Tips for star photography?

theoldsmithy

Hall of Famer
Location
Cheshire, England
Name
Martin Connolly
Hi everyone, last night was wonderfully clear and starry. The Milky Way was showing up nicely so I thought I'd attempt some photos. I got out the tripod, set the X-E1 up with:
- image stabilisation off
- ISO 6400
- aperture wide open (f3.5 on the 16-50 zoom at wide angle)
- 15 second exposure
- 2 second timer
- manually focused to infinity

The exposures looked pretty good but all the stars showed up as fuzzy blobs instead of sharp dots of light. I had assumed that focusing to infinity (or as far out as I could manage anyway) would do the trick. I wasn't able to check the focus in the viewfinder - it just didn't show me anything except a black screen.
Any ideas for what might have gone wrong?

Thanks
 
One thumb rule is to divide 600/"equivalent focal length" to set shutter speed to avoid smeary stars. If you're using a 50mm lens on full frame then 600/50 = 12secs. That would be the maximum time you can leave the shutter open without stars moving from position (or actually the earth rotating) enough to give you a blurry image. If using an apsc sensor use the 35mm equiv focal length.

Of course once you go past this simple exercise, things start to get really crazy like the LL article in the previous comment.

edit - Oh this is a really good video talking about the basics -
 
From my experience, f3.5 isn't really enough to get the ISO and shutter speeds down to where they need to be. I generally wound up around f2 to make it work out, both on the X100 and the XT1. With stars, little tiny pin pricks of light, just the noise of ISO6400 would probably render them a little blobby anyway, I would think. Again, I generally kept it at 3200 or under, from what I remember.
 
This one , taken from my back door was 15 sec at f2.8 ISO 2000. I found the focus (manual) scale to be accurate on my GH3. (12-35 f2.8) set to 12mm. 24mm FF
The fuzzy blob lower right of center is the galaxy Andromeda. Image was subject to heavy processing, but i'm happy with the result.

15114709579_931cb6ee9c_b.jpg
untitled-1030100 by sucofni, on Flickr
 
Its difficult to get a balance between "right for the night" and no star trails. Its instinct to open up the aperture but I am intending to try stopping down a bit more useful for a blobless shot, with ISO as high as I can manage, and shutter no more than 10 secs or so. My experiments thus far with apertures of f/2 and f/2.8 have been quite blobby. I want to get pinpricks of light, instead, and normally f/16 onwards get starburst effects in night shots, why not with shooting the stars. I've never shot my K5 at a really high ISO but I reckon with a black night, it probably doesnt matter that much about noise.
 
This one , taken from my back door was 15 sec at f2.8 ISO 2000. I found the focus (manual) scale to be accurate on my GH3. (12-35 f2.8) set to 12mm. 24mm FF
The fuzzy blob lower right of center is the galaxy Andromeda. Image was subject to heavy processing, but i'm happy with the result.

The dense star cluster on the lower left is the "Double Cluster". Not a bad shot.
 
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