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I have only been taking pictures for a little over a year now so any help will be great. My problem is I was trying to get the exposure balanced on a night shot of an old barn with the moon rising above it and the best i could get has a lot of noise in it. I think my iso was to high but was the only way i could have a fast enough sutter speed. iso 800 exposure 0"6 s f 2.8 exposure +1 mode "av" white balance automatic my focal point was the bright sky around the moon. Camera was a Canon eos 40d with a Sigma 105mm 2.8 lense. Thank you for any help.

The easiest way is to (spot)meter the darkest and brightest areas of your composition and take the average exposure.
As a rule of thumb, if the difference between the darkest and brightest spots is more than 5 stops / EV (for jpeg) or 9 stops / EV (for RAW), you'll have to choose whether you still want detail in the shadows or the highlights.

Example:
Suppose the moon is 1/125 s @ f/11, iso 100
and the barn measures 8 s @ f/11, iso 100
then the exposure difference is 10 stops, so either the shadows or the highlights are clipped. The average exposure would be 1/4 s @ f/11, iso 100. To show detail in the barn you could go for 1/2 s or even 1 s.

Hopefully my explanation makes sense. Good luck in further efforts!

What are you wanting to do? Do you want the barn exposed more than it is? You can do that by making two exposures and combining them in photoshop or whatever editing program you use.

Thanks for your help ,I guess what I wanted was to be able to balance the exposure better without using layers in Photoshop, Ill have to learn how to use layers.

In order to balance without using digital manipulation, you're going to need a graduated neutral density filter. Treat the moon like you would the sun, the exposure of the moon is about the same as a sunny day, i.e. Sunny 16. (1/ ISO at f.16)

You can get a 2 or more stop graduated filter and use that to darken the sky. Unfortunately, you don't have a clear horizon line, so you could be out of luck on that approach with this particular shot.

Or... don't wait for a pitch black sky. Shoot at dusk, so that the contrast isn't too high. Only problem is that you may have to wait for a year to have the moon in the same position...