To infinity or beyond?

I was at Lake Powell last week and tried doing some star pictures. One thing I encountered was where to focus. Looking through the viewfinder pointed at the sky, even when it's a 2.8 lens, gave me nothing to focus on. So I changed to manual focus. But then the question, do I set the focus scale at infinity or do I set it to beyond infinity? I've never had to deal with this before so I've never thought about it, what is the correct setting?

Here are a few of my results. The first picture is the EF-S 17-55 f2.8 lens, f2.8, 1600 ISO, 1 minute exposure to minimize star trails. The second photo is the same lens, f8.0, 100 ISO, 10 minute exposure to maximize star trails. The glow is light from Page, AZ, about 10 miles away. Both pictures taken around 2am. I adjusted levels and color in ACR and Elements 5.0, used the dust and scratches filter in Elements and then removed noise with Noiseware community edition, which is why there is no EXIF data, the freeware removes it.

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Lenses go to "infinity and beyond" to allow for thermal expansion/contraction and for IR. Typically you'd set it at infinity as marked, not beyond... But even this isn't necessarily a given. Point the camera at the stars and focus until the stars are sharp.

Thanks for the reply DN. The reason I asked is that the sky was so dark that when I looked through the viewfinder the stars were just small points of light on a black background. When I adjusted the focus I really couldn't see any change in the viewfinder unless it was grossly out of focus. So I just set the focus ring to infinity and shot.

When I downloaded to the computer I could see that the series of star traces like the second pic I posted were not quite in focus, the star tracks are kind of wide instead of being narrow lines. But like I said, I couldn't see fine focus through the viewfinder.

It might be a good idea to focus on infinity (meaning a couple of miles away or more) when you can see well and make a mark on the lens.

-js

#6, that's a good idea.

Once you get the focus set by focusing on a high contrast lighted object at infinity (or shooting test pics and zooming to inspect), tape your focus ring in place and leave it taped for duration.

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