Webcam Astro-imaging WorkshopWebcam Astro-imaging Workshop

Dave Dockery

&

Steve Barkes

Session 1 OverviewSession 1 Overview

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

Goal – To help everyone learn to achieve Goal – To help everyone learn to achieve better images with their equipment.better images with their equipment.

Why Web Camera Astrophotography?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

How Do Digital Cameras Work?How Do Digital Cameras Work? CCDs invented as a type of analog computer memory that can

store any value in it’s 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”

Camera SettingsCamera 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.

Camera Settings Camera Settings (2)(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

What factors effect image quality?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

• 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 – can’t stack images

• Tracking• Alt-az vs. equatorial mounts (how many?)

• Field rotation

• Alignment accuracy vs. magnification• Polar drift alignment

Drift Imaging vs.TrackingDrift Imaging vs.Tracking

Problem: Air turbulence and diffraction can make an image inherently blurry no matter how well you focus. (Covington)

Focusing Procedure using a Hartman mask:1. Point to a bright star (overhead will minimize turbulence)2. Install Hartman mask 3. Optimize camera sensitivity so that star is visible but not

saturated.4. Collapse star pattern to a tight point by adjusting

telescope focus5. When using a SCT, lock focus if possible6. Remove Hartman mask and point to the targetAlternate 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

The Subtle Art of Focusing

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)

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

Image Processing IntroductionImage 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)

K3CCDTools Basic Functions - SteveK3CCDTools 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

Session One Exercise – Lunar ImagingSession 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.

Session One Exercise (continued)Session One Exercise (continued)

8. Capture an AVI and save it as “MoonTracking”

9. Capture several single images and save them as BMP files in the My Pictures folder.

10. Homework:1. Load the MoonFixed AVI into K3CCD Tools and look through the

individual frames. Find several of the sharpest and save them as BMP images.

2. 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.

ResourcesResources 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 - Dave’s site– http://www.barkosoftware.com/index.html - Steve’s site

Egroups– QCUIAG@yahoogroups.com– aslcnm@yahoogroups.com

Books– Astrophotography for the Amateur - Covington– Splendors of the Universe - Dickinson

Webcam Astro-imaging WorkshopWebcam Astro-imaging WorkshopSession TwoSession Two

Dave Dockery

&

Steve Barkes

Session 2 OverviewSession 2 Overview• Camera Settings• Effects• Focusing Review• K3CCDTools Planetary Wizard Exercise• Registax• Demonstration – Jupiter Imaging

Goal – To help everyone learn to achieve Goal – To help everyone learn to achieve better images with their equipment.better images with their equipment.

Camera SettingsCamera 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)

EffectsEffects• 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)

Focusing Procedure using a Hartman mask:

1. Point to a bright star (overhead will minimize turbulence)

2. Install Hartman mask

3. Optimize camera sensitivity so that star is visible but not saturated.

4. Collapse star pattern to a tight point by adjusting telescope focus

5. When using a SCT, lock focus if possible

6. Remove Hartman mask and point to the target

The Subtle Art of Focusing

K3CCDTools Planetary Wizard Exercise - SteveK3CCDTools Planetary Wizard Exercise - Steve