StarTrails: Quick Guide

Earth rotates.  As it does, stars visible in a night sky change position relevant to the Earth's surface.  The rotation happens a great deal faster than one would expect, and even with 30 second exposure of the night sky the star tracking becomes visible.  Outlined below is a basic technique that allows to capture a series of images of the night sky.  Later, combined, they reveal starTrails.

  1. Pick a location with absence of strong artificial light source. Best is to find something way outside the city lights, highways (headlights), etc.
  2. Best to do it on a cloudless and moonless part of the night (or new moon)
  3. Steady tripod is a must. Point your camera at an angle from south or north location: you'll get more pronounced trails and curvature will be more visible. So you'll get better results in shorter time period.
  4. Set your lens to a short focal length available (I used 50mm prime for the photo featured above, but also got good results with 18mm). Focus to infinity, then pull back just a tad. I find I get the best focus if I'm not at the max.
  5. Finally, set your camera on manual, and shoot away. Choose largest aperture (anything 2.8 or more is recommended). I set my iso to 400 (good compromise for noise on film vs sensitivity - if you don't have a lens that gives you big aperture e.g. f/3.5 or less - up your iso a bit ), White Balance usually set to fluorescent (preserves "natural" color in my opinion), unless you want to modify it manually, but even with batch processing I usually end up with hundreds of images, so it's a pain :/
  6. I keep exposure time usually to 30 seconds. anything more, and trails become visible on current exposure, so once images are combined, it looks messy
  7. It's good to use some type of timer for continuous lapse shots. I use a timer on the battery grip, but also have used a cheaper solution: standard shutter release cable and just taped down /lock the shutter button so camera keeps firing continuously.
  8. Finally, processing. The shot above is HDR of 11 images, each taken at 5 min. interval. That what gives it that dots effect (there's a 5 min lapse between each gap over 2 hr period). But you can also use many fantastic *free* apps out there, such as IRIS or starTrails to combine/stack images. Finally, you can also use each image as frame and make an animation. search "timelapse photography" on youTube. There's amazing work out there.
p.s. here's the "continuous" image stack of the same shoot combined in starTrails. I wasn't happy with the results, but here it is for comparison

Animating Star Trails:
With captured images, you can also create an animation to demonstrate star movement.  This is an example of a movie made with frames from the same shoot.  

I use Adobe CS4 for post-processing and to compile animation. To create the animation , do the following:
  1. Open Adobe Bridge
  2. Select all files from your shoot
  3. Double click on any one of the images to open series in Photoshop
  4. Do "select all" and perform post-edits to your preference (e.g. WB tweaks, noise reduction, crops for wide screen format, etc..).
  5. Select "save as" and convert modified RAWs to JPEGs
 Animation Process in Photoshop:
  1. Open Photoshop
  2. File > Open > Select 1st image in the series > check "Image Sequence" option box > click Open (FYI, for this to work, all images must be sequentially named, any gaps in the series will pose a problem)
  3. Select frame rate. Usually anywhere from 24 to 30 should be ok. The one above is at 26fps (or photos per second)
  4. Preview your animation, and if you're happy with it go to File > Export > Render as video
  5. Select video format and tweak the options to your taste.  The example video was set at 26fps and contains total of 249 exposures.

And that's all there's to it (:  By the way, if you don't have photoshop or any other video compilation application, you can use StarTrails software. It's free, and it does both: stacking and video.  Clear skies and happy shooting (:

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