Note: This entry was authored by Kip Pauls over on the Yahoo Group with the help of Bill Logan and Patrick W. I’ve just entered it here to make it more widely available. Kip Updated this on 05.02.07

This manual is a simplified version of the Nebulosity manual. It’s to help those that are NEW USERS to get up and running a fast as possible. I don’t go into detail (unless it is requested) of why the process is done the way it’s done. The manual that I have made is by no means the law of processing using Neb. I encourage input from others when using this manual. Remember, the goal of this manual is to keep it simple for the NEW user. I’m sure that this manual will be updated over time. If there is something that isn’t clear.... check the Stark-labs yahoo group. Enjoy!! Kip Pauls

Status Bar: At the bottom of the window is the status bar. The status bar gives you information about what Neb is doing and data about the image. The Status Bar is divided into 4 panels.

1. The right-most panel always tells you what Nebulosity is doing. It may read “Idle” (it’s not doing anything), “Capturing”, “Processing”, etc.

2. Next to that, (to the left) is a panel that shows you the X and Y coordinates of your cursor position and the intensity of the signal at that position. It will look something like this, 372,231 = 5437. Generally the “signal” is referred to as the ADU. In the example that I have given here the X coordinate is 372 and the Y coordinate is 231 and the ADU is 5437. You may hear people talk about not exceeding Max Pixel or ADU. Max ADU is 65535. Another term they use is ‘hitting the ceiling’.

How to read the Histogram: Knowing how to read the histogram is important in getting good images. You can use it to analyze during capture and processing.

Here are some examples of reasonable histograms for single images - things you might see when you’re capturing images:

Here are some examples of poor histograms from single frames - things you should avoid when capturing images:

What makes these good or bad? Look at them and ask the following:

1. Is all of the data to the far left? If so, your entire image is faint and you should increase your exposure or gain if possible. Generally when you are capturing, this will be the case. What you will need to do is move the cursor over the image and see what the ADU says. I like to have the brightest star around 45,000 ADU when capturing. However, if I am capturing a dim object like a galaxy, I will ignore this rule and take a long exposure of 5 minutes or so in order to pick up the detail in the galaxy. Nebulae, like M57 can usually be captured in a 30 second exposure just to give you an idea.

2. Do you see a nice curve that trials off to the right just before you get to the edge of the Histogram? If so, you’ve got a nice exposure and are making the most of your data. TO HELP AVOID CONFUSTION I NEED TO LET YOU KNOW THAT WHEN YOU CAPTURE ONE IMAGE AND LOOK AT IT, IT MAY BE TO THE LEFT AND NOT REALLY TRAIL OFF FAR TO THE RIGHT. WELL, IT WILL DROP OFF TO THE RIGHT RATHER RAPIDLY BECAUSE IT IS ONLY ONE EXPOSURE. WHEN YOU STACK ALL OF YOUR IMAGES, THEN, AND ONLY THEN WILL YOU SEE A NICE CURVE THAT TRAILS OFF TO THE RIGHT!!

3. Do you see that instead of trailing off smoothly near the right edge, the curve ends abruptly at the right edge? That is, it bangs into the right edge? If so, you’re saturating a lot of the pixels in your image and should likely use a shorter exposure or less gain.

4. Are you cutting off hard on the left edge? If so, use more gain, more offset, or greater exposure duration. Remember, the more gain you add, the more noise you will have in the image. I generally run with the gain number set to 25 but this will vary from camera to camera.

5. If you stack a series of your images and the data is cut off on the left and right sides of the histogram, you need to boost your exposure.

(Craig) In all of this what you’re trying to do is to get the most information from the image as possible. If your sky goes to zero (banged into the left side of the histogram) you have lost information. Subtle details in a galaxy or nebula are all at zero and no amount of stretching will bring that out. The information is lost. Likewise, on the right of the histogram, if you bang into there, differences in intensity in, say the core of a galaxy are lost as they all have the same value (65535). No amount of stretching will pull them apart as they have the same exact intensity. In my opinion, 0 is more evil than 65535. Galaxy arms and nebulae become zero and those we really want. Bright cores of stars become 65535 first and variable shades of (bright) gray there mean less to me than variable shades of (dim) gray in a galaxy arm.

Now, when processing and stretching the image, your goal is to stretch that histogram out. During the final stages of processing, you’ll likely clip the histogram there at the top (right) and bottom (left), letting some things go all-white and some things go all-black. That’s fine, but do this as late in processing as you can. Once you hit zero or 65535, you’ll never come back to pull out detail there. Here are some samples of processed histograms:

How to use the Focus feature in Neb.

1. Chose a star that is around 5th or 6th mag.

2. Set duration for 1 second and click ‘Frame and Focus’. Once the frame has cycled for 1 second then click ‘Abort’

3. Now click ‘Fine Focus’ then click on a star in the image. Several things happen. A graph, star and numbers will appear. The frame will cycle every second and you will see the graph change along with the numbers. As you focus, the graph will tell you how the focus process is doing. You want the graph and the numbers to be high as possible. As your focus becomes sharper the graph will rise and the numbers will rise too. If the graph and numbers start to drop, you have gone to far and you need to turn the focuser the other way. Take your time during this process and let the vibration settle down before making additional adjustments. What do the numbers mean? M- is the measurement of the brightest pixel, m- is the average of the 3 brightest pixels, and s- is the sharpness.

Image Capture

1. Select your camera.

2. First set the duration to the desired duration that you wish and the number of exposures.

3. Click on ‘directory’ and select where you want the files to be saved at.

4. Click ‘capture series’ and the process is started. Program will chime when exposure is complete. You can select the program to chime after every frame or when the series is done. You can use ‘Preview’ to see how the shot will look before you capture the series.

How to process your images with Nebulosity.

(It is recommended to capture all of your shots in the RAW format and convert to color during processing).

1. First combine all your Dark frames together. You will use this process for your Bias and Flats too, However to keep it simple we will just do Dark frames. To do this, go to the menu and select the PROCESSING menu then go down to where is says “Align and Combine Images”. The latest version of Nebulosity 1.4.8, has changed a little. Now you will select “Align and Combine Images” from the Processing menu. A window will come up and you have a choice of different alignment options. When stacking Dark, Bias or Flat frames you will click “None (fixed)” from the alignment window. You also need to uncheck ‘Adaptive Scale Stack to 16 Bits” You only uncheck this when stacking Dark, Bias or Flats. When you have done that click OK and a window will come up and you will select The Dark frames. Label it “DARKMASTER” or whatever you want.

2. Now you’re going to apply the “DARKMASTER” to the light frames. Go to “Processing” menu and select Pre-process B&W/RAW. Don’t worry about the BIAS, FLAT OR AUTOSCALE DARK were just going to do the Dark frame. Click DARK and select your “DARKMASTER” that you made in step 1, then click DONE. Another window will come up and ask you to select your ‘LIGHT FRAMES’ Click on the first light frame then hold down the shift key and select the last light frame then hit open. It will now process the frames and label them as “PPROC” The dark frame has now been applied to each image and labeled PPROC.

3. Now, that the light frames have been applied, the next step is to convert them to color and square the pixels (It is recommended to capture all of your shots in the RAW format and convert to color during processing) . Go to the “PROCESSING” menu and select ‘Batch Demosaic + square’. Now select all of the PPROC frames then click open. Each image has been squared and color converted and is now labeled ‘RECON’

4. Now it’s time to Stack. This is the best part and makes it so easy for you. Select ‘ALIGN AND COMBINE IMAGES from the Processing menu. The alignment window will pop up. Click “Save Stack” for the Output Mode and click “Translation” from the Alignment Window. Make sure ‘Adaptive Scale Stack to 16 Bits” is checked. Click OK and a window will pop up, now select the ‘RECON’ frames then click open. At this point, you’ll notice the cursor has changed to a cross-hair. Your goal now is to identify the same star in each image. Pick a star that is fairly isolated and that is not saturated. If you have been using a tracking program and there isn’t much drift you can just press Ctrl-Click to keep the guess through all the images. You can look down at the lower left of the processing screen and see the instructions on what to do. Once it’s done the final image will appear. Refer to the original manual for other alignment options and how they work. 5. Save

6. Now you need remove the skyglow and bring out the detail. First, Go to Image menu select Adjust Color Background (offset). Don’t mess with the sliders just click DONE.

7. Now go into the Image menu and select Levels / Power Stretch this is where you will bring out the detail. Look at the histogram. What you want to do is have the histogram to have a nice curve that trials off to the right just before you get to the edge of the Histogram (refer to the How to Read the Histogram.) Use the sliders to do this. That’s it. For more advanced processing techniques, take a look at the advanced users guide.