star trails with camera on tripod

[Taff]

Hi' how long do i gave with a camera on a tripod not to have star trails in the capture Thanks.Taff

[jgs001]

that depends on the focal length of the lens and where in the sky you are pointing. I've got away with 30s at 18mm, pretty much anywhere. Someone on here has a table that shows approx exposure lengths based on lens focal length (35mm equiv).

[Taff]

Thanks John' for the reply.Mark

[themos]

If p is the pixel pitch of your sensor (in microns) and f your optics focal length (in millimetres), the time (in seconds) you have before an equatorial (declination 0) star centre moves to the next pixel is about 14(p/f).

14 comes from (1/1000)*(180/pi)*(3600)*(1/15)

[barkis]

A star will move 15 arc seconds in one second of real time. So point at a fairly bright star, and count off 10 seconds. The star will have moved 150 arc seconds. The perception of this distance to your eye, will depnd on the focal length of the lens you are employing.

With digital slr cameras, it is easy to experiment yourself, with a series of timings using lenses of different focal lengths. Also, as John has said, the trailed lengths are dependent on which part of the sky you are imaging. At the celestial equator, the trails will be longer for a given time. Near the pole, they will be at their shortest.

Ron.

[Taff]

Thanks for your help.Mark

[astro_dt]

Hi Taff

I have some tables on my website which should help you.

They are in the Technical section and you can download a spreadsheet (from the Links page) that allows you to customise the focal lengths to the lenses that you have.

Hope it helps

Danny

[EA2007]

most camera's I have used show trails after 30 secs, however, that is on a the normal view, zoom in on an image anywhere over 20secs and you will see the beginning of trailing.