Help with star trails shot

Hi, I took this photo several months ago and just got around to asking about it. I read some things on here about how to take star trail shots and tried it but it turned out poorly. I thought I did what most people said to do, low ISO and aperture fairly open. I guess my question is how do I know how to get the best exposure? Is it just a guess to avoid overexposure or is there something else I should do?

F4.5
ISO 200
Exposure 1574 seconds

You're probably better off doing a bunch of shorter exposures then using a program like Startrails to stack them all.

Link to Startrails program herehttp://startrails.de/

Here's a shot I took at ISO 200 F/4 30 seconds each for a total of 56 mins to give you an idea on what you can do when you use the Startrails program.

Beautiful shot. Do you just guess the exposure or try multiple shots?

little late to explain this fun stuff, but try reading some of this for now. good luck.

http://www.danheller.c​om/star-trails.html

http://www.weatherscap​es.com …astronomy&page=​startrails

How dark were your skies? In order to do a 25 minute star trail you need pitch black skies. The darkest skies on the east coast still get pretty light after a while, so you likely are better off taking ~5 minute exposures. Stop your lens down more, shoot in the f/8 or slower area, the stars are brighter than the skyglow so stopping it down will keep the skyglow down a lot.

Another tip, don't get a perfect focus, slightly out of focus stars show up larger and make larger trails that are easier to see.

Some good reading :
http://www.fredmiranda​.com/forum/topic/72576​9/0
http://www.brighthub.c​om …raphy/articles/​42817.aspx