Startrails – Software

Star trails, image credit: Ralph Clements
Star trails, image credit: Ralph Clements

Star trail images are beautiful to look at and they are captivating because they make time visible. These images can be made either by exposing one single image over a very long period or by taking many shorter exposures and combine them afterwards. Digital cameras deliver images as electronic files, making combining very easy – particularly with software that does all the combining work automatically. One of these software tools is the program Startrails. This software has been developed by Achim Schaller, and he did an outstanding job. Not only is his software really easy to handle, but it comes with powerful features – and it is free. Startrails can be downloaded at Achim’s website.

The Program

Startrails is designed to automate star trail image processing by combining a series of input files into one final image. It is Microsoft Windows based and runs on Windows XP and later versions. Microsoft .NET framework has to be installed on the computer. Simplicity is a key attribute that sticks out immediately. Only 6 buttons maneuver through all functions of this software. It processes input files in JPEG, TIFF and BMP format and stores results also in these formats.

Processing Images with Startrails

Processing star trail images consist of the following steps:
  • Selecting images
    Select all star trail images at your HD or memory card. It is recommended to go through every single image and unselect the ones that have flaws. Air traffic or blinding lights of a passing car can sometimes spoil a good series. Taking out one or two sequential images is virtually not noticeable in the final star trail image but improves the overall appearance considerably. Sometimes however, “disturbances” are wanted; the firework of a meteor or the bright reflection trail by the International Space Station (ISS) are usually considered an upgrade to most images.
  • Dark frames
    Startrails software handles dark frames, or Darks for short. Darks are taken with the lid on the camera lens. This way only noise that is caused by the CCD chip is recorded. Noise in the actual images is random, but each CCD has a particular noise pattern which, can be subtracted from the final image pixels. This step improves the image quality significantly. If more than one Dark is available, Startrails averages them. Using Darks is highly recommended when images are taken with high ISO speeds.
  • Averaging
    Averaging images improves the signal to noise ratio. As a result it reduces (random) noise of the images and increases brightness (luminosity) of the stars. The averaged image becomes brighter and is blended into the resulting image.
  • Run process
    No interaction is required during the run. After it finished, results can be saved in JPG, TIFF or BMP file format.

Startrails Software by Achim Schaller

Note: Images can often be improved by post processing. Stars can be made brighter, background sky can be darkened. Good image processing software is available from many companies or organizations. Photoshop is probably the most common software for astrophotography, but freeware like GIMP performs also quite well.

Time Lapse Movies

Startrails has another powerful feature: it can create time lapse movies. Of course, it can create any kind of time lapse movies, not just astronomy movies. The output format is AVI with the following possible compressions:
Full Frames (uncompressed), Microsoft RLE, Microsoft Video1, Microsoft H.263 Video Codec, Microsoft H.261 Video Codec, Indeo® 5.10, Cinepack codec by Radius, Logitech Video (I420), Intel Indeo Video R3.2, Intel Indeo Video 4.5, Intel IYUV Codec.
Startrails converts the image input resolution during compilation into the wanted AVI screen size. The same is the case with the desired frame rate (fps) and some compression settings to set the streaming speed (kbps).


I’m often asked the question:  What do I need to take star trail photos? Well, the answer is: not much. A camera with remote capability and a solid tripod is basically all that is needed. The camera should make JPEG, TIFF or BMP images. The tripod has to hold the camera steady, even when light wind gusts occur.


DLSR cameras are perfect, but simple point-and shoot cameras may work as well. Even smart phone cameras may be suited. There are no real strong demands on camera optics; it simply depends on what image quality level you desire. The better the optics the better the resulting images will be. The faster the lens (1/f) the less ISO speed is needed and with that, lesser noise is introduced. Other things to consider:
  • Memory Size
    The memory card must offer sufficient space to hold the truly huge amount of data that will be stored during the shooting session.
  • Intervalometer
  • Wide Angle Lens
    Star trail photos look better with many stars on the image. Foreground objects are improving visual image balance. Most photographers use their widest angle lens (or zoom setting) for these photos to capture as many stars as possible for best effects.
  • Manual Focus
    Most digital cameras have great difficulties focusing on stars when the rest of the image is extremely dark. Manual focus capability is required for star trail photography; any auto focus feature on camera or lens has to be off.


Startrails is a powerful, yet easy to use all-in-one program for star trail imaging. It allows to create time laps movies in AVI format. Startrails is great freeware and well suited for beginners and advanced amateur photographers.

Send us your star trail photos. Tell us where and how you made them.

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