What is DeepSkyStacker?
DeepSkyStacker is a freeware for astrophotographers that simplifies all the pre-processing steps of deep sky pictures.
- Registering
- Stacking
- Simple post-stacking processes to quickly view the final result.
- Saving the resulting image to a TIFF or FITS file (16 or 32 bit)
After a shooting night you give all your pictures (light frames, darks frames, offset/bias frames, flat frames) to DeepSkyStacker and you go to bed. The next morning (or is it afternoon?) you can see the result and start post-processing.
Light, Dark, Flat, Bias... What are they and how to create them?
(if you are wondering how all the files are used during the calibration process you can have a look here)
Light Frames
The Light Frames are the images that contains the real information: images of galaxies, nebula...
This is what you want to stack.
Dark Frames and Dark Flat Frames
The Dark Frames are used to remove the dark signal from the light frames (or the flat frames for the Dark Flat frames).
With DSLRs and CCD Camera, the CMOS or CCD is generating a dark signal depending of the exposure time, temperature and ISO speed (DSLR only).
To remove the dark signal from the light frames you use a dark frame that contains only the dark signal.
The best way to create the dark frames is to shoot pictures in the dark (hence the name) by covering the lens.
The dark frames must be created with the exposure time, temperature and ISO speed of the light frames (resp. flat frames).
Since the temperature is important try to shoot dark frames at the end or during your imaging session.
Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master dark or master dark flat.
Bias Frames (aka Offset Frames)
The Bias/Offset Frames are used to remove the CCD or CMOS chip readout signal from the light frames.
Each CCD or CMOS chip is generating a readout signal which is a signal created by the electronic just by reading the content of the chip.
It's very easy to create bias/offset frames: just take the shortest possible exposure (it may be 1/4000s or 1/8000s depending on your camera) in the dark by covering the lens.
The bias frames must be create with the ISO speed of the light frames. The temperature is not important.
Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master bias/offset frame
Flat Frames
The Flat Frames are used to correct the vignetting and uneven field illumination created by dust or smudges in your optical train.
To create good flat frames it is very important to not remove your camera from your telescope before taking them (including not changing the focus).
You can use a lot of different methods (including using a flatbox) but I found that the simplest way is to put a white T shirt in front of your telescope and smooth out the folds. Then shoot something luminous (a flash, a bright white light, the sky at dawn...) and let the camera decide of the exposure time (Av mode),
The flat frames should be created with the ISO speed of the light frames. The temperature is not important.
Take a few of them (between 10 and 20 is usually enough). DeepSkyStacker will combine them automatically to create and use a clean master flat frame.
by Ryan Leemhuis Photography
