Astrophotography

Astrophotography Tutorial – Step 3 : Star Trails

Intro

Now that we have a bunch of images we can start to test out a few techniques, we’ll use the images we have captured to:

  • Generate star trails
  • Create a basic time lapse video
  • Combine both the above

Generating Star Trails

To create the trails you can use

I’ll be using starstax to generate the trail stills and imagej to generate a video (although startrails is capable of doing both)

To generate a still image showing the star movement:

  • First go through each frame in the sequence and make sure you don’t have any planes / satellites in any of them, if you do they’ll need to be cloned out.  I generally generate the trails as described below and watch the output as it goes through the images, if I see a artifact like a plane pop up I stop the process, check the image highlighted on the left and correct it in lightroom.  Once I have the image as I want it  it i re-export just that image and go back to Starstax and rinse and repeat.
  • Open Starstax
  • Click open images
  • Select the images you have exported during post processing
  • Open the right hand tool area by clicking on the preferences icon
  • You can experiment with these settings but I used  blending mode: Gap Filling, and comet mode
  • If you want to generate a movie from these click “Save after each step” then start processing by hitting the button on the top toolbar

Here’s an example of the still I ended up with:

Trails Still

Making Videos From Image Sequences

IF you’ve been following the tutorial you should have 2 distinct image sequences, the first is the output of post processing which so far we have used an input into the star trail generation process and the 2nd is the star trail images we have just generated (if you selected save after each step).

We are now going to turn those sequences into videos.  To do this I used ImageJ which is a free image editing suite.  This will turn out sequence of images into a video, there are a bunch of other tools you can use here too.

To generate video from stills:

  • Open ImageJ
  • Select File -> Import -> Image Sequence
  • Navigate to the directory of your images sequence (try to make sure that only those are the only files in that directory).  You can use your output from post processing for a normal time lapse or the output from starstax for star trials.
  • Select the first file in the list and click open
  • You can resist the images if you want to speed tbe process or keep the file sizes down
  • Hit ok and wait
  • Once complete you’ll see a preview window with your video, review it and make sure your happy
  • Click File -> Save As -> Avi to save the video

Here’s what I ended up with

I made a standard time lapse but there was a lot of star flicker (dull stars were in some images but not others) so I didn’t post it.  I’m not 100% sure why this happened, I assume it was because light conditions were changing throughout the 90 minutes I was shooting for, flood lights turning on / off etc

Star Trails:

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s