How to Focus stars?

[mukul]

How do you focus stars while shooting night sky? It is impossible to place focus point on a star @18mm (apsc ) and achieve AF or MF.

Tried by setting the lens in MF mode and rotating the focus ring to the full extent in the hope to achieve infinity. But it did not work. Stars are appearing as tiny perfect circles.

600D, 18-135 1st version

 

[stevelee]

Did you try just manually focusing visually? Just make the stars the smallest dots of light possible. At 18mm you should have a lot of leeway. If they look like small dots over a small range, try right in the middle of that.

The infinity stop allows for different wavelengths including infrared.

 

[neuroanatomist]

Focusing to the smallest points of light in live view works well. Another option is to focus on something in daylight that’s about 7 m / 20 ft away, then mark the position of the focus ring with tape on the barrel. At 18mm f/3.5 on APS-C, that will mean anything from 3 m / 10 ft to infinity is in focus.

 

[snappy604]

haven't tried specifically for this, but for some low light far away stuff you can use live view to aid. Tripod mount, put focus on manual, put on live view, find star and then change your focus wheel until it seems focused and then digitally zoom and fine tune. its way better than your eyes alone.

 

[Don Haines]

I put the camera in live view, let it focus on something far away, and the flip the lens switch to MF.

 

[Hector1970]

A light in the distance would be good enough for the lens you are using. It would be no harm to mark it with Tippex or something so you know where the point is.