K3's Astronomy - Deep Sky
"When I consider your heavens, the work of your fingers, the moon and the stars which You have set in place, what is Man that You are mindful of him?" -- Psalm 8:3,4

M57 - The Ring nebula - How to get a photograph
Yes, I know, that the result image is not very nice (conditions were very poor), but I think it can be instructive to know how to get the picture. The main failure of this example is small amount of frames. But it was only the first ligth of camera for testing purposes. All processing was done by means of K3CCDTools software, postprocessing was done in Corel PhotoPaint.

1, Taking frames.
At first I took 9 frames exposured 5s with gain 75%. These frames are called raw frames. Here is the best one of them.
As you can see, it is very hards to recognize the stars from hot pixels. That's why the finding the deep sky object is very difficult.
2. Dark frames.
Then I captured 4 dark frames (taken with the same settings as images above, but with shrouded camera). Then I stacked dark frames and created averaged dark frame (DF). The stacking is used to eliminate camera noise (but for real use it better to use much more frames than 4). Here there is the result dark frame:
3. One turning to telescope mount accuracy.
As my telescope mount is only entry level of mounts, it is impossible to do longer exposures without tracking. Because I have no solution for tracking now, I decided to do short 5s exposures of M57.
The effect of tracking inaccuracy is is visible, when we simply stack the frames (DF was applied):

Applying dark frames reduced hot pixels. But inaccuracy of telescope mount caused, that the stars are blurred and darker. The effect of inaccuracy of mount is better visible after applying histogram function:

Now the picture is more clear. You can see the residues of hot pixels. It is caused by small number of used frames for stacking and for calculating average dark frame. The arc shape of stars is now apparently visible. The shape of arc shows, that the tracking error is not caused only by bad polar alignment, but also by slackness of mount (bearings, axles...). The faint fuzzy in the bottom left corner suggest the Ring nebula.

4. Now there is a time for processing.
At first we must exclude the bad frames (blurry stars, etc.) The tracking error can be eliminated by aligning individual frames according to stars. Because of presence of hot pixels the whole job must be done manually in K3CCDTools. Here is the result of stacking aligned frames with applying DF and histogram function:
The hot pixels are darker now. It is caused by aligning (at least one advantage of bad tracking :-)). Stars are now better visible and the Ring nebula is now more apparent.

5. The post processing.
The final image must be processed by specialized graphics software (MaximDL, Corel PhotoPaint, Adobe PhotoShop, PaintShop Pro, ...). They have a lot of useful filters for post processing. Usually I use Corel PhotoPaint. The residues of hot pixels I reduced by applying filter for removing dust and scratches from scanned images. After that I resized the image to 50% reduce noise and applied some level equalization functions. The amount of various functions and their settings is practically unlimited, so there a lot of space for playing with picture. Here are two of my various results:

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Last Update: 8.10.2001