1. 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

2. 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

3. 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

4. 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).

5. Field of View examples for common telescopes

6. 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

7. 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

9. Imaging Chains

10. 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

11. Main challenges
Target Finding Stability/Tracking Focus Pollution Processing

12. 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.

13. 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.

14. Imaging settings
ISO (
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

15. Mod/Unmodded Bandwidth comparisons

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

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

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

19. 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

20. 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

21. 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

25. 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

26. Basic Photoshopped image

27. Useful software
Capture (backyardeos backyardnikon) (Astro Photography Tool) (Sharpcap) Mount control for skywatcher Processing Many many others! Planning/Pointing MaximDL, TheSky etc commercial