and
unguided exposures
• Make startrail images (30”/min drift)
![Page 23: Autoguiding – a Deep Look · 2016. 5. 3. · Autoguiding – a Deep Look András Dán, MSc, Hungary CEDIC, Linz, April 2009](https://reader033.vdocuments.us/reader033/viewer/2022061001/60b0432f8f258772cd13108d/html5/thumbnails/23.jpg)
Images courtesy of
• Althoff, Gerd
• Kerschuber, Günther
• Mori, Eiji
• Tangen, Oivind
• Freire, Romulo de Luna
In order of appearance.
Thank you for your attention!