[alamo5000]

I am hoping someone can give me a basic formula for getting good night shots where the stars won't be trails.

I am shooting witha K5 and any of the DA Limited primes... probably the 15mm.

[Medium FormatPro]

Well astronomy and physics wise it also depends upon which stars one is photographing and also ones latitude where one is taking the photograph. But generally, anything above 20 second should limit any star trails with that lens

[VisualDarkness]

I think it was something like 400/focal lenght=Max Shutterspeed.

[russell2pi]

A common rule of thumb for shutter speed is 600 seconds divided by the focal length of the lens. That depends though in which direction you're looking and how much elongation you can tolerate, but it will give you a good starting point. It doesn't take long to make an exposure, playback and zoom in to check.

Wide open or nearly so and ISO 800-3200 - again trial and error. Stars vary hugely in brightness so it's a tradeoff between blowing out the bright ones (and losing their color) and making the dim ones visible (and noise of course).

[drg0012]

Usually for me, I keep the lens wide open, kick up the iso a bit (800 or so), and keep the exposure under 20 seconds. You can make adjustments from there, but that's usually where I start.

Good luck!

[alamo5000]

wow. so many quick responses! Thanks guys!

I am going to try and do some night shots in the near future if its clear.... it will be my first attempt at it.

[VisualDarkness]

A common rule of thumb for shutter speed is 600 seconds divided by the focal length of the lens. That depends though in which direction you're looking and how much elongation you can tolerate, but it will give you a good starting point. It doesn't take long to make an exposure, playback and zoom in to check.

Wide open or nearly so and ISO 800-3200 - again trial and error. Stars vary hugely in brightness so it's a tradeoff between blowing out the bright ones (and losing their color) and making the dim ones visible (and noise of course).

Isn't that for fullframe and 400 for aps-c?

[DeadJohn]

P.S. As you get more advanced, you can take several shorter exposures to avoid trails, then stack them with free software like Deep Sky Stacker to increase brightness, enhance nebulosity, and reduce noise.

[alamo5000]

nebulosity. I learned a new word today. I can only imagine what it means exactly

[steve1307]

If you point towards the celestial pole (north in northern hemisphere of course) the stars will give shorter trails so you can shoot slightly longer.
Pointing directly east or west the motion of the stars relative to you is faster so the trails will be longer with the same shutter speed. Hope that made sense.
.....or you could use astrotracer with O-GPS1 and a K-5

[Na Horuk]

I think there were a couple threads on this already btw, so maybe they have a tutorial or two. The 15mm would be good because you can have a long exposure and the stars still won't have trails (because it is a wide angle), but at f4 it might be a little slow. On the other hand, you can bump up the ISO pretty high with modern DSLRs. Just use a good tripod, make sure there are no vibrations. Use a 2 sec timer or remote control. Shoot in M mode, keep the aperture wide and use as long a shutter as you can tolerate, then adjust ISO accordingly.