Method 3: Using Advanced Stacker Plus
Another way to stack star trails with some options not natively available in Photoshop is to use the Advanced Stacker Plus Photoshop plug-in, available for about $30 as a download from the Star Circle Academy. (In the interests of full disclosure, I need to point out that I'm a friend of Steven Christensen, the author of Advanced Stacker Plus. As colleagues, Steven and I occasionally co-teach night photography workshops.)
In addition to enabling a Photoshop layer stack using the Lighten blending mode, Advanced Stacker Plus saves incremental partial stacks as it operates, meaning that you can easily use it to create time-lapse sequences, and it may consume less system resources than the Statistics script. Advanced Stacker Plus also provides a number of special effects (see Figure 11), such as the ability to add the look of a "comet head" to the front of a star trail.
Figure 11 Some of the Advanced Stacker Plus special effects, shown in the Photoshop Actions pane.
To get started, make the Background layer black in the image window. Load Advanced Stacker Plus using the File > Automate > Batch command. Use the Choose button in the Source area (see Figure 12) to tell Advanced Stacker Plus where the folder of star trails exposures is located on your computer. Next, in the Destination area, use the Choose button to indicate where you want to output the results. With the basic settings in place, the layers are combined using the Lighten blending mode.
Figure 12 With the Advanced Stacker Plus plug-in loaded in Photoshop, the Automate > Batch command takes you through the steps necessary to create a star trail stack.
Part of the appeal of Advanced Stacker Plus is that, in addition to the Lighten blending mode, it provides some useful utilities (see Figure 13), and it can be used to create a number of interesting—if not entirely authentic—cosmologic effects (see Figure 14).
Figure 13 Special effects and utilities are available in the Advanced Stacker Plus menus.
Figure 14 To create this image extending from sunset to sunrise, I stacked 139 four-minute exposures, shooting each exposure at f/4 and ISO 400.