Aperture for Stars? - other questions too.

Going to try a few landscapes in the near future and was going to be using my Sigma 30mm F1.4 as it is the fastest, widest lens I own.

Was wondering what aperture I should use. Should I open it right up to F1.4 or stop down a bit.

Also, I'm thinking 20 seconds or so to avoid star trails. Does that sound right? What about iso? 1600, 3200? Lower? Using a canon 60d with long exposure noise reduction turned on.

Thanks in advance,
Corey

Hardcore wrote in post #11711894
Going to try a few landscapes in the near future and was going to be using my Sigma 30mm F1.4 as it is the fastest, widest lens I own.

Was wondering what aperture I should use. Should I open it right up to F1.4 or stop down a bit.

Also, I'm thinking 20 seconds or so to avoid star trails. Does that sound right? What about iso? 1600, 3200? Lower? Using a canon 60d with long exposure noise reduction turned on.

Thanks in advance,
Corey

All of the night shots that I've done have been with the aperture wide open. The Stars are just points of light, so shouldn't have sharpness issues. Depending on what other stuff you have in the foreground, you may want to experiment. I wouldn't go over ISO 800, as you'll still get noise. You should get plenty of light with that lens.

Even F1.4 has ALLOT of curvature to the lens. I'd stop down to 2.5 to 3.2 to get the field/corners flatter. Depends how picky you are. Wide open could also cause the stars to bloat or CA.

High ISO if your camera can handle it but 1600 is fine. @ 30mm you can get 30secs I think (sorry been a while since I used that wide of a lens). Take equal number of lights with darks (lens cap on for same exposure & camera settings. Oh and turn the long noise reducs OFF, you'll use the darks to cancel out the noise.

jsigone wrote in post #11712945
Even F1.4 has ALLOT of curvature to the lens. I'd stop down to 2.5 to 3.2 to get the field/corners flatter. Depends how picky you are. Wide open could also cause the stars to bloat or CA.

High ISO if your camera can handle it but 1600 is fine. @ 30mm you can get 30secs I think (sorry been a while since I used that wide of a lens). Take equal number of lights with darks (lens cap on for same exposure & camera settings. Oh and turn the long noise reducs OFF, you'll use the darks to cancel out the noise.

Isn't that what long exposure noise reduction does? Ya I was thinking stopping down might help a bit but wasn't sure.

yah but it adds its own type of noise. Much cleaner to cancel it out with darks. 30-100% darks to light ratio works fine, closer to 100% matching gets better details.

20 seconds might give you star trails with that setup.

The general rule of thumb is: 500 / (focal length * crop factor)

If 20 seconds is too long, try 10 seconds.