Image Acquisition Best Practices. Richard A. Bennion Ewell Observatory

Transcription

1 Image Acquisition Best Practices Richard A. Bennion Ewell Observatory

2 QTR MILE: 16.2 QTR MILE:

3 Imaging Performance By what standard do we measure imaging performance? What is good data vs. bad data? We can take better images! The information we need is everywhere. But where is this information

4 The Secret is in the Stars

5 The Secret is in the Stars

6 Measuring Stellar Profiles - FWHM Full Width at at Half Maximum Measured in in Pixels FWHM: 4.8 PIXELS Determine Peak Brightness of of Star ADU: Convert Pixels to to Arc-Seconds (4.8 pixels * arc-seconds per pixel) FWHM: 2.40 ARC-SECONDS HALF MAXIMUM (50%) MAXIMUM Determine Background Brightness ADU: 1829

7 The Stellar Profile Effects on Resolution FWHM:

8 When We Don t Get Good Images, One Or More Of These Is The Culprit! Atmosphere Optics Optics Focus Focus Tracking

9 The Atmosphere Some things out of our control

10 Atmospheric Seeing

11 Imaging Through the Atmosphere FWHM: 3.0 FWHM: 2.5 FWHM: 2.1 FWHM: 1.9

12 Optics A little attention goes a long way

13 Optical Performance Mis-Collimation FWHM: 2.95 ARC-SECONDS Celestron C11 & ST10XME

14 Optical Performance Hyper Collimation FWHM: 1.95 ARC-SECONDS Celestron C11 & ST10XME 5º Degree Turn: 1.00 Decrease in FWHM

15 Optical Performance Why are the stars not the same size? FWHM: 3.15 FWHM: 2.20 FWHM: 1.95 Celestron C11 & ST10XME

16 Optical Performance Field Curvature FWHM: 3.13 FWHM: 1.95 Celestron C11 & ST10XME

17 Optical Performance Field Curvature CURVATURE: 48.6% CURVATURE: 4.9% Celestron C11 & ST10XME Takahashi FSQ-106 & ST11000XM

18 Optical Performance Field Flatteners CURVATURE: 22% 14.5 RCOS & 6303 CURVATURE: 7% 14.5 RCOS & 6303 w/field Flattener

19 Focus A few microns here and there

20 Focus Establish a Baseline

21 Focus Thermal Effects on Focal Plane FOCUSER POSTION TEMPERATURE (CELCIUS) 3 Hour Temperature Difference = 1.9º C Focuser Movement = 351 Microns Critical Focus Zone = 220 Microns Celestron C9.25, Optec TCF-S Focuser, FocusMax & ST10XME

22 Focus Off Target Focusing in Action Perform Focus Run Slew Telescope To To Focus Star and Center Search Catalog for for Suitable Focus Star Slew Telescope Back to to Target and Plate Solve Plate Solve Current Telescope Position

23 Tracking We all need a gentle nudge

24 Mount Performance Cure for Common Problems Periodic Polar Alignment Error

25 Mount Performance Polar Alignment Error 30 Arc-Seconds 20 Arc-Seconds POLAR ALIGNMENT ERROR: 30

26 Mount Performance Periodic Error 30 Arc-Seconds 20 Arc-Seconds PEAK-TO-PEAK PE ERROR: 9

27 Mount Performance Unguided Performance 30 Arc-Seconds 20 Arc-Seconds PE ERROR: 9 PA ERROR: 30

28 Mount Performance Polar Alignment Correction 30 Arc-Seconds 20 Arc-Seconds POLAR ALIGNMENT ERROR:

29 Mount Performance Periodic Error Correction 30 Arc-Seconds 20 Arc-Seconds PEAK-TO-PEAK ERROR: 9

30 Mount Performance Periodic Error Correction 30 Arc-Seconds 20 Arc-Seconds PEAK-TO-PEAK ERROR: 1

31 Mount Performance Unguided Performance 30 Arc-Seconds 20 Arc-Seconds PE ERROR: 1 PA ERROR: 0.3

32 Auto Guiding Avoid Short Guide Exposures RMS ARC-SECONDS OF ERRER GUIDE EXPOSURE DURATION IN SECONDS RMS Error (arc-sec) FWHM Star FWHM Star

33 Auto-Guiding Challenges of Long Guide Exposures 5 5 Second Second Guide Guide Exposure Exposure Correction Correction Periodic Errors Periodic Errors Polar Drift Polar Drift Wind and Vibrations Wind and Vibrations Flexure / Draging Flexure / Draging Cosmic Ray Hit Cosmic Ray Hit Correction Correction In In Five Seconds a Lot Can Happen!

34 Auto-Guiding Eliminating Other Sources of Tracking Error VIBRATION MANAGEMENT FLEXURE BALANCE CABLE MANAGEMENT

35 Auto-Guiding Software Settings MOUNT LIMIT: 1.0 MAX ERROR: 0.3 MOUNT LIMIT: 1.0 MAX ERROR: 1.0 MOUNT LIMIT: 0.6 MAX ERROR: 1.0 MOUNT LIMIT: 0.6 MAX ERROR: 0.6

36 Imaging Now lets have some fun

37 Imaging Results Excellent Performance FWHM: 1.86

38 Imaging Results Poor Performance FWHM: 2.73

39 Imaging Results Excellent Performance FWHM: 1.86

40 Imaging Results Poor Performance FWHM: 2.73

41 Imaging Results Bad Data FWHM: 1.86 FWHM: 2.73

42 High Octane Imaging

43 Performance Checklist 1. Check for Flexure 2. Balance Your System 3. Polar Align Your Mount 4. Perform Periodic Error Correction 5. Collimate Your Telescope 6. Determine Imaging Conditions 7. Optimize Guider Settings 8. Carefully Plan Target Location 9. Image, Focus, Dither, Repeat 10. Analyze your Results

44 Image Acquisition Best Practices Richard A. Bennion Ewell Observatory