Astrophotography in the Classroom

For SEEC 2014 at NASA JSSDavid O’Dell, Anderson HS

Goals of this presentation

• Show you how to:• bring real astrophotography into your

classroom• use image processing software• use image measurement software• All this AND get the kids to enjoy it

Why take your curriculum this direction?

• Real science• Software is free• Learning curve is low• Student driven activity• Personal challenge (to you AND students!)• Transfer of skills to other activities

Deciding which type of Astrophotography will fit in your curriculum

• 2 types… each with their own set of hardware, price tag and challenges:• Deep Sky• Webcam

Deep Sky Astrophotography

• Most difficult, by far• Most expensive• Most rewarding (some say):– More objects out there than our solar system– “cooler looking” stuff like galaxies, colorful nebulae

Webcam Astrophotography• Super easy• Extremely cheap• Still very rewarding, just in different ways• … it’s what this presentation will cover!

You can do so much without a telescopeYou just need:

• Access to a few (or many) PC windows-based computers

• Permissions to install two small FREE software packages on those machines– AVI stack– http://www.avistack.de/download.html– Image J– http://rsbweb.nih.gov/ij/

• Sample videos and images (simply search online for .avi files)– http://www.skyimaging.com/astronomy-videos.php

…but much more with a telescope• All the previous items +• A single Windows XP or Win 7 laptop

– Usually from your school, or your personal one• Low Lux or comparable Web cam

– Usually less than $100– Philips SPC 900NC, or the 700NC– http://nightskyinfocus.com/equipment/philips-spc900nc00-webcam-for-ast

rophotography/• Sharp Cap web cam software

– FREE– http://www.sharpcap.co.uk/sharpcap/downloads

• 1.25 “ Web cam telescope eyepiece adapter– $15 to $30, search “1.25 web cam adapter” on EBAY

• … and of course… ANY size telescope

Why do we need the stuff we need

to do this?!?

Well… Think about what scientists collect…• Zoologists collect?• Animals!• Entomologists collect?• Bugs!• Philatelists collect?• Stamps!• Numismatics collect?• Coins!• Astronomers collect?????• LIGHT!

Astronomy specific issues

• Astrophotography environment is special– At night mostly– Large contrast • Night sky objects are bright compared to dark space

– Moist or cloudy air– Windy ground or upper altitude air turbulance– Objects difficult to find– Object difficult to focus– Objects appear to move as Earth rotates– Digital cameras generate waste heat, interference– Objects need long exposure times…

Deep Sky CCD chip cameras

• Specially designed:– stay “cool” to reduce hot pixels– Keep shutter open for long exposure times– Large CCD chip that is extremely sensitive

to very low light– Some only B&W, some color– Fit inside a telescope eyepiece tube– Software controlled capture settings

CCD Light sensitivity

• CCD will collect photons over a long period of time and produce a bright image from a dim object

• Long exposures are only possible if the telescope “tracks” the object

• If scope does not track object, the image is smeared across the CCD

Deep sky vs. Webcam imaging

• Solar system objects are considerably closer and appear larger compared to deep sky objects thousands of light years away… We don’t need the extreme sensitivity of a CCD.

• A planetary “webcam” is the best option for bright and relatively large solar system objects. Uses low power, less sensitive CMOS chip.

• Instead of long risky exposure times, the webcam takes hundreds of millisecond frames that are processed later using software

Settings to pay attention to:• Focus – webcams and CCD cameras are particularly sensitive to focus

shift!! Light travels a shorter distance than through an eyepiece, so focus is as if you had a 6 mm lens; very sensitive to any movement.

• Might need a focal reducer: Antares 1.25" 0.5x Focal Reducer• Gain – # photons that fall on that pixel are multiplied by a certain

amount; image might be brighter, but less accurate• Exposure – amount of time shutter is open, measured in seconds or

the number of frames you record

Taking a set of “Darks”

• Cameras all leak voltage out of the image chip• This leakage occurs in a predictable pattern• A long exposure image with the lens cap ON is taken and

the hot pixels are mapped and removed by software

The basic astrophotography process:

1. Setup scopes, cameras and computer; let cameras settle for 5 minutes to get used to the ambient temperature

2. Take a set of darks3. Find object and focus using eyes4. Place camera in eyepiece, reposition and focus using camera /

computer5. Choose settings and record video (using Sharp Cap)6. Do not walk nearby or touch scope

while imaging7. Save file for processing later

Onto the processing… process

1.Frame selection2.Alignment3.Stacking4.Post processing5.Scientific Measurement

& Comparison

Using AVI

stack

Using Image J

The following process is to “get the job done”. For specialized tweaks,

please read the AVI Stack manual

http://www.avistack.de/downloads/AviStack2_eng.pdf

Loading a file into AVI Stack• Open .avi movie file

from your webcam into AVI stack• Highlight file• Click PROCESS FILE• Frames will be counted

At any point you can make changes

• Each segment of the process is compartmentalized

• Simply click on a green folder in the Parameters and Settings window

• Make the changes and move on

Frame Selection – my #1 tip

• More frames doesn’t mean a better image.• Remember, pixels are the carriers of visual

information. Too much might be over kill.• You will NEVER need all the frames of video• For most webcam images of the moon and

planets, you’ll need no more than 500 frames; and only end up selecting around 200 of those to process.

Frame Selection• Using the video slider,

scroll through the frames and find ones that have problems such as dust, blur, birds, shakes and wild changes of position

• On frame selection panel, highlight, then ‘X’ them out in bulk using ‘shift’ key or one by one

• Click OK

Frame Alignment Parameters• Using frame selector

slider, scroll to the clearest frame

• Select “planet”, or “surface” for close-up lunar surfaces

• Adjust “area radius”• Left click to place 1st

alignment box, right click for 2nd box.

• Boxes should be on top of unique features

• Click OK

Alignment Deviation – the one graph you get to play with

• Too much deviation is bad.

• You want to reduce the number of frames used that have large alignment deviation from the previous frame

Reducing Deviated frames• Click and drag the

top axes of the top graph and pull the red line down, this will be the new cutoff.

• Frames that deviate too far (over 4 pixels in this example) will not be stacked

• Click OK

Framed Aligned Movie• This is where the

software first shows its true power

• Using the movie slider, scroll through the frames

• You’ll see that the image doesn’t move very much at all now

• Click OK

ROI (Region of Interest) Selection• Simply drag a

selection box around the part of the image you want to stack

• Click OK

Initial Stack Reference Point settings for most images• Used to help stacking

and quality management process

• Minimum distance below 18 is not recommended

• Structure threshold around 70 recommended

• Lower cut off 0• Upper cut off 1• Tweaking these is

most often used only with extremely noisy images

Quality Analysis

• Some frames contain better, sharper information in certain parts MORE than other frames.

• AVI stack can break up each frame into areas and make a quality judgment for use in the stacking process

Quality Analysis settings for most images• Standard quality

method selected• Noise reduction is

suggested to be 1 unless you have extremely noisy

• Quality area set to above 50, default is 84.

• Click OK

Frame quality diagram• Shows a

quality vs. frame curve.

• The highest quality frames will be first in the sorted list

Quality sorted movie

• Simply scroll through the frames of the movie and you will see that sharper, high quality frames are first

• Low quality frames are last• Click OK

Final reference point alignment• Area radius around 25

• Search radius is best left automatic since this is calculated

• Quality cut off IS EXTREMELY IMPORTANT, choose to use first 30% of frames, or, use a specific number of frames by checking frame cut off

Frame Stacking• Screen will be

black, this is normal

• Click OK and watch the quality sections appear and stack piece by piece

• Some errors and dust specks might disappear!

Why Stack? The picture looks pretty good!

• You might have one single color image, however, it may not be enough pixels to make a truly magazine quality image

• You need LOTS and LOTS of combined images

• You need to STACK your images

Image Stacking – No Pixel Left Behind!

• Image stacking is a process where many frames of an image are placed on top of one another to increase the amount of pixel coverage

StackingExamples

Saving stacked image

• Choose the filename and directory you want to save to

• Click Save• You’re not done…

Post-Processing• Click the “post processing”

green folder• Wavelets, Levels,

Histogram and Clipping• Only Wavelets and Levels

are needed

Wavelets and Levels

• Adjust the wavelet sliders to sharpen your image or bring out certain surface details

• Top slider of a layer is the amount, bottom slider is amplitude

• Levels are easily adjusted to help control color contrast

Saving Post Processed image

• You will need to save this image as a new image

• AVI stack will automatically append the suffix _pp to the end of your filename

Great results either way, ready for scientific measurement!!

• Stacked ONLY • After post-processing

Basic measurement with Image J

• Image J only recognizes pixel dimensions, it has no idea the scale of any image

• First priority is to set some sort of scale of pixels to km or miles

• Easily done as long as the object has a known diameter

• Diameters of all planets, moons, volcanoes and major craters are on Google

How to set scale using a known distance

• Open image into Image J

• Using the line segment tool, draw a diameter line across the object

• Click ANALYZE > SET SCALE

• Type in the ‘known distance’

• Set units• Click OK

Choosing measurements to display• Click ANALYZE > SET

MEASUREMENTS• Check fields you

want to display and measure

• Click OK

Making measurements• Using the line segment,

freehand, or ellipse tool find a feature and draw over or around it

• Click ANALYZE > MEASURE

• A new results window will appear

• Repeat process and new measurements will appear in window

Comparison of Scale• Astronomical measurements

are usually on extreme scales

• It helps students comprehend scale by comparing the measured object’s size to something familiar on Earth, such as:

• Distance to a nearby city• How many New England

states could fit into…• Or simply, number of Earth

diameters

Any Questions, Contact me!

• David O’Dell• Anderson High School, Austin TX• david.odell@austinisd.org