Star Trail Stacking
Part I of the May Photoshop challenge
Blending multiple exposures into a star trail photo, or star trail stacking, turned out to be much easier than I expected. Simply import and process. The computer does all the job but it does indeed require a lot of processing power and RAM. The reason for stacking rather than doing one long exposure is be able to control the exposure. If you do a single long exposure the sky usually becomes too bright.
Now I’m facing a different problem though, namely the gaps between the stars! This is a, maybe even expected, side effect of using this method for star trails. The reason for this is not only the pause between the exposures but also the in camera processing, which rounds edges. There are a few ways to solve this problem, which will be my next thing to look into.
The most difficult part of making star trail photos is to wait for the exposure to finish. One way is to have two cameras, set one up with the intervalometer and photograph something else with the other camera meanwhile. But since I plan to do my next star trail photos in the city, leaving a camera by itself is not an option. I just have to be patient or use a longer lens.
I noticed during this attempt that a completely clear sky is preferable. Towards the end of my shooting some clouds sailed in and obscured the sky and caused some weird color effects and more gaps. Because of this I couldn't use all of my exposures. If I’m lucky with the weather I might get at least one clear sky before the stars disappear into the summer night. Otherwise I will just have to wait until August.
There are (at least) two ways of blending the stars in Photoshop. Below are some quick notes how to do it:
1. -file → script → load into stack | select files → ok | select all layers → select blend mode: “lighten”
2. -file → script → load into stack | select files → check the box: “create smart object after loading” → ok | layers → smart objects → stack mode → maximum