Tag Archives: StarStax

Advanced Star Trail Tricks

Published: Oct 11, 2012
Last Update: February 14, 2018 (remove Flash)

I have been playing with Star Trail processing for quite a while.  Ever since I wrote the StarCircleAcademy Stacking Action I’ve been tweaking processing to try different things. Sometimes failure is inevitable, sometimes… well, you’ll see.

First, you may want to look back through my earlier columns on shooting and processing star trails because this is not a primer on star trails – it builds on what I’ve previously written and this is not a good place to try to understand what stacking is.

Second, please understand that I use a variety of tools but almost all of my more successful endeavors end up as layers that are combined in Photoshop (CS5 at the moment).  You could combine your layers in GIMP if you don’t have Photoshop, but you’ll be out of luck if you try to use Lightroom.

Here are my star trail effects:

  1. Smoothee – Averaged sky and/or foreground to reduce the grittiness that sometimes results from brighten stacks. I’ve been espousing this for quite a while. See the Simple Astrophotography Processing Technique.
  2. Blobulous – stars at the beginning (or end) of a trail are made to stand out from the rest of the trail.
  3. Comets – star trails appear to grow brighter and the end of the trail looks like the nucleus of a comet.
  4. Streakers – Like comet only the trails are longer
  5. Blackened – A clever trick removes sky glow from light pollution, the moon, or twilight.

And of course you can make “Blobulous Comets” and “Blobulous Streakers” and “Blackened Smoothee Comets” and more.

Building Blocks

To creatively combine exposures, I usually create the following stacked frames.

  • Dark (Darken in Image Stacker/StarStax)
    The darkest elements emerge – especially the hot pixels
  • Brighten (aka lighten) stack
    The Brightest of everything is present, including hot pixel and more noticeable noise
  • Average
    Contrast is reduced, smoothness increased.
  • Additive (called “Stack” in Image Stacker)
    Hot pixels become really bright.
  • Scaled (called Stack/Average in Image Stacker)
    Allows some increase in brightness but more smoothness, too. Experiment with different divisors.

Normally I create all of these combinations using Image Stacker against my JPG files because it is really easy to do.  I end up with a set of frames something like these although I’ve significantly brightened them so that they are easier to see.


In a Nutshell: Combine the Average stack over the Brighten stack using Normal mode at 45% opacity.

I’ll start with the Smoothee technique since it’s probably the easiest to do and perhaps the easiest to understand.  The problem with “Brightness” (or lighten as it’s called in Photoshop) is that it will also pick up all the hot pixels, and the brightest bits of noise.  Averaging on the other hand tends to smooth out everything except for truly hot pixels since most noise is random. By putting an averaged stack as a layer over the brighten stack and then adjusting the blending modes and opacity you get a smoother sky and foreground.  Exactly what settings to use depend on the images, but surprisingly many of the blending modes for the Average layer work here including Darken, Multiply, Overlay, and Normal. The starting place for Opacity is about 45%.

Hint: You can also use an Additive stack instead of the average stack but usually only the Normal blend mode will work.  For even more fun combine the Additive stack and the Average stack.

For additional smoothness you can also subtract the “Darken Stack” while adjusting the opacity to prevent halos and weirdness.


In a Nutshell: Add one of the single frames more than once.

What do “Blobs” look like? Like this…

“Fat Star” processing.

There are two ways to produce “Blobs”. One way is to add “Comets” to a smoothed star trail. The other is to simply pick an image (usually the last one in the set) and add it in using “Add” or “Screen” mode. To make the blob more pronounced duplicate the last frame so it’s added twice. BUT remember when you add in any single image the hot pixels are going to come out… and even more so if you add an image twice.

Comets and Streakers

These two techniques require some fancy stacking techniques. Fortunately I’ve created an action to do all the fancy stuff.  I’ll be rolling out the action and the explanation to my Photo Manipulation Webinar participants first <NOTE: The Advanced Stacker PLUS action has been released and is available for purchase in our store>.

Oh, here is a peak at what the Comet action looks like:

What's The Point?

And here is what an animation of comets might look like:

Star Rise



I know you’re going to ask so let me save you some typing. Except for the “Comet” image above, all images used in these illustrations were taken during the Ancient Bristlecone Pine Workshop in the Patriarch Grove on White Mountain, East of Bishop, California.

The 34 or so images that I’ve combined in the examples above were all taken with the following settings: Canon 50D, ISO 400, f/3.5, 79 seconds, 10-22mm lens at 15mm.

Easy (HDR) Blending with Stacking Software

I’ve been teaching a “Catching the Moon” webinar approximately monthly. The focus of that course is to teach how to properly expose for the moon, how to catch the moon aligned with your favorite landmark, and how to determine the optimum light scenarios.  The webinar is based on my Alignment 1 and Alignment 2 articles with a healthy dose of additional material including some private material for students only.

One of the most difficult aspects of getting a moon alignment is that there is a pretty small optimum time window for getting an exposure.  Shooting earlier or later makes the foreground illumination and the moon illumination all but impossible to get both exposed properly in a single shot.

Here is an example of a single shot where the lighting was pretty close to perfect (though you can see the moon is a bit over exposed).

A Perfect 10 [5_057646]

However later that evening the sunset occurred quite a while before moon rise, so the sky and foreground were much darker.  The photographer faces a conundrum. Expose for the foreground or expose to preserve moon features.

On the left is a 30 second exposure prior to moon rise (though a tiny bit of the moon is in fact visible). On the right a 1/25th of a second exposure. Both taken on a tripod at f/9, ISO 250, 444mm effective focal length.  The problem is that a longer exposure renders the moon as a white featureless blob or streak (see below for an example). However exposing for the moon as on the right renders the foreground all but invisible.

What to Do?

There are a couple of simple alternatives. One is to bring both images into Photoshop. Make both images layers, the moon on top of the background and combine the two images using “Lighten” blending mode.  That will work very well and it’s essentially what happens when using the StarCircleAcademy Stacking Action. But that action, and even Photoshop are overkill for this situation.

Free Solution!

Fortunately Markus Enzweiler offers a free solution called StarStax that runs on Windows, Linux and Mac that makes it trivially simple to combine these two exposures – assuming they were taken on a tripod and the zoom, focus and direction does not change between shots.  StarStax is tailored to stacking star trails, but it does the same operation that Photoshop (and Image Stacker and StarTrails.de do).

And fortunately you can make it do a little more with almost no extra effort… as in this example. When the first image was taken it was quite dark and required a long exposure to capture foreground details.  Then all the moon images were taken with identical settings using an intervalometer.  It’s interesting to note how the moon darkens and deepens in color as it sinks in the atmosphere.

Project Impact [5_057573-615br]

So how do you create the simple or “stacked” motion images?  Easy.

 And here is the result.

Obviously to create a descending or ascending moon sequence you merely need to combine exposures taken at the appropriate interval. What is that interval? The moon travels roughly its diameter in two minutes. About 2 minutes, 14 seconds to be more precise.  I recommend taking exposures twice or four times as often as that, however and just use every-other or every fourth shot.

Since I took a simple approach to blend the images I also elected to go simple in presentation. Rather than fight the many different colors inherent in urban night scenes, I used Picasa3 to convert to monochrome, crop and frame the combined image – here using an earlier shot than the “Golf Ball on a Tee” shot above.

In the Evening [5_057775+92]

Here is one last example of a descending crescent moon combined using Photoshop. Here I didn’t wait a full moon diameter time between images because it was a crescent moon:

Mamma Glows, Baby Shines

 This also illustrates why taking more frequent exposures gives more creative latitude.