To start:
1. Acquire the deep sky object into the field of view of your eyepiece, and
center it in the eyepiece’s field of view. Focus the eyepiece with the tele-
scope’s focuser. Make sure your equatorial mount is well polar aligned, and
the R.A. motor drive is on and engaged.
2. Remove the eyepiece and replace it with the SSDSI-II.
3. Precisely focus the camera by using the telescope’s focus knob and the
Focus setting in the Camera Control Window. Set the Mode to Light Color
1x1, and try an exposure time of a few seconds to start. Use the Medium
setting in the Screen Stretch Window. The focus point for the SSDSI-II will
be approximately 15mm inwards from the eyepiece’s focus point. If you are
having trouble determining best focus, try focusing on a bright star near
the deep sky object. If there are no suitably bright stars in the camera’s
field of view, you may need to slew the telescope away from the deep sky
object to a bright star, focus on the bright star, and then re-center the deep
sky object in the camera. When you have a good focus, press the Stop
button in the Camera Control Window
4. Now, in the box under the Mode box in the Camera Control Window,
select AutoSave. Set the number of images you would like the camera
to take under Autosave (start with 5 or so), select the file folder in which
you would like to save the images with Folder, and enter in a Base file-
name for the captured images. Typically the name of the object being
imaged, such as “OrionNebula1”, will be entered here. If “OrionNebula1”
is the Base filename, and you choose to Autosave five images, then the
images will appear in the selected file folder as “OrionNebula1_0001.fit”,
“OrionNebula1_0002.fit”, “OrionNebula1_0003.fit”, “OrionNebula1_0004.
fit”, and “OrionNebula1_0005.fit”. Try exposures of 30 Seconds to start.
5. Click Expose, and the camera will commence taking the images.
Note: When the camera is taking long exposure images, it is critically important
not to touch, shake, or otherwise disturb the telescope, or a blurred image will
result. Also, make sure no surrounding light shines into the telescope during
the exposure.
Now that you have multiple images of the deep sky object, we will combine the
images to form one high-quality resultant image. To do this:
6. Select Open from the File menu. Find the folder you indicated with Folder,
open it, and select all images for stacking using the mouse left-click and
the Shift key. All of the individual images selected will open in Maxim DL
Essentials.
Note: In order to combine images, the images must first be opened in Maxim
DL Essentials
7. From the Process menu, select Combine.
8. In the Select Images window, click Add All. Then click OK.
9. The Combine Images window will appear. For Align Mode, choose Manual
1 star – shift only. (If you have field rotation due to a poor polar alignment,
then you can use the Manual 2 stars align mode.) In the Output box, select
Average. Make sure the Use Centroid and Auto Next boxes are checked.
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
SSDSI-II 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 SSDSI-II to change over time. So, it is best to take some
dark frames immediately before or after the “light” images are taken.
