AIP4WIN: Beginner

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Submitted by bkloppenborg on 04 February 2010

This tutorial provides a step-by-step procedure for processing digital images obtained in “Raw” format to yield insturmental magnitudes. The instrumental magnitudes will be used in the “Finishing Analysis” portion of our tutorial. You will need AIP4Win 2.4.0. If you don’t have this version, a free update is available from Willmann-Bell at: http://www.willbell.com/aip4win/AIP.htm. The tutorial assumes that, in addition to a series of sequential star field images, you also have dark frames, flat frames and flat-dark frames. If your camera has automatic noise reduction, you can use this feature when taking your star and flat images and eliminate the need for darks and flat-darks. Before you begin the tutorial the images from your camera (or tutorial data files) should be copied to a directory on your computer. This will simplify and speed up processing.

 

Using AIP4Win, we will:

1. Convert images in “Raw” format to green-channel grayscale “FITS” images.

2. Setup Calibration

3. Calibrate and stack the images

4. Obtain “instrumental magnitudes” for the variable and comparison stars.

After completing these steps, the instrumental magnitudes are entered into a spreadsheet to yield calibrated magnitudes suitable for submission to AAVSO.

This tutorial was written by Tom Pearson with editing changes by Paul Lloyd, GMara and bkloppenborg.

 

AIP4Win Processing

 

Step 1. Convert images in “Raw” format to green-channel grayscale “FITS” images.

 

1. After opening AIP4Win, go to the menu across the top of the screen and click “Preferences/ DSLR Conversion Settings”.

 

 

2. A dialog box will open. Click the button: “BILIN” for the De-Bayerization Algorithm. Click the button: “DeBayer, Convert Color to Grayscale.” Set the red and blue parameters to zero and the green parameter to 1.0. Click on “Save” and “Done” at the bottom of the window.

 

 

Now that AIP4WIN is setup to open the green pixel data in grayscale, we need to open and save all images as FITS files.

 

3. Click “File/ Open Image…” at the top of the screen. A dialog box will open. At the bottom of the box, choose “Digital Camera Files” as the file type. At the top of the box find the folder containing your star images. From the list of images select your first star image to open.

4. Back at the top of the screen, click on “File/Save as FITS…”. Save the image as a “*.fts” file, e.g., “gray3024.fts”. When asked, save the image with the 32-bit floating point option (the default).

5. Close the image window.

6. Repeat this process for each of your star images, darks, flats and flat-darks.

 

Note: I have tried stacking the images first and then doing a single conversion but this method does not work for some reason. So, I go through the drudgery of opening each of my 40 images (10-star, 10-dark, 10-flat, 10-flat-dark) and converting each to gray scale individually.


Note: If you are taking images using your camera’s automatic noise reduction feature, you only need to use flat frames processed in this step. There is a glitch in the program, however, that requires you to process at least one dark frame. Here's the work around:

1. In the "Setup Calibration" window, load and process one dark frame

2. Uncheck the box at the bottom that says "Subtract Dark Frame".

 

 

Step 2. Setup Calibration.

 

We will use the "Standard Calibration" method in AIP4WIN.

 

1. At the top of the screen click on “Calibrate/Setup”. A dialog box will open.

 

 

2. At the top of the box, select the “Standard” calibration protocol.

3. On the dark tab, click on, “Select dark frame(s)”. A dialog box will open to select your dark frames. The button will turn green when your frames are selected.

4. Click on “Process dark frame(s)”. The button will turn green when processing is complete.

 

 

5. Click on the “Flat” tab and select your flat frames as above.

 

 

6. Check the box “Subtract flat-darks”

7. Select your flat-darks and click on “Process flat frame(s)”.

8. When processing is complete, all buttons should be green. The “Subtract Dark Frames” and “Apply Flat Field Correction” boxes should be checked. Also, look at the buttons across the top of the screen. The “Calibrate Image” button (red circle around letters CAL) should be illuminated.

9. Close the dialog box.

 

Note: If you are taking images using your camera’s automatic noise reduction feature, you only need to use flat frames processed in this step. There is a glitch in the program, however, that requires you to process at least one dark frame. Here's the work around:

1. In the "Setup Calibration" window, load and process one dark frame

2. Uncheck the box at the bottom that says "Subtract Dark Frame".

 

Step 3. Calibrate and stack the images.

 

1. At the top of the screen click on "Multi-Image/Auto-Process/Deep-Sky". The AutoProcess Multiple Images dialog box will open.

 

 

2. At the top of the box, click on “Select Files”.

3. Open the FITS image files to be stacked.

 

Note: For the images to appear in numerical order, you must select the last image in your sequence first, then hold down the shift key and highlight the first image. Otherwise, the last image in the sequence will be at the top of the “Select Master Frame” list in #5 below. We want the list to be in numerical order to avoid tracking errors while stacking the images.

 

4. On the “Pre-Process” tab, check the “Calibrate images” box.

 

 

5. On the “Alignment” tab, click on the “Select Master Frame” window and choose the image at the top of the list.

 

 

6. When the image opens, check the “Two Star” alignment box.

7. Increase the track radius to 10 (or higher if tracking problems are observed in your stacked image).

8. On the “Image Display Control” dialog box zoom out to about 33%.

9. On the “master” image, click on the first alignment star. Then click on the “Star1” button on the “Alignment Tab”. A yellow number 1 should appear next to your star. Repeat the steps for Star 2. For best results the two stars should be on opposite sides of the image.

10. Back on the “AutoProcess Multiple Image” box, click “OK” to start image calibration and stacking.

11. If no tracking problems are observed (i.e., all stars are points and not streaks), save the stacked image by clicking “File/ Save as FITS…”. Otherwise go back to #7 and increase the radius until a satisfactory stacked image results.

12. Close the “AutoProcess Multiple Image” dialog box.

 

Note: If you have been working with the three images from the sample data file, your stacked image should look something like the example here. Don’t be alarmed by the bright area in the lower right. There was a full moon near Auriga when the images were taken.

 

 

Step 4. Obtain “instrumental magnitudes” for the variable and comparison stars.

 

1. Locate your variable star and comparison stars (three or more) on the stacked image.

 

Note: I use the free star atlas Cartes du Ciel to help find the stars. This program allows you to create a red frame overlay the size of your stacked image. You can also rotate both the frame and the star chart to match the orientation of your image. Clicking on any star in the atlas produces a box containing the star name and particulars. Other planetarium programs could do much the same, but this is a readily available free one.

 

 

2. At the top of the screen select “Measure/Single Image Photometry Tool (SIPT)”. This will open the Single Image Photometry dialog box.

 

 

3. At the bottom of the Image Display Control dialog box, zoom in on your variable star.

 

 

4. Back on the Single Image Photometry dialog box, click the “Settings” tab and adjust the “radii” so that the aperture (inner circle) is sized approximately as indicated on the image above (See the AIP4WIN Handbook section 10.1.2 for an explanation).

5. Adjust the annulus (outer circles) as appropriate for the aperture. One thing to avoid is getting other stars inside either the aperture or annulus. To show any change you make to the setting(s), click on the variable star – this deselects it – then click on it again; the changes you have made will now be displayed.

 

Note: Steps 1 through 5 are performed only once for a particular imaging series. These settings can remain unchanged as long as the same stars are being imaged using the same exposure settings, i.e., time, F#, ISO and lens focal length. For a different star field or different camera settings, choose the brightest star (largest diameter) in the set of variable and comparison stars to set your aperture and annulus size.

 

6. Leave the remaining items on the “settings tab” at their default values for now. Later, you can adjust the “zero point” to make your instrument magnitudes approximate the calibrated magnitudes.

7. Click the “save” button on the “Settings” tab.

8. Now, click on the “Results” tab.

9. On the “Image Display Control” dialog box, zoom back out to about 30%.

10. Shifting to your star image, click on your variable. Record the Raw Instrumental Magnitude that appears at the bottom of the “Result” tab on the “Single Image Photometry” dialog box. Also, check the value of “PV max.” This number should remain well below the saturation level for your camera (4096 on my Canon 20D).

11. Repeat step 10 for each of your comparison stars.

 

 

This last figure shows the stacked image with stars used in “Finishing Analysis” labeled.

They are: V-eps Aur, C1- lam Aur, C2 – rho Aur, C3 – mu Aur, C4 – ome Aur, C5 – sig Aur, C6 – 58 Per.

 

Note: You can also generate a report containing the instrumental magnitudes by using the following steps:

a. On the Single Image Photometry Tool, click “Get Magnitude” at the bottom of the box.

b, Open the AIP DataLog from the menu at the bottom of the screen. Save the data log. The file contains imaging data that includes star labels (V, C1, C2, etc.) and Instrumental magnitudes that will be needed in finishing analysis.

 

You're done!

Now that you have obtained insturmental magnitudes, you are ready to compute calibrated magnitudes. The DSLR Documentation and Reduction team has created spreadsheets to help you finish your analysis.

 

 

 

 

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