Deep Sky Imaging with Telescope and DSLR Tonight 7PM 16 October 2017 Stardome, Auckland Deep Sky Imaging with Telescope and DSLR Shaun Fletcher Auckland Astronomical Society

What is this talk about? Prime focus imaging with a tracking equatorial mounted telescope and DSLR Canon specific but generally applicable Getting to your first ‘wow’ image Understanding the challenges Doing it on a budget

What is this talk not about? Wide field/Milky way astrophotography Eyepiece projection CCD/CMOS dedicated cameras and software Producing professional images Advanced post production Spending a lot of money

What kind of things can I image? Examples of objects Nebulae - Bright nebulae. Emission nebulae. Reflection nebulae. Dark nebulae. Planetary nebulae. Galaxies. Single large Galaxies, galaxy group fields. Star clusters. Open clusters. Globular clusters. Compare fields of view Slow Telescope (SCT). Fast Telescope (Newtonian). Long Lens. Types of telescopes for different purposes No fixed answer.. But types have natural strengths. SCT Nebulae and Galaxies, Globular Clusters. Newtonian Larger Nebula and Galaxies, Clusters, Diffuse Nebulae (Orion). Camera lens (or mosaic) large fields containing multiple or diffuse objects and clusters (Pleiades).

Field of View examples for common telescopes

The theory (there will be no exam) Stacking/integration – what is it and how does it work Read noise Bias Hot/Cold Pixels In the simplest terms, this is averaging out a set of images to prioritise the real image over noise sources. Flat Fields A program like DeepSkyStacker(or MaxinDL or PixInsight) automates this in several steps: Filters Light Pollution Alignment.. The image is aligned across all frames, to remove tracking and movement. Narrowbands Analysis.. The sequence is analysed to rank the images by quality. Some may be discarded if they are poor. Prime focus What does that mean, and where is it? Integration/stacking.. The images are mathematically combined in some way to increase the signal to noise ratio. DSLR CMOS Calibration What is it, what about CCD, is CMOS inferior? RGB Matrix, One shot colour Removal of the following kinds of noise Small pixels, best for? Sky/random/photon noise Camera noise due to heat/Dark current

Equipment used Telescope OTA (almost any). Adapters Mount Camera. SCT/RC Newtonian Refractors Adapters T Mount Nosepiece 2 or 1.25 Reducers Barlows Mount Any equatorial Camera. Canon 450D+ Other brands Remote USB capture and control minimum Computer Laptop, win 7-10, multiple USB Accessories USB-mount cable Power supplies USB camera cable (wifi?) Gamepad Polarscope/polemaster

Imaging Chains

Software used Setup (Polar alignment assist) Frame, focus, Capture Alignmaster BackyardEOS Sharpcap Many Alternatives (MaximDL, AstroPhotographyTool, Canon EOS Utility) PoleMaster Stacking/enhancement Telescope Control DeepSkyStacker ASCOM MaximDL EQMOD (Skywatcher) PixInsight Stellarium/StellariumScope Image processing Proprietary/other AstroTortilla Photoshop Sequence Generator Pro Alternatives gimp, any image processing program EQMosaic

Main challenges Target Finding Stability/Tracking Focus Pollution Processing

Capture Process - Planning What is in the sky Stellarium/carte du ciel/thesky etc. many charts online. What interesting stuff is happening when Deep Sky objects do not change in our timescale! Comets, Asteroids, Pluto etc do. Variable stars do. Altitude Simply the higher the better.. Better to image at 2am at 60degrees than 11pm 35degrees. Also the later the night goes on the less heat noise, pollution and traffic etc. Multiple sessions Images can be combined over many sessions, even over seasons, and mosaics etc can be built up over time.

Setup/pre-capture Imaging chains SCT/Newtonian/Refractor Mounts - Polar alignment and balancing The single most important part of the process is polar alignment. Balancing helps keep tracking clean and avoids strain on motors Computer setup/ Connectivity Approximate focus Find a bright star or even planet or moon, use live view, try to record focus point if possible. Obtain target and preview Can be challenging dependent on your equipment, mount accuracy. Frustrating at times use widest view possible and rely on your finder, Good finder setup useful Focus Find a mid brightness star, use live-view and software tool to show FWHM. Depending on collimation and flatness of frame, focus on a star half way out from mid to get best across whole frame Recheck/Refine focus If setup is stable and focus remote this can be pretty easy. If not can be very frustrating, but worth spending some time. Also recheck focus between every few captures (assuming you are not posh enough to have an automated focuser) Guiding Off-Axis. Guidescope. PHD. MaximDL. Calibration. Equipment/cameras.

Imaging settings ISO (http://dslr-astrophotography.com/iso-dslr-astrophotography/) Highest ISO that works without maxing out the dynamic range or swamping post/ADC noise is best. Suggested example typically 800 on consumer camera, or 1600 with 6D level camera. Exposure times tracking and background, or blowouts Filters/mods LP filters, narrowband filters Calibrations Dark most vital, then flats. Bias of questionable value with DSLR but I use Dark taken occasionally. Length and ISO same. Flats taken if anything changes. ISO Same. Bias any time. Example of image set Show images

Mod/Unmodded Bandwidth comparisons

Examples of images direct from camera Unfiltered 450D 1600ISO 300Sec unfiltered 450D 1600ISO 30Sec unfiltered

Examples of images direct from camera Light pollution filters 450D 1600ISO 300Sec Astronomik CLS Filter 60D 6400ISO 240Sec Optolong CLS Filter

Examples of images direct from camera Narrowband Filters 450D 1600ISO 300Sec HA Filter 450D 1600ISO 300Sec OIII Filter

My Capture Process Preparation Set up imaging sequence. Capture Connect all equipment and start programs. Check camera on manual/bulb and RAW Point to initial focus star Use live-view mode to focus off centre Point to intended target If anything in frame bright enough check focus Set up imaging sequence. Name object Set filter name Set ISO and length Take preview image Capture Start up and calibrate guider if in use (longer than 30/60 seconds depending on tracking) Start capture sequence Watch at least first image result on screen Switch off/cover screen to reduce light spill. Retire to house and use VNC viewer to monitor progress (If you have the luxury!) Rinse and Repeat

Capture process – Calibrations Flats Camera on Manual/bulb Setsequence to darks Wait for twilight.. Mid blue sky Take as many as you have time for.. At least 5 Point scope fairly high Can keep for as long as temp not too different Set camera to AV Bias Set sequence for AV-Flats Often regarded as optional on DSLR Take many frames (50 or more) Set camera to bulb/manual Cannot use if anything changes in imaging chain, including filters Set bias sequence shutter (not length) to fastest shutter speed possible Darks Lots of frames, hundred or more. Set for each ISO/length Do once. Do at night, after finishing imaging usually Cover scope

Processing Stacking example dss screen and output Open deepskystacker Drag/drop or open light frames Calibration Drag/drop or open dark, flat, bias and choose right type Once done once can use resulting master frame tif! Register checked pictures Many settings, see screenshots and demo Register/stack may take some minutes Output to image folder. 32 bit tif Post adjustments and formats available in DSS for the brave example dss screen and output

Image processing/photoshop Convert tif to jpg. Do all enhancement before converting to 8 bit RGB alignment. Can be easier to make final tweaks here. Histogram. Endless scope to adjust curves and levels Noise reduction and sharpening. Light touch needed, again don’t try to render what is not there. Can be interesting to treat RGB channels as separate for this purpose as they are often very different in noise levels Overall visual tweaks. Brightness/contrast etc.. Just don’t go mad. Some nice astrophotography preset sets available

Basic Photoshopped image

Useful software Capture https://www.otelescope.com/ (backyardeos backyardnikon) http://www.ideiki.com/astro/Default.aspx (Astro Photography Tool) http://www.sharpcap.co.uk/sharpcap/downloads (Sharpcap) Mount control for skywatcher http://eq-mod.sourceforge.net/ http://www.alignmaster.de/ http://www.sharpcap.co.uk http://www.stark-labs.com/phdguiding.html Processing http://deepskystacker.free.fr/english/index.html https://pixinsight.com/ Many many others! Planning/Pointing http://www.stellarium.org/ https://sourceforge.net/projects/skychart/ MaximDL, TheSky etc commercial