Astrophotography

Astrophotography Tutorial Step 4 : Advanced Lapses

Intro

When creating time lapses there are a number of issues that can crop up – for example say you are shooting over the course of a few hours in daylight when the light levels change, you will want to adjust different parts of the sequence in different ways.  If you do this manually you need to slowly introduce these changes incrementally which isn’t really practical.  You might also want to use if for creative reasons too, say to slowly zoom over the time lapse.  There is equipment that can help, you can get zoom machine, sliders / rotators that you can program ahead of time to add another dimension to your lapses, I can’t really speak to those but its possible to get a similar effect using software.

Dynamic Lapses

There are a few tools that can help with this but I’ve used LRTimelapse with some pretty good results.  Since this is basically a hack on Lightroom it means you don’t need to learn to edit your shots in a different software package.  The goal here is to load the sequence into LRTimelapse, define keyframes, edit the images in lightroom and then let LRTimelapse slowly introduce those changes over the course of the sequence.  So say you have a 100 shot sequence and you put a clarify +100 on the last image, LRTImelapse will slowly increase the clarity by +1 on each consecutive image so the change is a gradual one that doesn’t jar the viewer.

There are some really impressive tutorials on the LRTimelapse site above that cover normal time lapses but there are some things we can do above an beyond what we have already done using the image sequence we have been playing with in these tutorials.  One possibility is to create vortex startrails by zooming out image as we stack creating the images below

If you interested in how this is done you can check the tutorial I followed here (it used an older version of LRTimelapse but combined with the basic tutorial from LRTimelapse itslef everything should be apparent).  You will need to fix the foreground after you are done though, I did this using GIMP by taking the foreground from one of images in the sequence I liked the most and then overlaying it on the final result.

Heres what I had before the foreground overlay:

Vortex Trails with no foreground overlay And after: Final Vortex with replaced foreground

To separate the foreground from the image I found one the had the tree well lit from my neighbors flood light, opened it in GIMP, right clicked on the layer and added an alpha channel then very roughly erased the sky on the top of the image. I then used the color select tool to select the darker background and deleted it. This last step was repeated a bunch of times until I happy most of the background was gone. I then deleted the smaller branches on the right leaving just the green leaves. There are a bunch of ways to do this depending on the image itself but this method generally only takes a minute or two and gives good results on night sky pictures.

This left me with:

TreesOnly

which is not perfect but good enough for what we want to use it for.  Its then a case of adding the this image as a layer to the final trail image above and lining everything up correctly.  You might want to slightly scale up the foreground image if needed to make sure you cover all the blurry bits.  Thats it – you’re done.

You can also use the intermediate images created above to put together some more complex time lapses.  Using the output from LRTimelapse and lightroom you can make a time lapse that starts focused on the sky and slowly pulls back:

You can also use the output from each step of Starstax above to do the same with vortex trails.  In this case you will need to deal with the blurry / streaky foreground as it comes into the frame.  One option is to overlay the final foreground over each frame of the image giving you a kind of 2.5d time lapse along the lines of the following:

Both these time lapses were created using ImageJ as in the previous tutorial. To overlay the foreground I used expression encoder on windows – there isn’t really a platform independent tool that can easily do this that I could find.

You are only really limited here by your imagination, please let me know what you create.

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