Orion 52083 - Manual (Page 19)

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Note: In addition to Average mentioned above, 3 other different combining
methods can be chosen: Sum, Median, and Sigma-Clip. To learn more about
these combine methods, see “Image Processing – Combine Tips”.
10. Now, find a well-shaped (circular) star in the first image displayed. Use the
mouse to center the crosshairs on the selected star and left-click.
11. The next image will now be displayed; center the crosshairs on the same
star in this new image, and left-click again. Repeat this for all the open
images; a chime will sound when you have gone through all the open
images. (If you use the Manual 2 stars align mode, then select another
alignment star in the first image displayed after you hear the chime.)
12. If you find an image that looks poor, you can reject it by clicking the Reject
Image button. Use the Next Image (and/or Previous Image) button to con-
tinue going through the open images after an image is rejected.
Note: At least one image must be used as the reference image for the stacked
images to be overlaid upon. The default uses the first image for the reference
image. If you reject the first image or otherwise want to use another image as
the reference, click the Set As Reference button. If the image currently chosen
as the reference is rejected from the stack, you will not be able to Overlay All
Images.
13. Now, click the Overlay All Images button. All of the selected images will
stack on top of each other to form one resultant image. Click OK.
Adjust the Screen Stretch Window to Medium (or otherwise manually adjust
for best image appearance), and use Save under the File menu to save your
image. You can now perform any wanted imaging processing (see “Image
Processing”). To get the very best images, however, you should subtract “dark
frames” from images prior to stacking with the Combine function.
Dark Frames
To completely eliminate any remaining camera noise, you can take several
“dark frames”, average them, and subtract them from images before stacking.
A dark frame is an image taken with no external light coming into the camera.
What results is an image of the camera’s remaining background noise only.
When a dark frame containing the camera’s noise pattern is subtracted from
images (prior to combining them), the noise is essentially eliminated. The dark
frames can be taken before or after the “light” images are acquired, but if they
are taken beforehand, the dark frame subtraction process can be automated.
Note: To most effectively use dark frames to subtract noise out of resultant
SSDSMI-2 images, it is important to take dark frames close to the actual time
of taking the “light” images. This is because temperature changes will cause
the noise pattern in the SSDSMI-2 to change over time. So, it is best to take
some dark frames immediately before or after the “light” images are taken.