Rob Pettengill gave a presentation on astrophotography using a Raspberry Pi. He discussed using low-cost computers like the Raspberry Pi and other single-board computers for applications in astronomy such as remote observing, telescope control, and camera control. He described building a system using a Raspberry Pi connected to a camera module to take astroimages. Key lessons included the importance of focus, aiming bright objects, and software for image acquisition, stacking, and processing. Future directions could include wireless connectivity and better support for cooled cameras.

1. Rob Pettengill - AAS
Astrophotography With A Side Of Raspberry Pi
Rob Pettengill (rcp@alumni.stanford.edu)
Austin Astronomical Society
11 April 2014
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2. Rob Pettengill - AAS
My Name Is Rob &
I Am Addicted To Astronomy
• I am not a professional
Astronomer
• Please do try this at home
• Follow your own
inspiration & needs
• Have fun
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3. Rob Pettengill - AAS
AGENDA
• Review Basic
Astrophotography
• Explore The Intersection Of
Internet Of Things &
Astronomy
!
1. Quick Context
• Astrophotography (Trade-Offs)
• Internet Of Things &
Raspberry Pi
2. What I Built
3. What I Learned Taking &
Processing Images
4. What's Next…
Christos Vasilas of Dash One
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1st afocal RPi Cam astro images

4. Rob Pettengill - AAS
Sensor
Telescope
Target
Match
Why not capture everything?
We must match Telescope & Sensor resolutions.
Example 89mm (3.5”) scope:
R = 4.56/D = 4.56/3.5 = 1.3 arc sec Dawes Limit
at prime focus 1.57º x 1.07º or 4348 x 2963 re or 12.9 MP
!
Dawes or Rayleigh Criterion gives resolution, you need 2X this to capture "the space
between” aka sampling theorem or 12.9 * 2 *2 = 52 MP!
!
For a 7” scope we need > 200 MP
!
With practical sensors, we can either maximize field of view or resolution but not both!
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5. Rob Pettengill - AAS
Trading Off
FOV and
Resolution
• Sensor Choice
• Extended Deep Sky Objects - Large sensors with
larger pixels
• Solar System - small sensors with smaller pixels
• Modify telescope Focal Length
• Panoramas (at n squared times the work)
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6. Sensor Size & Resolution Examples
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Sensor Size
mm
Resolution
Pixel Size
um
Pixel FOV
arc sec
Sensor FOV
arc min
RPi CM 3.67 x 2.74 2592 x
1944
1.4 0.224 9.79 x 7.3
Sony
NEX-5N
23.4 x 15.6
4592 x
3056
5.0 0.8 62.4 x 41.6
Starlight Ex
SX814C
12.5 x 10.0
3388 x
2712
3.69 0.59 33.3 x 26.7
Meade DSI
Pro III
10.2 x 8.3
1360 x
1024
6.45 1.03 27.2 x 22.1
Orion
Starshoot
5.77 x 4.3
2592 x
1944
2.2 0.352 15.4 x 11.5
Philips
SOC900NC
4.6 x 3.97 640 x 480 5.6 0.96 10.2 x 7.66
89mm Objective 1280mm FL
ScaleOfViewPrimeFocus=206.3/FLmm arc sec/µm, ResolutionLimitDawes=114/Dmm arc sec

7. Rob Pettengill - AAS
Astrophotography & FL
Camera (Rule of 500 / tripod, tracking
or piggyback mounts)
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Prime Focus Reducer
Shortened Focal Length
Barlow
Extended Focal Length
Eyepiece Projection
Extended Focal Length
Afocal / Digiscoping
Extended Focal Lengthdrawings from Televue

8. Rob Pettengill - AAS
Networked Computers so small and cheap
that they can be embedded in everything
!
Gartner - 26B by 2020
!
Astronomers have been pioneers
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Microcontrollers
Arduino...
Network Connected PCs
• RPi ARM $30
• Arduino Due $50
• BeagleBone Black ARM $50
• Intel MinnoBoard Atom $200
Graphic from mobilemarketingwatch.com

9. Rob Pettengill - AAS 9
http://www.raspberrypi.org
http://beagleboard.org/Products/BeagleBone+Black
http://www.intel.com/content/www/us/en/do-it-yourself/edison.html

10. Rob Pettengill - AAS
Internet Of Things And Astronomy
• Remote Observing downsized & updated.
• GoTo telescope control
• PushTo instrumentation and link to
planetarium software
• Automatic focusing.
• Guiding
• Camera control and enhancement.
• Plate solving.
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http://vaticanobservatory.org
http://simonbox.info/index.php/astronomy
http://www.recantha.co.uk/blog/?p=3615
http://astrobeano.blogspot.com/2014/01/instrumented-telescope-with-raspberry.html

11. Rob Pettengill - AAS
M a k i n g A s t ro p h o t o g r a p h y
A ff o rd a b l e P o r t a b l e & F l e x i b l e ?
DSLR (small screen/limited functionality)
alternatives require a computer.
• Largest component is the computer /
laptop
• Replace the computer with a small low
power wireless computer. ARM based
machines are powerful yet small and
low power.
• Replace the laptop display with a
wirelessly connected cell phone or
iPad. Better displays than many
laptops.
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Terry Belia astrotex.com

12. Rob Pettengill - AAS
R P i + C a m e r a M o d u l e +
Q u e s t a r C a m e r a A d a p t e r
C a n I t Wo r k ?
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https://www.flickr.com/photos/robpettengill/sets/72157635483690850/

13. Rob Pettengill - AAS
Hang Me ’Til I’m Done
Astro RPi 2.0
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14. Rob Pettengill - AAS
Screw Me Up Tight
Astro RPi 3.0
Uses a T-ring as a nut to bolt mounting plate for camera to the
extension tubes
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15. Rob Pettengill - AAS
Acquisition Software Stack
IOT based model - smart devices, using web based
interfaces on the network, to talk to personal devices.
• On the Raspberry Pi
• Camera Interface (raspicam)
• Web Server - translate camera control from Web
requests to raspicam, serve up images for aiming
and focusing
• Image storage on local SD card
• Wireless ad hoc WiFi network for communication
• On a smartphone or tablet
• Web browser with camera control interface
• Last still image
• Streaming video
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72 image Astro Raspberry Pi Lunar Panorama made with Hugin
Rob Pettengill - AAS

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BerryCam ready for Jupiter
imaging

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Jupiter Io & Europa 240 of 500 images stacked & sharpened

19. Rob Pettengill - AAS
Software
My environment Linux & OS X
Planning
• Stellarium
• AstroPlanner
Image acquisition:
Custom python web server on RPi front end to raspicam application. Motion JPEG & VLC streaming both
work.
Web browser or Berrycam app on iOS
Stacking & Preprocessing:
• Lynkeos - fast, powerful, easy to use (occasional crashes)
Nebulosity - powerful, robust, deep-sky oriented (also image acquisition)
Post processing
Photoshop
Hugin - amazing panorama tool
Gimp - powerful but not 16bit clean yet
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20. Rob Pettengill - AAS
Acquisition Lessons
• Good focus is essential! Bahtinov mask!
• It is hard to aim! Getting a bright planet in the field of view of a small sensor
imager is hard!
• Image latency from the imager to the display really matters in finding and
focusing.
• Use video streaming for aiming and focusing.
• Realtime cropping focusing aids matter.
• Speed of wireless link is important (802.11n or ac needed)
• Use RAW format if you can, but you can do without it for bright Solar System
objects.
• Cell phone camera imagers can give excellent Solar System results
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21. Rob Pettengill - AAS
Preprocessing Lessons
• Stacking “lucky images” gives amazing results.
• Automatic image grading helps, but is not enough
• Ease of reviewing & selecting images is essential
• Dark and Flat frames are essential for deep sky but
"not so much" for bright Solar System objects
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22. Rob Pettengill - AAS
Post Processing Lessons
Post processing balances art and science as you iteratively reveal the data in the
image in a pleasing realistic way.
• Deconvolve before stretching.
• Iteratively stretch (mid & dark points) with levels tool more controllable than
curves.
• Layers and masks are your friends, learn to use them well. Masks reduce
sharpening artifacts.
• Unsharp mask appears to give a sharper image, deconvolution really does.
• Iteratively sharpen and filter noise. Avoid and reduce sharpening artifacts.
• Finish off with color enhancement (gamma, saturation, vibrance) and curve tweaks
to enhance contrast.
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23. Rob Pettengill - AAS
Quick Resolution Check
• Calculate angular
pixel size
• Down-sample image
to reference
resolutions
• Up-sample reference
images to original
size
• Compare original to
reference images
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24. Rob Pettengill - AAS
Drizzle - Stacking Of Under Sampled Images
A Hubble example of a drizzle stack of 12 images from
Wikipedia shows recovery of under sampled data
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http://en.wikipedia.org/wiki/Drizzle_(image_processing)

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30sec ISO 6400 APS-C sensor
Rob Pettengill - AAS

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7 stacked ISO 6400 30 sec, dark frames, & post
Rob Pettengill - AAS

27. Rob Pettengill - AAS
What's Next?
!
• Lack of drivers for high quality cooled astrophotography imagers is a barrier
for now. A few already provide Intel Linux drivers and some ARM Linux (Point
Grey).
• High speed wireless network protocols will enable wireless astrophotography.
• Headless GoTo and PushTo telescopes with wireless connections to tablet &
smart phone apps.
• Embedded computers have a bright future in Astronomy, with smart phones
or tablets replacing laptops for user interfaces. IOT devices like Raspberry Pi
make it easier for amateurs to lead the way.
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