I've decided to put up a quick tutorial on taking some nice pictures of the night sky in less than perfect light polluted conditions. The results won't be anything like some of those amazing shots obtained from dark sky sites but they will still provide some nice shots. Like this one:
Tools you will need:
- A camera on a sturdy surface (a DSLR on a tripod works best) that can shoot in RAW format (jpegs won't look as nice and are usually to noisy) and shutter speed can be set manually.
- A way to take a sequence of photos in a row (an Intervalometer of some sort)
- Deepskystacker
- Rawtherapee
- Gimp
Steps:
- Locate your target. In this case I aimed my camera at the the Milky Way around the constellation Cygnus.
- Take a couple of test exposures using the rule of 600 and the highest ISO that you can without getting too much noise (a small amount of noise is OK since the stacking will take care of it). Tip: focus on a faraway street lamp with the camera's auto-focus and turn it off, this will get you a focus onto infinity.
- In my case setting the focal length to 27mm and the f-stop to 5.6, ISO 1600 and 10s shutter and daytime white balance, yielded the following result:
Not bad some of brightest stars can be seen and they are in focus! - Set the camera to take a large numbers of exposures in a row (These are your Light Frames). Use an Intervalometer, or in my case I connect the camera via USB to my laptop (using digiCamControl) or my android phone (using qDSLRDashboard). In this case I set the camera for 30x 10sec exposures giving a total exposure of 5 minutes.
- Once the camera is done taking the photos take a few dark frames, by taking 3 shots with the SAME SETTINGS but put the cap back on.
- Finally take a bias shot by keeping the cap on and increasing the shutter speed to the highest your camera is capable of (usually 1/4000 or 1/8000)
- Both the Dark and Bias frames MUST be done at the time your Light Frames are taken
- Now upload the photos to a folder and launch DeepSkyStacker
- Click on Open Picture Files… and load your light frames
- Click on Dark Files… and load the dark frames
- Click on offset/bias files.. and load the bias frame
- Go to RAW/FITS DDP Settings and Check Auto White balance and OK
- Click on Check all
- Click on Register Checked pictures…
- The default setting are OK, you can later play with them or look at some other tutorials on how to tweak them.
- Hit the OK button, sit back and relax. Depending on your number on Pictures and hardware this could take quite a while, my case took around 35-40 minutes on a not to fast laptop. Your mileage will vary!
- When DeepSkyStacker finishes it will create this:
Umm not much to see… - Open the Autosave.tif in Rawtherapee
- Play with the sliders until you get something like this (a future tutorial will deal more with this in detail):
- Hurray, you are almost there. Save it as an 8 bit tiff.
- You probably notice the colour is not quite right and the edges are fuzzy. To fix this develop and save 3 of your best exposures from the set and load them on Gimp.
- Using the G'MIC plugin, blend the 3 photos as layers using the median option to get rid of the stars.
- load the saved 8bit tiff from above as a layer over this one and create a grey scale layer mask. (You may need to do some tweaking to the layer mask's contrast to get better results.
- That's it! You should get something close to this: