Deep Sky Stacker: calibrate and sum astro pictures

Deep Sky Stacker: calibrate and sum astro pictures

Deep Sky Stacker (DSS – https://deepskystacker.free.fr/english/index.html) is a free software that allows you to calibrate and sum the astrophotos recorded by CCD or DSLR cameras. Calibration is a process that dramatically reduces the defects of pictures such as electronic noise caused by long exposures required for this application and vignetting (light reduction towards the edges of the field of view).

Performing the calibration and adding more images, you can greatly increase the signal/noise ratio and thus obtain a single image file ready for processing. In this article we will make an introduction to the use of Deep Sky Stacker adding some pictures of the Veil Nebula (NGC6960) recorded with a astronomy modified DSLR (“EOS 700Da Cooled” camera) and with a compact 65mm apochromatic diameter telescope and recording also the dark frames. Images were saved by the camera in FIT format. Deep Sky Stacker is a software for Windows and it’s rich of features so, besides this article, we invite you to read the manual in order to explore more its use.

1) Start DSS, a window will open as shown in the image below.

 

Deep Sky Stacker: step 1
Deep Sky Stacker: step 1

 

2) Click on “Open images” and select the images you recorded. Then click “Open”.

 

Deep Sky Stacker: step 2
Deep Sky Stacker: step 2

 

3) Now select “dark files” and select the dark files you registered. Recall that the dark file must be registered with the sensor at the same temperature and they must have the same duration of the light pictures (for this reason it is critical to have, as in the case of “700Da Cooled”, an active control of the temperature). Select “Open”.

 

Deep Sky Stacker: step 3
Deep Sky Stacker: step 3

 

4) Then select “Mark all” to set DSS to use all these images.

 

Deep Sky Stacker: step 4
Deep Sky Stacker: step 4

 

5) Click “RAW / FITS DDP settings” and open the “Settings of the Digital Development Process RAW / FITS”. Using a color camera that recorded images inFIT format not debayered, we must set DSS how to rebuild the color image. If you saved your pictures in FIT format, select the tab “FITS files” and, as camera, set Canon EOS 400D (no need to select the perfect camera model, just a Canon EOS). Then enter 1.5 in the Red and Blue (these parameters are recommended for reflex filter modified for astronomy, if you use an unmodified DSLR set 1 for both), and then select “Adaptive homogeneity direct interpolation (AHD)”. Then press OK.

 

Deep Sky Stacker: step 5
Deep Sky Stacker: step 5

 

6) Then select “Align selected images”, the window “Alignment settings” will open. Check that the setting “Combine after alignment” is active and write 100 in the “Select the __% of the best images and combine them” (if you want to add all the images you’ve recorded).

 

Deep Sky Stacker: step 6
Deep Sky Stacker: step 6

 

7) Click “Combination parameters”, a window will open. Here you can select the mode used to combina images (in the tab “Images” and “Dark”). There are many algorithms available but we suggest the use of “Kappa Sigma cut” leaving unchanged the parameters located to the right. Select “Kappa-Sigma cut” in the tab “Images” and “Dark” and press the OK button to close the window.

 

Deep Sky Stacker: step 7
Deep Sky Stacker: step 7

 

8) Press OK again in the “Alignment settings”,  the window “Combination procedure”, that summarizes all the parameters chosen, will open. Press OK to start the calibration procedure.

 

Deep Sky Stacker: step 8
Deep Sky Stacker: step 8

 

9) Now wait for the end of the procedure. Deep Sky Stacker will subtract darks from the images and align the images calibrated analyzing the stars position. Then it process a sum to create a single image that will be displayed on the screen.

 

Deep Sky Stacker: step 9
Deep Sky Stacker: step 9

 

10) Finally, select “Save picture” and in the window that opens, enter the name of the file to be saved. In the format field, you can leave the parameter “FITS image (32 bit/can – rational). Click “Save” to save the file. You finished the calibration procedure, and you created a single image from your set of pictures.

 

Deep Sky Stacker: step 10
Deep Sky Stacker: step 10