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Astrophotography with a side of Raspberry Pi
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Astrophotography with a side of Raspberry Pi


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A Practical Astronomy talk given to the April 11, 2014 meeting of the Austin Astronomical Society. Learn about the basics of low cost planetary astrophotography with the Raspberry Pi a credit card …

A Practical Astronomy talk given to the April 11, 2014 meeting of the Austin Astronomical Society. Learn about the basics of low cost planetary astrophotography with the Raspberry Pi a credit card sized Linux computer with a 5MP camera module that costs less than $70. Ultra small networked computers like the Raspberry Pi are being used by amateur astronomers in many ways. Details of the Astro RPi prime focus camera are described as well as sensor selection and optical and processing techniques to get the most out of your telescope images.
(Not sure why slideshare drops some slide images but the pdf download has them all.)

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  • 1. Rob Pettengill - AAS Astrophotography With A Side Of Raspberry Pi Rob Pettengill ( Austin Astronomical Society 11 April 2014 1
  • 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 2
  • 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 3 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! 4
  • 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) 5
  • 6. Sensor Size & Resolution Examples 6 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) 7 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 8 Microcontrollers Arduino... Network Connected PCs • RPi ARM $30 • Arduino Due $50 • BeagleBone Black ARM $50 • Intel MinnoBoard Atom $200 Graphic from
  • 9. Rob Pettengill - AAS 9
  • 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. 10
  • 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. 11 Terry Belia
  • 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 ? 12
  • 13. Rob Pettengill - AAS Hang Me ’Til I’m Done Astro RPi 2.0 13
  • 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 14
  • 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 15
  • 16. Rob Pettengill - AAS 16 72 image Astro Raspberry Pi Lunar Panorama made with Hugin Rob Pettengill - AAS
  • 17. Rob Pettengill - AAS 17 BerryCam ready for Jupiter imaging
  • 18. Rob Pettengill - AAS 18 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 19
  • 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 20
  • 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 21
  • 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. 22
  • 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 23
  • 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 24
  • 25. Rob Pettengill - AAS 25 30sec ISO 6400 APS-C sensor Rob Pettengill - AAS
  • 26. Rob Pettengill - AAS 26 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. 27