Polaroid ST-8E, ST-9E, ST-7E manual Flat Fielding Track and Accumulate Images

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Section 5 - Advanced Imaging Techniques

functions except when you are in Full Frame Focus Mode. It will then automatically switch to Low Resolution Mode. If you further select Planet Mode for focusing, the camera will switch back to High Resolution on the selected box area. The small pixel size, is best for critical focusing. Planet mode will result in fast digitization and download times since only a small portion of the frame is read out.

In general, you should pick a binning mode that yields stars with two to three pixels full width at half maximum. This is easily measured by using the crosshairs to determine the peak brightness of a relatively bright star, and determining the number of pixels between the 50% values on either side of the peak. More than 3 pixels per stellar halfwidth merely wastes sensitivity without improved resolution.

5.7.Flat Fielding Track and Accumulate Images

This section gives the step by step procedure for flat field correcting images taken using the Track and Accumulate command.

Flat field correcting images allow the user to remove the effects of CCD response non- uniformity (typically less than a few percent) and optical vignetting which for some optical systems can be as much as a 50% effect from center to edge. The CCDOPS software allows flat field correcting images using the Flat Field command, but some preparation must be made to use that command with Track and Accumulate images. Essentially you must prepare a special flat field correction image for Track and Accumulate images. This special preparation is necessary to have the same set of alignment and co-addition operations apply to the flat field file that have occurred in acquiring the Track and Accumulate image. In general, the following procedure should be followed when flat field correction of Track and Accumulate images is desired:

1.Take a normal flat field image using the Grab command. You can use the dusk sky or a neutral gray or white card held in front of the telescope. Try to adjust the illumination and/or exposure so that the build up of light in the image yields values that when co-added several times will not overflow 65,000 counts. The number of times the image will need to be co-added without overflowing is set by how many snapshots you intend to use in Track and Accumulate. A good goal is to try and attain a maximum level in the flat field image of 1,000 to 2,000 counts which will allow co-addition 32 times without overflow.

Note: You will have to take a new flat field image anytime you change the optical configuration of your telescope such as removing and replacing the optical head in the eyepiece holder.

2.Save the flat field image on your disk using the Save command. In the following discussions this flat field file will be referred to as FLAT.

3.Take your Track and Accumulate image using the Track and Accumulate command and save it on the disk using the Save command. In the following discussions this Track and Accumulate image file will be referred to as IMAGE.

4.Immediately after saving the IMAGE use the Save Track List command on the PC or activate the Track List window on the Mac and use the Save command to save the Track and Accumulate track list. The track list is a file that describes

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Contents Operating Manual Page Table of Contents Technique Introduction Road Map of the DocumentationQuick Tour Ccdops for Windows or Macintosh Ccdops SoftwareCCD Camera Page Introduction to CCD Cameras Cameras in GeneralHow CCD Detectors Work Camera Hardware Architecture Full Frame and Frame Transfer CCDsCCD System Block Diagram Cooling CCD Special RequirementsDark Frames Double Correlated Sampling ReadoutPixels vs. Film Grains Flat Field ImagesGuiding Electronic Imaging Black and White vs. Color Page At the Telescope with a CCD Camera Step by Step with a CCD CameraAttaching the Camera to the Telescope Establishing a Communications Link Focusing the CCD CameraCamera Back Focus Processing the Image Finding and Centering the ObjectTaking an Image Displaying the ImageCrosshairs Mode Photometry and Astrometry Advanced CapabilitiesSub-Frame Readout in Focus Autoguiding and Self Guiding Track and AccumulateColor Imaging Auto GrabAt the Telescope with a CCD Camera Camera Hardware Connecting the PowerConnecting to the Computer Connecting the Relay Port to the TelescopeUsing Mechanical Relays Push to Make Switch Modification Joystick Modification Modular Family of CCD CamerasSystem Features 20.6x sizeum Focal length cm Camera Hardware Connecting the older model CFW-6 filter wheel to the Camera Battery Operation Page Terrestrial Imaging Advanced Imaging TechniquesLunar and Planetary Imaging Deep Sky ImagingChanging the Camera Resolution Taking a Good Flat FieldBuilding a Library of Dark Frames Flat Fielding Track and Accumulate Images Tracking Functions Advanced Imaging Techniques Page Cooling Booster Accessories for your CCD CameraAO-7 and Lucy-Richardson Software Tri-color ImagingCamera Lens Adapters and Eyepiece Projection Focal ReducersImage Processing Software Third Party Products and ServicesSGS Self-Guided Spectrograph Windows SoftwareSbig Technical Support Common Problems Common Problems Common Problems Page Glossary STV Glossary Glossary Appendix a Connector ad Cables Appendix a Connector PinoutsSbig Tracking Interface Cable TIC-78 Figure A1 CCD Connector for TIC Mating Appendix C Maintenance Cleaning the CCD and the WindowRegenerating the Desiccant Page Technique Appendix C Capturing a Good Flat FieldPage Index IBM PC Separations
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