How long should a shutter go for a star trails picture?

How long should a shutter go for a star trails picture?





I saw those star trails picture where the trails go like a circle. How long they were done?





Thanks!|||You need about 2 hours for circles, but this will generate a lot of 'noise' as the sensor gets hot over such a long exposure.





Better to take 30sec-1min exposures and stack them together using software like Startrails application (free);


http://www.startrails.de/html/software.h鈥?/a>





this also avoids problems of the camera battery running out during the exposure, as you can change it out between shots.





This one I did was 129 30 sec exposures taken 10 secs apart;


http://www.flickr.com/photos/deepbluepho鈥?/a>|||The answer is for as long as possible. You must close the shutter well before it gets light though. At this time of year the best you could hope for is about 6 hours, in the northern hemisphere. Longer as you get into the winter.|||At least 30 minutes for a worthwhile effect. Sensor noise is an issue as it heats up; best thing is to use a film SLR as it is not an issue with film.|||depends how much of a trail you want... some people take many short shots and then merge them...





the number of photos will depend on the longest shutter speed you have...|||In range of 1800 secs... give a take 100 secs...