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This is my first star trail photograph stacked with StarStaX and can't seem to find out why they are so blurry.

I have a sturdy metal tripod with a cable release and shined a light to focus on the foreground beforehand. The image is at f/4 aperture, 30 second shutter speed, ISO 250, with a 24 mm focal length and manual focus on. Any advice would be helpful and don't be afraid to ask for any other pictures to help me figure this out.

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shined a light to focus on foreground beforehand

If you focused on the foreground then the most likely explanation is that the stars are blurry because they are out of focus, at f/4 the depth of field is not sufficient to contain both the foreground and the stars (which are effectively at "infinity" or as far away as you can get).

I would recommend you try to manually focus on the stars themselves, this is difficult as they are so dim, even with live-view and high ISO settings. The best approach is to attempt to focus as best you can, shoot a short trails exposure, check focus on the rear LCD at maximum magnification, if it's repeat those steps and keep going until you nail the focus.

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  • You could also try using manual focus and focusing to infinity
    – laurencemadill
    May 14, 2015 at 10:44
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    @laurencemadill Very few lenses focus accurately to infinity when set to infinity.
    – chili555
    May 14, 2015 at 12:10
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    If the moon is around, focus on that. Otherwise something far on the horizon could work too.
    – Weboide
    May 14, 2015 at 12:13
  • @chili555 oh ok, I'd never really tried; I have to rely entirely on autofocus because I can't see focus properly when I try to use manual focus
    – laurencemadill
    May 14, 2015 at 16:05
  • Thanks everyone for the advice now if I used a bigger aperture NUMBER with a longer shutter speed would that be easier to focus and/or give me a better outcome or should I just keep it at 4, im looking for a night without the moon for less residual light, and my lens doesnt have a symbol that says infinity like ive seen do I just turn it all the way clockwise .also I did many test shots but didnt even think to check the focus at 100%. ill pay closer attention to these details next time.
    – Seantography
    May 14, 2015 at 17:31

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