Webcam Astro-imaging Workshop

1
Webcam Astro-imaging Workshop

• Dave Dockery
• Steve Barkes

2
Session 1 Overview
Goal To help everyone learn to achieve better
images with their equipment.

• Why Webcam Astrophotography?
• How Do Digital Cameras Work?
• Camera Settings
• Drift Imaging vs. Tracking
• Focusing
• Basic Operation of K3CCDTools
• Exercise Lunar Imaging

3
Why Web Camera Astrophotography?

• Inexpensive alternative to astronomical CCDs
• QuickCam and Unconventional Imaging Astronomy
  Group (QCUIAG)
• Digital video format
• Video Captures (AVI files)
• Single frame capture
• Some support long exposure modification
• Imaging advantages
• Full color
• Immediate results
• Can take many images to get a few at moments of
  good seeing
• Can combine many images to enhance image features
  and reduce noise

4
How Do Digital Cameras Work?

• CCDs invented as a type of analog computer memory
  that can store any value in its range, not just
  0 or 1
• These capacitive cells are arranged in an array
  and accumulate a charge when struck by a photon
• The charges are transferred out of the array and
  digitized into picture elements (pixels)
• The number of charge cells in the array
  determines the maximum image resolution in pixels
  (typically 640 x 480)
• The resolution of the digitizer (8bit, 12bit,
  16bit, etc.) determines the number of shades each
  pixel can represent (typically 8 bit)
• Advantages
• Sensitivity and digital format
• Disadvantages
• Noise is caused when a cell charges due to energy
  from sources other than incoming photons
  (thermal, electrical, cosmic rays, etc.)
• Charge cells can leak into adjoining cells when
  fully saturated causing blooming

5
Camera Settings

• Frame resolution
• Nominally want to use max to get the most pixel
  information across the target. For smaller
  targets, you can sometimes use a sub-window to
  increase frame rate.
• Frame rate and video compression
• Lower frame rates mean less compression
• Cameras advertise 30 fps but this is at the cost
  of image quality
• Typically must image at 5-10 fps at highest
  resolution for best quality (limitation of USB
  bandwidth)
• AGC and manual gain settings
• Can use Automatic Gain Control (AGC) for lunar or
  solar imaging. The object must mostly fill the
  frame to get good levels.

6
Camera Settings (2)

• AGC and manual gain settings (cont.)
• Use manual gain to set proper level for small
  objects (e.g. planets)
• Also use manual gain control to minimize shutter
  time during poor seeing conditions
• Shutter speed vs. seeing conditions
• Short exposures will capture more brief moments
  of good seeing.
• The higher the gain, the faster the shutter speed
  that can be used for a given light level. This
  is limited by the acceptable level of noise.
  (Higher gain means higher noise and it varies by
  camera)
• White balance
• White balance is normally left in auto-mode or in
  the outdoor setting.
• Gamma
• Intensity linearity scaling factor that is
  normally left in the default position.
• Saturation
• Color intensity normally set midrange

7
What factors effect image quality?

• Observing conditions
• Magnification
• Aperture and optical quality of telescope
• CCD resolution, sensitivity, and noise
• Tracking (for longer exposures)
• Ambient temperature
• Image Processing

8
Drift Imaging vs.Tracking

• Drift imaging
• Does not require a telescope mount that tracks
  the apparent motion of the stars.
• Use a fixed mount pointed ahead of the object
  (moon) and record an AVI file as the object
  drifts through the field of view.
• Creates the effect of flying over the terrain.
• Disadvantage cant stack images
• Tracking
• Alt-az vs. equatorial mounts (how many?)
• Field rotation
• Alignment accuracy vs. magnification
• Polar drift alignment

9
The Subtle Art of Focusing

• Problem Air turbulence and diffraction can make
  an image inherently blurry no matter how well you
  focus. (Covington)
• Focusing Procedure using a Hartman mask
• Point to a bright star (overhead will minimize
  turbulence)
• Install Hartman mask
• Optimize camera sensitivity so that star is
  visible but not saturated.
• Collapse star pattern to a tight point by
  adjusting telescope focus
• When using a SCT, lock focus if possible
• Remove Hartman mask and point to the target
• Alternate Method
• Use a high contrast area of the Moon or a set of
  sunspots and focus for max sharpness in place of
  steps 2 4

10
Setup and Capture (So, how do I make this stuff
work?)

• Setup telescope (tracking is preferred but not
  required for bright objects)
• Install camera and Barlow lens (if applicable)
• Set desired camera resolution
• Set frame rate for minimum compression
• Set camera exposure and gain levels
• Focus using the focus procedure
• Frame the shot
• Collect Data (Lots)

11
Image Processing Introduction

• Image processing software for digital
  enhancements
• Levels histogram fill dynamic range
• Curves/Colors
• Detail enhancement spatial frequency algorithms
• Smoothing
• Sharpening
• Combining images
• Stacking
• Summing
• Save during each processing step
• Use compressed format to share (50Kb rule of
  thumb)

12
K3CCDTools Basic Functions - Steve

• Overview and history
• Basic features and settings
• Camera controls
• How to use the meter to set levels manually
• How to capture single images and video
• How to open and save files
• How to save BMP images from AVI files

13
Session One Exercise Lunar Imaging

1. Set up telescope, camera, and laptop outside (You
   can use a Barlow lens, if needed)
2. Turn on AGC, set max resolution, and 5 fps frame
   rate
3. Locate the Moon and then focus on a high contrast
   feature using the focusing procedure
4. Turn off tracking and position the telescope so
   that the moon drifts into the FOV.
5. Capture an AVI video called MoonDrift and save
   it in the My Videos folder
6. Turn on tracking and center the moon or an
   interesting feature in the FOV.
7. Turn off AGC and manually adjust the gain to 50
   then adjust the shutter speed to achieve 75 full
   scale on the level meter.

14
Session One Exercise (continued)

• Capture an AVI and save it as MoonTracking
• Capture several single images and save them as
  BMP files in the My Pictures folder.
• Homework
• Load the MoonFixed AVI into K3CCD Tools and look
  through the individual frames. Find several of
  the sharpest and save them as BMP images.
• Use your favorite image processing software to
  adjust the brightness, contrast, and sharpness of
  your best lunar BMP file and make sure to save it
  under a new name.

15
Resources

• Internet Links
• http//www.qcuiag.co.uk/ - QCUIAG Site
• http//www.pk3.org/Astro/ - Peter Katreniak
  K3CCDTools
• http//webcaddy.com.au/astro/adapter.htm - Mogg
  Adapters
• http//www.zianet.com/dave.dockery/AstroPhotos.htm
  - Daves site
• http//www.barkosoftware.com/index.html - Steves
  site
• Egroups
• QCUIAG_at_yahoogroups.com
• aslcnm_at_yahoogroups.com
• Books
• Astrophotography for the Amateur - Covington
• Splendors of the Universe - Dickinson

16
Webcam Astro-imaging WorkshopSession Two

• Dave Dockery
• Steve Barkes

17
Session 2 Overview
Goal To help everyone learn to achieve better
images with their equipment.

• Camera Settings
• Effects
• Focusing Review
• K3CCDTools Planetary Wizard Exercise
• Registax
• Demonstration Jupiter Imaging

18
Camera Settings

• Frame resolution
• Nominally want to use max to get the most pixel
  information across the target. For smaller
  targets, you can sometimes use a sub-window to
  increase frame rate.
• Frame rate and video compression
• Typically must image at 5-10 fps at highest
  resolution for best quality (limitation of USB
  bandwidth)
• AGC and manual gain settings
• Use manual gain to set proper level for small
  objects (e.g. planets)
• Also use manual gain control to minimize shutter
  time during poor seeing conditions
• Shutter speed vs. seeing conditions
• Short exposures will capture more brief moments
  of good seeing.
• The higher the gain, the faster the shutter speed
  that can be used for a given light level. This
  is limited by the acceptable level of noise.
  (Higher gain means higher noise and it varies by
  camera)

19
Effects

• Sky conditions - probably the biggest factor in
  our ability to image fine detail.
• Take advantage of good conditions watch the
  Clear Sky Clock
• Equipment aperture, telescope type, condition
  of optics, dirt on sensor, collimation, and
  thermal stabilization.
• Tracking - mount alignment accuracy vs.
  magnification
• Polar drift alignment
• Two Star Alignment (Alt-Az)
• Stacking - why stack images?
• Improved SNR
• Planetary rotation limit on stacking
• Jupiter 90 seconds max (.41 day period)
• Saturn 120 seconds or so, less critical (.44
  day period)
• Mars 180 seconds (1.03 day period)

20
The Subtle Art of Focusing

• Focusing Procedure using a Hartman mask
• Point to a bright star (overhead will minimize
  turbulence)
• Install Hartman mask
• Optimize camera sensitivity so that star is
  visible but not saturated.
• Collapse star pattern to a tight point by
  adjusting telescope focus
• When using a SCT, lock focus if possible
• Remove Hartman mask and point to the target

21
K3CCDTools Planetary Wizard Exercise - Steve