First Steps In Astrophotography

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First Steps In Astrophotography
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First Steps In Astrophotography

• Cameras and what they can do
• Short exposure imaging
• Long exposure imaging
• Processing
• Some tricks

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Cameras (and what they can do)

• Camera types
• Strengths and limitations of camera types
• Best subjects for camera types

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Camera Types

• Digital or Film
• Simple point shoot
• More complex Point shoot
• Single Lens Reflex cameras
• Webcams
• CCD Cameras

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An (Important!) Aside!

• Start with what youve got
• Get a camera which isnt just for astronomy
• Get a tripod

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Digital or Film

• Film bit old hat but still good for some
  subjects
• Digital rapidly improving format with lots of
  variations

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Film

• Good cameras are very cheap on e-bay
• Film processing takes time
• High Dynamic Range (about 16-20 bits)
• Large sensor (35mm)
• 35mm film is equivalent to about 20 M Pixels
• Further processing requires scanning

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Digital

• Prices for high end cameras reducing
  quickly.Cheap cameras arent really coming down
  in price (just increasing pixel count)
• Instant results
• Limited dynamic range (8 to 14 bits)
• Small sensors (typically 10mm across)
• Easy digital enhancement and stacking

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Simple Point Shoot
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Simple Point Shoot

• ?Auto Exposure only
• ? Auto Focus only
• ? Small Sensor and dynamic range
• ?Nearly always have a live view on LCD screen
  (WYSIWYG)
• ?Light and cheap (50 up)
• ? Probably have one already!

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More complex Point Shoot
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More complex Point Shoot

• ? Exposure Control
• ? Probably no focus control
• ? Up to APS (26mm) sized sensor
• ? Limited Dynamic Range (8 bit jpg files)
• Live View
• ? Fixed Lens
• ? Has a Filter Ring
• ? Becoming bulky and more expensive. 150

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Digital SLR
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Digital SLR

• ? Pricey Typically 400 with lens but good 2nd
  hand market
• ? Full exposure and focus control
• ? APS or 35mm sensor
• ? 12 or 14 bit dynamic range (Raw file)
• ? No Live view except on most recent models
• ? Removable lens so can attach to telescope

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Webcams
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Webcams

• ? Take a video stream that can be stacked into a
  single image
• ? Dead cheap (30 - 60)
• ? Very small sensor
• ? Limited to bright subjects
• ? CCD Type best (ToUcam, SPC 900NC)
• ? Cheap adaptor connects to telescope

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CCD Camera
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CCD Camera

• ? 400 up (and up..) Good 2nd hand deals
• ? Cheap T Adaptor to connect to scope
• ? Needs capture software (maybe bundled)
• ? Low noise
• ? High sensitivity and dynamic range
• ? Specialised astro gear

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What can they do?

• Daytime pictures (Sunrise/set, halos, sundogs,
  etc)
• Constellation and wide field
• Moon
• Planets
• Long exposure telescope imaging

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Daytime Pictures
Auto Exposure Point Shoot Good. Convenient to carry for the unexpected
Manual Exposure Point Shoot Very Good. Allows bracketing of exposure
Digital SLR Very Good
Webcam No
CCD Camera No
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Moon
Auto Exposure Point Shoot Good Using Afocal method
Manual Exposure Point Shoot Potentially Very Good if coupled using filter ring
Digital SLR Very Good if using telephoto lens or scope
Webcam Excellent through scope Small field of view
CCD Camera OK but usually too sensitive
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Planets
Auto Exposure Point Shoot Planet too small for reliable results
Manual Exposure Point Shoot Planet too small for reliable results
Digital SLR Possible using eyepiece projection but not good
Webcam Excellent through scope Can get very good detail
CCD Camera Too sensitive and planet too small
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Constellation Wide Field
Auto Exposure Point Shoot Poor. Usually limited to short exposures
Manual Exposure Point Shoot OK if 10 to 30 second exposure allowed
Digital SLR Good if undriven, very good if driven
Webcam No
CCD Camera Very Good if matched with T SLR lens
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Long Exposure Telescope Imaging
Auto Exposure Point Shoot No
Manual Exposure Point Shoot No
Digital SLR Very Good
Webcam No
CCD Camera Excellent
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Daytime exposures (with normal lens)

• Views and phenomena
• Sunrises Sunsets
• Moon
• Eclipses
• Tripod a good idea
• Bracket exposures

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Moon and Venus 2008/01/05 0730 Canon
300D 55mm 1/10s F/5.6 800ISO Tripod
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Partial Lunar Eclipse 2006/09/08 2100 BST Canon
300D 400mm 1/160s F/4.5 800ISO Tripod
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Noctilucent Clouds 2006/07/14 2244 BST Canon
300D 27mm 2.5s f/8 800ISO Tripod
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Moon 22 Halo 2007/01/05 2207 Canon 300D 22mm
10s f/5.6 800ISO Tripod
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Moon and Venus 2004/01/24 1744 Minolta Dimage-X
17mm Auto-exposure f/3.6 200ISO Wedged
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Short Exposure Imaging with a Telescope

• Moon and Planets
• Sun with solar filter
• Need to provide high magnification for planets
  and crater detail
• Use eyepiece projection and afocal imaging

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Afocal Imaging

• Point camera with lens through telescope
  eyepiece!

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Lots of vignetting and need to be careful with
focus. Starts like this
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But careful composition and focus gets you this
with an afocal DSLR
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Or this with a simple point shoot camera
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Or this with a camera phone (not mine)
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Improving Afocal images

• PVC tube over the eyepiece
• Camera attachment

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Improving Afocal images

• PVC tube over the eyepiece
• Camera attachment
• Filter ring attachment

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Webcam Imaging

• Best way for planets
• Attach to scope with 1¼ inch adaptor
• Essential to replace IR filter

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Webcam Imaging

• Need a computer!
• Use Webcam software to record about 10s AVI
• Use Registax to stack the AVI
• http//registax.astronomy.net
• Fiddle with Wavelets to bring out detail
• Registax Demo

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Constellation and Wide Field

• Need a camera which allows 10 to 30s exposures
• Need a tripod
• Lens of about 50mm (35mm equivalent)
• Stacking software (DeepSky Stacker)

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Trailing

• The Earth rotates about its axis every 24 hours
• The stars appear to rise in the East and set in
  the West
• The amount of motion detected on the sensor is
  proportional to the magnification and the
  duration of the exposure

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Trailing Formula

• Trail Length FETcos(D)/ Pixel size
• where
• F Focal length of lens/scope (mm)
• E Exposure length (Sec)
• T 2?/86400
• D Declination of the star

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Star Trail Lengths on Canon 300DPixel size 7.1
microns
Focal Length Exposure Declination Trail Length
55mm 30s 0 17 pixels
24mm 30s 0 7 pixels
55mm 10s 0 5 pixels
55mm 30s 60 8 pixels
24mm 10s 60 1.2pixels
400mm 10s 0 123 pixels
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Orion 10s _at_ 35mm fl
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Closeup of the Belt Stars
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Tracking the Stars

• Piggy-back on a telescope

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Tracking the Stars

• Piggy-back on a telescope
• Dedicated Camera tracker

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Tracking the Stars

• Piggy-back on a telescope
• Dedicated Camera tracker
• Barn Door Mount

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Long Exposures with a Telescope

• Need
• SLR or CCD camera (prime focus)
• Coupling between camera and telescope
• A way to take pictures
• Good solid driven mount
• Way to focus accurately

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Coupling to Telescope

• Coupling via T mount and T-eyepiece adaptor
  Nosepiece
• Fully Screw-in system more robust but less
  flexible (e.g. SCT coupling)
• Focal Reducer can be used to widen field of view

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Taking Pictures with Digital SLR
Stand Alone Computer Control
You control the exposures directly Set up a sequence and let the computer do the exposures
Feedback is through the LCD screen Can display first exposures to make sure theyre right
Images stored in the camera memory card Can save in the camera or download to computer
Needs lots of batteries but can be done anywhere Need power supply for the computer
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Stand-Alone DSLR shooting

• Need remote shutter release (can be wireless!) to
  avoid shake (15)
• Set shutter speed to longest available if no
  bulb
• Set Mirror lockup if available
• Set resolution to RAW or best available
• Need lots of room on the memory card

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DSLR Remote Control H/W

• USB cable for control and download
• Probably need separate cable for bulb, about
  15 for a serial cable
• http//www.astronomiser.co.uk/

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DSLR Remote Control S/W

• Remote control using camera software or dedicated
  astro-sw, e.g.
• DSLR Focus (25)
• http//www.dslrfocus.com/
• DSLR Shutter (Free)
• http//www.stark-labs.com/DSLR_Shutter.html

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Good Solid Driven Mount

• Needs to be solid enough for the telescope plus
  the camera
• Need to get the balance right and may need more
  counterweight
• Longest exposure dependent on polar alignment
  (Field Rotation)
• Alt-Az OK for short exposures. Automated stacking
  takes care of field rotation

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Accurate Focus

• Remote control software has focus mode
• Use bright star for focussing
• Live View cameras make this easy (zoom)
• Hartmann Mask / Diffraction Spikes

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Processing

• Cant put back what wasnt there!
• Stacking to increase Signal to Noise Ratio
• Aligning to minimise tracking and field rotation
  issues
• Post-processing to enhance the signal

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Stacking

• Adds (or averages) a number of images
• Produces in increase in S/N ratio
• Makes the image smoother
• Mimics the effect of a longer exposure
  ExposureEffective?Num exposuresExposure
• Short exposures reduce
• Tracking errors
• Lost Exposures because of cloud or satellites

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Aligning

• Makes sure each image aligns with the others for
  stacking
• Manual 1 star alignment for tracking
• 2 star alignment for tracking and rotation
• Automatic star matching
• Correlation (Registax)

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Aligning Stacking Software

• Registax (Free)
• http//registax.astronomy.net
• DeepSky Stacker (Free)
• http//deepskystacker.free.fr/english/index.html
• IRIS (Free but very complex to use)
• http//www.astrosurf.com/buil/us/iris/iris.htm
• Images Plus (200)
• Astroart (120)
• MaximDL (expensive but best 459)

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Post-Processing

• Photoshop (in its various guises)
• Paintshop-Pro
• Images Plus, Maxim Astroart have some nice
  features (DDP FFT filters)

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Photoshop

• Various versions
• CS3 (hugely expensive, student version)
• Elements (60) but sometimes free with equipment
• Various older versions (typically 8 bit)

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Photoshop Manipulation

• Levels
• Curves
• Sharpening filters
• Noise / blur filters
• Layers and masks

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Blurred layer to remove gradients

• Duplicate as new layer
• Use DustScratches to remove stars
• Change mode to Difference

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Wash Layer to Increase Colour

• Duplicate image as a layer.Select layer
• Filter Median and Gaussian Blur
• Increase Saturation
• Change mode to Color (sic)

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Layer Masks to Increase Range

• Duplicate image
• Manipulate with curves, etc
• Layer on original (ctrl-A,ctrl-C and ctrl-V)
• Create a mask, select (alt click) and ctrl-V
• Gaussian blur the mask (10 pixels)
• Select the layer 1 image
• Merge down when happy

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Buying Second Hand

• Active upgrading so not just throwaways
• http//www.astrobuysell.com/uk
• Very active site (15 listings per day)
• http//www.astronomy-uk.co.uk/
• Less busy but all good stuff
• E-bay
• Some gems but 99 tat
• American sites for the adventurous

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Things Ive Left Out!!

• DSLR H-Alpha response and modification
• Bias, Darks Flats
• Polar Alignment
• Guiding
• Motorised focussing
• CCD imaging
• And lots more