Polaroid ST-7E manual Finding and Centering the Object, Taking an Image, Displaying the Image

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Section 3 - At the Telescope with a CCD Camera

the eyepiece barrel. The next time the CCD is used the eyepiece should be first inserted into the tube to the scribe mark, and the telescope visually focused and centered on the object. At f/6 the depth of focus is only 0.005 inch, so focus is critical. An adapter may be necessary to allow the eyepiece to be held at the proper focus position. SBIG sells extenders for this purpose.

3.5.Finding and Centering the Object

Once best focus is achieved, we suggest using "Dim" mode to help center objects. This mode gives a full field of view, but reduces resolution in order to increase the sensitivity, and digitization and download rate. If you have difficulty finding an object after obtaining good focus, check to be sure that the head is seated at best focus, then remove the head and insert a medium or low power eyepiece. Being careful not to adjust the focus knob on the telescope, slide the eyepiece in or out until the image appears in good focus. Then visually find and center the object, if it is visible to the eye. If not, use your setting circles carefully. Then, re-insert the CCD head and use FOCUS mode with an exposure time of about ten seconds, if it is dim. Center the object using the telescope hand controls.

Note: With a 10 second exposure, objects like M51 or the ring nebula are easily detected with modest amateur telescopes. The cores of most galactic NGC objects can also be seen.

3.6.Taking an Image

Take a CCD image of the object by selecting the Grab command and setting the exposure time. Start out with the Image size set to full and Auto Display and Auto contrast enabled. The camera will expose the CCD for the correct time, and digitize and download the image. One can also take a dark frame immediately before the light image using the Grab command.

Because the ST-7E/ST-8E/ST-9E have regulated temperature control, you may prefer to take and save separate dark images, building up a library at different temperatures and exposure times, and reusing them on successive nights. At the start it's probably easiest to just take the dark frames when you are taking the image. Later, as you get a feel for the types of exposures and setpoint temperatures you use, you may wish to build this library of dark frames.

3.7.Displaying the Image

The image can be displayed on the computer screen using the graphics capability of your PC. Auto contrast can be selected and the software will pick background and range values which are usually good for a broad range of images or the background and range values can be optimized manually to bring out the features of interest.

The image can also be displayed as a negative image, or can be displayed with smoothing to reduce the graininess. Once displayed, the image can be analyzed using crosshairs, or can be cropped or zoomed to suit your tastes.

3.8.Processing the Image

If not done already, images can be improved by subtracting off a dark frame of equal exposure. You will typically do this as part of the Grab command although it can also be done manually

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Contents Operating Manual Page Table of Contents Technique Road Map of the Documentation IntroductionQuick Tour Ccdops Software Ccdops for Windows or MacintoshCCD Camera Page Cameras in General Introduction to CCD CamerasHow CCD Detectors Work Full Frame and Frame Transfer CCDs Camera Hardware ArchitectureCCD System Block Diagram CCD Special Requirements CoolingDouble Correlated Sampling Readout Dark FramesFlat Field Images Pixels vs. Film GrainsGuiding Electronic Imaging Black and White vs. Color Page Step by Step with a CCD Camera At the Telescope with a CCD CameraAttaching the Camera to the Telescope Focusing the CCD Camera Establishing a Communications LinkCamera Back Focus Displaying the Image Finding and Centering the ObjectTaking an Image Processing the ImageAdvanced Capabilities Crosshairs Mode Photometry and AstrometrySub-Frame Readout in Focus Track and Accumulate Autoguiding and Self GuidingAuto Grab Color ImagingAt the Telescope with a CCD Camera Connecting the Relay Port to the Telescope Connecting the PowerConnecting to the Computer Camera HardwareUsing Mechanical Relays Push to Make Switch Modification Modular Family of CCD Cameras Joystick ModificationSystem Features 20.6x sizeum Focal length cm Camera Hardware Connecting the older model CFW-6 filter wheel to the Camera Battery Operation Page Deep Sky Imaging Advanced Imaging TechniquesLunar and Planetary Imaging Terrestrial ImagingTaking a Good Flat Field Changing the Camera ResolutionBuilding a Library of Dark Frames Flat Fielding Track and Accumulate Images Tracking Functions Advanced Imaging Techniques Page Accessories for your CCD Camera Cooling BoosterFocal Reducers Tri-color ImagingCamera Lens Adapters and Eyepiece Projection AO-7 and Lucy-Richardson SoftwareWindows Software Third Party Products and ServicesSGS Self-Guided Spectrograph Image Processing SoftwareSbig Technical Support Common Problems Common Problems Common Problems Page Glossary STV Glossary Glossary Appendix a Connector Pinouts Appendix a Connector ad CablesSbig Tracking Interface Cable TIC-78 Figure A1 CCD Connector for TIC Mating Cleaning the CCD and the Window Appendix C MaintenanceRegenerating the Desiccant Page Appendix C Capturing a Good Flat Field TechniquePage Index IBM PC Separations
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