Capturing and Processing Deep Space Images Petros Pissias Eumetsat Astronomy Club 15/03/2018
Agenda Introduction Basic Equipment Preparation Acquisition Processing Quick demo Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 2
Agenda Introduction Basic Equipment Preparation Acquisition Processing Quick demo Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 3
Astrophotography AstroPhotography : recording light coming outside of our planet Astro star Photography Photo light Graphy drawing 2 basic types of astrophotography Deep Sky Dealing with objects outside our solar system Planetary Dealing with objects inside our solar system Moon(s), Planets Each type requires different equipment and techniques. We will focus on deep sky astrophotography Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 4
Agenda Introduction Basic Equipment Preparation Acquisition Processing Quick demo Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 5
Telescopes Usually fast newtonian reflectors, apochromatic refractors. Price, Performance, Handling Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 6
Cameras Astronomy Cameras split into 2 categories: deep space and planetary. Deep space cameras Large sensor (Regulated) Cooling CCD (or CMOS) Modified DSLRs (deprecated nowdays) Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 7
Target image Camera and optical system combination Focal length of the system: Telescope FL, Barlow (focal length multiplier) Magnification: related to camera pixel size and focal length FL Targets ~ 400-800mm (small FL) Wider shots (i.e. M42, M31) ~ >800mm (medium / large FL) High Magnification More demanding requirements on equipment > 1000mm Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 8
Basic Equipment Mono vs Bayer (colour) camera Mono advantages Better useful resolution Color advantages Simplicity (no filter wheel, re-focusing, ) Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 9
Basic Equipment Mount capable of tracking Equatorial vs alt/az Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 10
Setup in action Guide system is almost necessary Purpose : Tracks a star and sends corrections to the mount Mount are not perfect (Periodic error) Polar alignment will likely not be perfect Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 11
Agenda Introduction Basic Equipment Preparation Acquisition Processing Quick demo Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 12
Preparation Telescope / cameras / mount / filter wheel / laptop / cable connections, etc. Test everything beforehand to make sure everything works (software and hardware)! Choose a target relatively high (less atmosphere) Cool the telescope. Leave it out for some time (depending on tis size and in/out temperature) to reach the environment temperature. Collimation Align the optics of the telescope More frequently on Newtonians Light pollution is an issue Can have a dramatic effect Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 13
Agenda Introduction Basic Equipment Preparation Acquisition Processing Quick demo Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 14
Workflow Setup equipment (balance telescopes, align, ) Focus cameras (main camera and imaging camera) Find Target Start guiding Start taking images ----- Take flat frames (always needed) Take dark frames (if needed not always with regulated cooling) ----- Image(s) processing Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 15
Typical Setup - Target is framed - Camera is focused - Mount is tracking - Main camera taking images and saving to PC - Guide camera images are processed by an application on the PC which sends corrections to the mount Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 16
Acquisition Capturing Software APT Astro Photography Tool (all around tool) https://ideiki.com/astro/default.aspx Camera provided software Processing software is different Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 17
Focusing Focusing Not trivial Live view : center on star, play with focus Find star, take 4 second images with very high gain, several experiments Take test 2-3 images at normal duration (60-180 sec) Also Tools to help: Bahtinov mask, Motor focus, FWHM info Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 18
Pointing Targets are not always trivial to frame Especially when they are dim Goto can help Plate solving can help Software takes image Analyzes image to determine where the telescope is exactly pointed Corrects mount actual position Issues goto command to telescope to slew to target http://astropetros.eu/wp/?p=741 Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 19
Guiding One to rule them all PHD Guiding https://openphdguiding.org/ Other software available, but this just works Tweak mount control settings (guide pulse duration ) also on mount control software Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 20
Imaging We are ready to start taking images Exposure duration 60-180 seconds no hard rule, depending on the target Be careful not to overexpose bright targets (M42 core for example) Number of images The more the better Several amateurs take images on multiple nights Big difference depending on light pollution (with dark skies we need less images to produce the same result) Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 21
Dark frames and flat frames Dark frames To reduce noise Take several exposures of the same length as the images with no light reaching the sensor. to record noise and then remove it Flat frames To reduce optical defects Take several images of an evenly illuminated surface To record deviations from a perfectly illuminated image and take them into account Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 22
Dark frames Dark frames are absolutely essential To remove Dark current Although some sensors are reported to produce exceptionally low noise Read out noise Bias Dark frame stretched from my SBIG ST-2K Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 23
Flat frames Flat frames are absolutely essential to remove optical defects Difference in illumination on the FOV (also effects due to dust) Need to take also flat darks Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 24
Dark and flat frames Due to the extreme processing that we do, in order to bring out detail of the faint objects we recorded, these effects will be visible without dark and flat frames. Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 25
Agenda Introduction Basic Equipment Preparation Acquisition Processing Quick demo Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 26
Processing We have captured Lights Darks Flats Flat Darks Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 27
Processing We have captured (gigabytes of) data as image files. We need to process them. Calibration & Aligning (remove noise and prepare for stacking) Remove master dark frame (remove dark noise) from all images Master dark = combination of all dark frames Divide by master flat frame all images (equalize illumination) Master flat = combination of all flat frames Convert to colour (if using colour camera) Do star analysis and align (move + rotate) all images Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 28
Processing Stacking (reduce leftover noise, increase signal) Each picture now contains some leftover "noise after the calibration If the noise (thermal) is random, then combining many images will reduce it. "True" information increases more rapidly at the same point than random noise. Take the best of the pictures and combine (align and stack) them with specialized software. Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 29
Processing Stacking Reduce leftover noise after calibration Increase signal (i.e. virtually increase exposure time) Stacking parameters Median Mean Kappa-Sigma Post Stacking: Iterative histogram stretch Sharpening Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 30 https://www.flickr.com/photos/fyngyrz/3209392577
Processing Stacking Software Deep Sky Stacker http://deepskystacker.free.fr, also: IRIS (more hardcore specialized processing) PixInsight (very good reputation, commercial) http://www.astropix.com/html/i_astrop/software.html (comprehensive list from Jerry Lodriguss) I personally now just use Deep Sky Stacker (hands on session afterwards) Post Processing Any software able to read 16 bit per pixel images and do histogram manipulation. I personally use Nebulosity 2 http://www.starklabs.com/nebulosity.html Also nice sharpening and noise reduction features for the final touch Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 31
Processing Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 32
Processing Final steps Crop Save as 8 bit JPG Always keep your original stacked image (and raw files) for later re-processing [cloudy nights] Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 33
Thank You Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 34
Agenda Introduction Basic Equipment Preparation Acquisition Processing Quick demo Petros Pissias Eumetsat Astronomy Club 15/03/2018 Slide 35