JUST THE BASICS

1. Plan the objects to be imaged based on the field of view (FOV) yielded by the focal length of the optical system and the size of the CCD chip.

2. Polar align the scope or otherwise (if alt-az) set it up for accurate tracking. If no autoguider or manual guiding is used, then assure that well-tracked unguided exposures at least 15 seconds long can be made.

3. Hook up the camera to the controlling computer, turn it on, cool it down, and mount it to the focuser of the telescope so that the chip can be positioned at the primary focal plane. It is good 1) to assure that the entire chip is fully illuminated by the primary mirror (no vignetting), 2) to mount the camera to a swivel or a slide so that the camera view can be interchanged with an eyepiece view for object centering, 3) to have a large finder scope with center reticle well-collimated with the primary scope to allow quick finding and centering of objects, and 4) to have some sort of focusing aid (Hartmann or diffraction mask, focus mode non-ABG blooming, etc.); but NONE of these things are mandatory! They are handy and are highly desirable, but you can make dandy images struggling along without them at first!

4. Set the camera to the binning mode and other settings appropriate to the imaging plan.

5. Center a medium-bright star (3rd-7th magnitude, depending on the size of the scope) in the camera FOV, put the camera in focus mode (if available), and focus the star as best you can. Lock the camera/focuser into position and/or mark it for easy return.

6. Center the object to be imaged in the FOV and take test exposures to assure good tracking, focus, and framing. Determine the maximum exposure duration usable for the tracking and pixel saturation limitations. Cameras without anti-blooming will allow bright stars to bloom and this should be minimized as much as possible, but without sacrificing the usable exposure duration needed for acceptable signal-to-noise-ratio (SNR). If limited to very short exposures (less than 30 seconds), good SNR can still be achieved by acquiring and stacking numerous exposures.

7. Cover the camera's optical window so that NO light can reach the chip and take a dark frame the same exposure duration as your light (object) frames. Depending on your setup, either the camera itself, the bottom of the focuser, or the front end of the scope may be covered to achieve complete darkness. The acquisition software should allow the dark frame to be stored in a buffer so that it can be subtracted from light frames as you take them to allow you to really see what you are getting in your images.

8. If imaging a faint deep-sky object, take MANY MINUTES of total exposures so that a very good SNR image can be processed later. Take several dark frames over the course of the night so that these can be averaged later into a good master dark frame for high-quality processing.

9. If using a vignetted optical system or a telecompressed SCT (especially if used under less-than-very-dark skies), take flat-field images using a light box or a very evenly illuminated "surface", such as a smooth wall, a large posterboard, or a twilight sky. Flat-field frames are made with the scope looking into the dimly-lit light box or at the dimly illuminated "surface" and result in an image of the optical and CCD array itself. Make sure that flat-field frames are made with the camera in exactly the same focuser orientation and position as in the object frames. Flat-field images need only be a few seconds long, just long enough to raise the pixel values to about 20-50% of saturation. Take several so that they can later be averaged. Take several dark frames the same exposure duration as the flat-field frames so that they can later be averaged and used to calibrate the master flat-field frame.

10. If doing "true color" imaging, make sure to use an IR blocking filter for all color-filtered images. Take a few minutes' worth of exposures through each filter after taking the unfiltered (or IR blocker only) images, carefully checking the focus through each filter. If flat fielding is necessary don't forget to do it for each filter!

11. Use astronomical image-processing software to calibrate, stack, and otherwise process your raw CCD images to bring out the objects of interest (nebulae, star clusters, etc.) so that they can be seen in detail with appropriate brightness, contrast, range of grayscale, and (if applicable) color balance. Image processing and software experts such as Richard Berry, Bruce Johnston, Michael Newberry, Douglas George, and Christian Buil (and others) have all written full-range programs which may be capable of reading and manipulating the raw images from your camera.

12. The first step in processing is to calibrate the light frames. This means to remove unwanted signal and reduce noise factors in the object images and it is accomplished by subtracting a dark frame from the light frame and, if needed, dividing a mathematically normalized flat-field frame into the light frame (see subsection b. under the section called Processing Images). Before calibrating the light frames, create a good master dark frame by averaging several darks taken at the same exposure duration as the light frames. Save the master dark frame and use it to accomplish the dark subtraction. Similarly, create a good master flat-field frame by averaging several flat-lights and averaging several flat-darks, then subtracting the master flat-dark from the master flat-light.

13. After the images have been calibrated, short exposures of the same object can be stacked (averaged) to create, in effect, an image of longer total exposure duration and much higher SNR. Use your software to register/rotate the subexposures as necessary to assure that all objects in the images (stars, nebulae, etc.) stack exactly on top of themselves. Short subexposures often benefit greatly by being scaled linearly (all pixels in the array multiplied by a constant) before being stacked. Depending on how the software mathematically accomplishes the stacking, this will increase the number of grayscale levels in the object of interest. Save the calibrated stack as a FITS image.

14. If color-filtered images were made to produce a color composite image, calibrate and create each color stack. If a scaling factor is used during stacking, be sure to use the same scaling factor for all color stacks so that the subsequent color balancing process is not affected.

15. If the CCD pixels are not square, resample the images appropriately to correct the aspect ratio. Process the calibrated final unfiltered (white) image using linear and/or nonlinear scaling functions to bring out desired details, brightness, and contrast in the objects of interest. In addition, filtering functions may be used to soften and/or sharpen details in the image.

16. If color-filtered images were made, scale the stacked data to color-balance the RGB image sets in accordance with the relative RGB sensitivity of the chip/filter system. If CMY filters were used, convert the image data to RGB image sets using CMY color compositing software before color-balancing the RGB images. Neutralize the effects of foreground sky color (from light pollution, etc.) by normalizing the sky background pixels in the RGB images to the same low ADU value. Register and composite the white image with the RGB images using luminance-layering color composite techniques. Once processed/composited to satisfaction, save the image as a TIFF.

17. Use general graphics processing software, such as Paint Shop Pro or PhotoShop, to load the TIFF image, enlarge (resample), rotate, crop, adjust gamma, adjust brightness and contrast, and/or apply further functions to produce the desired final product. Save as a least-loss JPEG to retain a high-quality image in a small file size.