Imaging Star Trails

[groberts]

Another clear sky last night (hooray) so, so a change, I thought I'd take a stab at imaging a star trail.  

Canon 700D 18mm - 55mm lens set at 18mm, f4, ISO100 for 20 minutes on a tripod.  The result was (and now I think about perhaps not) a surprise.  Yes I got good trails but the sky which was dark (OK a bit of light pollution) was too light / overexposed making some of the rails difficult to see.  With the ISO at 100 I can't reduce this any further, so what am I doing worn / how do I get the sky darker, other than post processing perhaps?   

[Leveye]

You should use an intervelometer and take 2-3 minute  exposures with as little time in between as possible over say a 2-4 hour time period and then stack those using something like StarStax. Much cleaner and better looking end result.

[JamesF]

I've used this in the past: http://www.startrails.de/

Seems to do a nice job of merging all the separate exposures.

James

[bobmoss]

Don't forget that you can use a smaller aperture (bigger F number) to gather less light. So often we are used to using as bigger aperture as possible to get as much light as possible.

[szymon]

You have three controls -- aperture, shutter speed and ISO. If you're using the shutter speed to get long trails (so must have a long exposure), you need to use both the others to compensate. Stop the lens up, try f/8 first and more if necessary.

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