How to Make a Composite Star Trail by Josh Campbell

There is a blog post about doing long exposure star trails already on our blog (here).  However, this method advocates using one very long exposure.  There are advantages to using multiple, shorter exposures (several hundred 30 second exposures as opposed to one 8 hours exposure).  For instance, you would be able to use a lower ISO rating or could sequence the photos into a video file in order to show the time lapse.  Here is the tutorial using a photoshop action:

Automated Stacking of Star Trails in PS CS5

Posted on February 24, 2011 by Steven Christenson

NOTE: Our Advanced Stacking Action has been released. It has all the features of the introductory action described below plus much more!

Let’s say you’ve got a bunch of 30 second or 300 second night exposures and now you want to make a star trail out of them.  You already have Photoshop CS5 Standard (or Extended) and you’d rather not monkey around with Image Stacker by Tawbaware or Startrails.exe or StarStax (StarStax runs on Windows, Linux and Macs).

Let’s even assume that you may even already know how to combine those images manually, but are not relishing doing manual steps 20, 50 or 500 times. I’m with you! Chris and Dawn Schur long ago provided an Adobe Action to stack images in Photoshop. As Photoshop has changed, the method for using the Schur action has changed and their action is now obsolete.

Photoshop presents a potentially bewildering array of choices and I found that creating my own action proved more difficult than I thought. So if you don’t want to figure out how to do it we have good news: We have built an up-to-date super spiffy action for you with hopefully copious easy to follow instructions!  And it’s dirt cheap – well actually by the ton, dirt is much more expensive.

In our Star Circle Academy workshops, Harold Davis, Eric Harness and I teach various ways to stack star trails and many other tips and tricks. What I’d like to do for you here, however, is to provide enough detail that you can have  success using our spiffy action to create a stack with Photoshop CS5 Standard Edition – also seems to work with CS3 and CS6.

First you need to download and install the action – which is easy - just order it and you’ll get a nice email with a link. What worked for me was simply to click the link and when (if) the file download dialog comes up, the option to “Open with Adobe Photoshop CS5 (default)” was the first choice:

Open Dialog box for Firefox on Windows 7. Your mileage may vary.

Opening it directly into Photoshop is certainly the easiest if you can convince your browser to let you do that. Internet Explorer also allowed me to open the action with Photoshop – it just took two extra dialogs. Even if you can open the action with your browser you might not see anything happen.

If, however you do not get the option to load into Photoshop directly, don’t fear. You can save the file on disk and then double click it when it finishes downloading.  Google Chrome will download files and save them. The downloaded files will appear at the bottom of your window or in the “Downloads Page” (Ctrl-J).

To verify that the action actually loaded you have to open the Photoshop Actions window. The shortcut to get to open the Actions window is Alt-F9 if you’re using Windows. It might be daisy-leprechaun-fourleafclover on your machine (or perhaps Option-F9). Since you probably haven’t memorized the shortcut try this: Get to the main Photoshop Window. On the title bar you will find File…Edit…Image… and eventually Window Yeah, click on Window.  Actions is near the top of the list of options.

Click Actions and it will launch an ACTIONS window that may look something like this:

If you notice two or more folders named StarCircleAcademy Stack Action it’s because you loaded it more than once on the same machine. One time is all you need, so use the trash can at the lower right of the ACTIONS dialog to delete the older versions. See below for the latest version and a bit about what has changed.

The StarCircleAcademy Stack Action also contains three other actions:

1. DO THIS FIRST! Create Result Frame,
2. Instructions,
3. Load and Stack in LIGHTEN Mode, and
4. Load and Stack in SCREEN mode.

The Instructions action does surprisingly little other than telling you how to find this web page.  Starting with version 4 there is also a “LIGHTEN Droplet” for you to play with when you get really bold. And in version 8 there is a “Save Intermediates” option which is fun to use when creating timelapse animation.

The first thing you should do – especially if you want to make the magic work – is to use the DO THIS FIRST! Create Result Frame.  Once you get the knack of what is going on, you may not need to use that step.

DO THIS FIRST automatically does the following:

• load the first image from the folder containing all the images you will be stacking,
• copy the image to a new document
• close the file it just opened and then
• create a new black image called Results using the file content to determine the proper size and bit depth.

Now let’s go over the whole stacking process from beginning to end, step by step.

1. Close all files you may have open in Photoshop.
2. Use Alt-F9 (Or Window -> Action) to make the ACTIONS window visible.
3. Make sure the ACTIONS window somewhere contains StarCircleAcademy Stack Action v.8 - if not you may not have loaded the action properly.
4. Use File -> Automate -> Batch
5. Change the Set: to StarCircleAcademy Stacker v.8
6. Change the Action to Do this FIRST! (Create Result Frame)
7. Set the source to Folder
8. Use “Choose” to select the folder containing your shots
9. Check the options:
   • Override Action “Open” Commands,
   • Suppress File Open Options Dialogs, and
   • Suppress Color Profile Warnings.
10. Your settings should look like this except your version number may be more recent
11. Press OK.
12. The DO THIS FIRST action will load the first file in the folder and display a message with a button marked “Stop”.
    Press stop.
13. Next a message will show a warning like this…
    Click Stop.  (If you don’t, it will just keep loading images and renaming them to Results and after a while you’ll get bored).
14. Again Click File -> Automate -> Batch
15. Change the Action to Load and Stack in LIGHTEN Mode (Recommended) or if you’re adventurous, try the SCREEN mode.
16. Press OK and watch it run! The action will load each image, add it to the Results, change the blending mode and flatten back to a single image all in front of your very eyes.
17. If you have the ACTIONS window open, it will point to each step as it is doing it.
18. When it’s done, all your images have been stacked in Lighten mode.
19. Save your image where and how you like.

I tried this stacking thing with JPGs and CR2 (raw) images and I was really surprised to see that both worked well.  I suspect you could try it out on your TIFFs and BMPs and whatever else you have.

Enjoy.

If you would like more hands on experience and an opportunity to shoot amazing night skies in amazing locations join us at one of our workshops.

If you’re curious HOW the action is doing its magic, you can poke around in the ACTIONS window. Expanding the “Set current layer” in the “Load and Stack in LIGHTEN” mode you’ll notice the following:

What the Action is doing is Opening an image in your folder, selecting it all, copying the selection, closing the file it just opened and pasting it onto the Results image – which by default creates a new layer. The action then adjusts the blending mode of this new layer from “Normal” to “lighten”. *That* is the magic. The final step is to Flatten the image which eliminates the layers.

Want to go even further? You might be interested in this blog which describes how you can create a “droplet” out of the action.  The droplet is even simpler. You drag files onto the droplet and it automatically stacks them in Photoshop using the StarCircleAcademy Stacking Action. 

http://blog.starcircleacademy.com/2011/02/automated-stacking-of-star-trails-in-ps-cs5/