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.
- Pick a location with absence of strong artificial light source. Best is to find something way outside the city lights, highways (headlights), etc.
- Best to do it on a cloudless and moonless part of the night (or new moon)
- 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.
- 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.
- 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 :/
- 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
- 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.
- 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.
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:
post-processing
post-processing
- Open Adobe Bridge
- Select all files from your shoot
- Double click on any one of the images to open series in Photoshop
- Do "select all" and perform post-edits to your preference (e.g. WB tweaks, noise reduction, crops for wide screen format, etc..).
- Select "save as" and convert modified RAWs to JPEGs
Animation Process in Photoshop:
- Open Photoshop
- 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)
- Select frame rate. Usually anywhere from 24 to 30 should be ok. The one above is at 26fps (or photos per second)
- Preview your animation, and if you're happy with it go to File > Export > Render as video
- 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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