how to get good star trails?

[Muskydave22]

how long does your shutter need to be open in order to get good star trails? and what are good general aperature and iso settings for trying to get good star trails?

dave

[Trainboy]

Well, I'd say 10+ minutes, but that's just when they look awesome.

[Kevin]

When I do star trails I tend to expose anywhere from 120 seconds (2 minutes) to 240 seconds (4 minutes). As you increase exposure time you will increase the number of stars, brighter stars expose quicker than dimmer stars. If you increase exposure times much beyond 5 minutes you may start seeing hot pixels, which you can clone out providing there are not too many.You can take as many exposures as you like depending on the length of star arc you want, but you don't have to use them all if you change your mind on your composition. I usually shoot to achieve between 60 to 90 minutes of earths rotation. I use Russell Brown's Stack-a-Matic to stack my exposures either raw or TIFF. I usually PP all my file through ACR to adjust color temp and do all PP in ACR before saving as a TIFF. Stack-a-Matic loads from Bridge and loads the final stack into CS4.

Here is the link to Stack-a-Matic tutorial, which just happens to be one of my images. Here is the Russell Brown main page http://av.adobe.com/russellbrown/NewStackAMatic_SM.mov and the Russell Brown Show http://www.russellbrown.com/tips_tech.html. The tutorial is called "Combining Multiple Exposures with Dr. Brown's Stack-A-Matic" most of his scripts are free, including this one.

[Adrena1in]

As you increase exposure time you will increase the number of stars

That's true up to a certain point, but because the stars are constantly moving, the really dim ones will never show up on the sensor no matter how long you expose for.

Personally I stick with 30s exposures, ISO 800 or 1600, aperture wide open or perhaps stopped down a couple, which is ample to capture lots of stars. (First of all I take one or two test exposures with various settings, to see which looks best, then stick with that setting.) I then put the camera into burst mode, turn off mirror-lockup, lock the remote shutter down and go indoors for half an hour or an hour.

Once I'm done, I use Startrails software to combine all the images, or I load them into Adobe Premier Elements and make a timelapse movie.

[TylerCP]

Or if you want to do one long exposure, longer than an hour, its also cool.
ISO 400 with F/5.6 or 8 works great.

Seeing as the stars are so far you can leave the shutter open for a long time as one star doesn't stay on one pixel for so long so it won't overexpose.

[Sorarse]

Seeing as the stars are so far you can leave the shutter open for a long time as one star doesn't stay on one pixel for so long so it won't overexpose.

That may possibly be, but if there is any light pollution in the sky, long single exposures will end up with a bright, strangely coloured sky, which doesn't look very realistic.

[TylerCP]

That may possibly be, but if there is any light pollution in the sky, long single exposures will end up with a bright, strangely coloured sky, which doesn't look very realistic.

True, but if you are far enough away from any city/house/town and there is no other light sources then that rule applies.