astrophotography with a side of raspberry pi

Rob Pettengill - AAS

Astrophotography With A Side Of Raspberry PiRob Pettengill (rcp@alumni.stanford.edu) Austin Astronomical Society 11 April 2014

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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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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

Rob Pettengill - AAS

Sensor Telescope Target MatchWhy 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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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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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

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

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

Rob Pettengill - AAS 9http://www.raspberrypi.org

http://beagleboard.org/Products/BeagleBone+Black

http://www.intel.com/content/www/us/en/do-it-yourself/edison.html

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

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 f f 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

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/

Rob Pettengill - AAS

Hang Me ’Til I’m DoneAstro RPi 2.0

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Rob Pettengill - AAS

Screw Me Up TightAstro RPi 3.0 Uses a T-ring as a nut to bolt mounting plate for camera to the extension tubes

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Rob Pettengill - AAS

Acquisition Software StackIOT 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

Rob Pettengill - AAS

SoftwareMy 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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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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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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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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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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Rob Pettengill - AAS

Drizzle - Stacking Of Under Sampled ImagesA 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

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7 stacked ISO 6400 30 sec, dark frames, & post

Rob Pettengill - AAS

Rob Pettengill - AAS

What's Next?

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• 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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