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Canon-Nebulosity Tutorial for Beginners - page 7 / 9





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“Done.” A new window will appear and ask you to select your light frames. As before, click the first light frame “TrifidRaw_001.fits” and at the last frame, press “Shift + left click” and all the light frames will be highlighted. Click “OPEN.” It will now dark- subtract all the frames and label them as “PPROC.” This may take a couple of minutes so it may be time to grab a cup of coffee or use the restroom.

Color Conversion and Squaring. A message will appear at the bottom notifying you that the images have been processed. The next step is to convert them to color and square the pixels. Under the “Processing” menu, select “Batch Demosaic + Square”. Now select all of the “PPROC” frames then click “OPEN.” As each image is being processed, Nebulosity will label them as “RECON.” Again, this will take some time so relax or find something else to do. Sometimes watching the process is about as exciting as watching paint dry or an apple turn brown. At about at this time, you probably wished that you had 2 GB of RAM!!

Now it’s going to get exciting. It’s time to stack! This is the best part and Nebulosity makes it so easy. From the “Processing” menu, select “Align and Combine Images.” The “Alignment/Stacking” window will pop up, but this time click “Save Stack” for the Alignment Method, select the “Translation” button. Time to pause here to explain the choice of options.

Translation” means shifting (up, down, left, and right) only. This is appropriate if all your images were taken, one right after another, through, on piggybacked on, an equatorially mounted telescope.

Translation + Rotation” means shifting and rotating. This is appropriate if your telescope was tracking in alt-azimuth mode or if you think the camera or lens may have twisted slightly between exposures.

Translation + Rotation + Scaling” means all of that, plus stretching (changing size). This is rarely needed, but it might be appropriate if the image size of your telescope changes when you touch up the focus.

Make sure “Adaptive Scale Stack to 16 Bits” is checked. Click OK and a window will pop up. Select all of the “RECON” frames and then click “OPEN.” After the computer has retrieved all of the “RECON” images, the cursor will change to a crosshair. Use the zoom-in button so that you can see a close-up of the stars in the center of the frame. Your goal is to identify the same star on each good frame and delete bad frames from star movement especially if you have manually guided. If you have zoomed in enough, you can actually see the pixels of a dim star. Move the cursor over that star and click it. An hour-glass will appear indication that the image is being processed. When finished, you should see red circle around the same star making it easy to identify (if you selected Translation + Rotation, you will select the first star and when finished with all frames, will ask you to pick the second star located well away from the first star. When the second star is selected, there will be a red circle with an “X” on the first star. The second star will have a green circle). If you have good tracking, you can press Ctrl-Click to keep

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