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Aligning and stacking with Nebulosity

PostPosted: Mon Oct 24, 2011 11:04 am
by smerral
This is just a quick outline of how I stack images in Nebulosity. There is a lot more to this program and features which I haven't used. If you are a more experienced user feel free to add/modify these instructions.

OK, if you are using a one shot colour camera and you have saved your captures in RAW format you will need to debayer/demosaic the images. The same applies to darks and flats. If you have saved in RGB colour then you can ignore this step.

1 - Open Nebulosity and go to the Batch menu:

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Select your images and Nebulosity will debayer and save each capture with a prefix.

2 - Create a master dark and flat.

First you need to make a master dark/flat. This is done by simply stacking the individual dark frames:

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Click on this and select "none" for align:

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Click OK and Nebulosity will stack. Call it master-dark and save. Repeat for flats.

3 - Apply darks and flats. Go to Batch again and pre-process colour images:

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Then you get this:

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Click Dark, OK and select your master-dark:

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Click OK again and select your lights. Nebulosity applies the darks and again adds a prefix to each capture. If you have a master-flat then you simply repeat the process using the images which have had the darks applied.

4 - Align and Stack.

Go to batch again, align and stack. This time we need to choose between Translation, if you have a EQ mount, or Translation + Rotation if you have a Alt-Az mount:

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Hit OK and select your pre-processed images.

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Now click on a star on the left or right-hand side of the image; automatically Nebulosity loads the next frame. Keep clicking on the same star till you've gone through all the frames. If you need to skip a frame due to star trailing etc. hold down the shift key while clicking and that frame will be skipped. If you're using Translation only, then at the end of the run Nebulosity will automatically stack the images. If you selected Translation + Rotation then a cross will appear in the circle over the selected star. You then need to choose ANOTHER star at the other side of the image and repeat the process. This time the skipped frames have already been dropped, so it is just a matter of repeatedly clicking on the star. Once again Nebulosity will automatically stack.

5 - Saving and post-processing.

You need to save as a fits file initially, but once you've done that you can just go to the File menu and save in a variety of formats.
At this stage you can close Nebulosity and just re-open your saved image in your graphics package for further processing. However, I have found the following useful.

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And this one, about a 1/3 of the way on the slider:

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Well that's it! Believe me, it really sounds more complicated than it actually is!
I hope this helps! :)