>I am new poster,just beginning to take pictures with a D5100
>1st tried night shots during Geminid meteor shower, no meteors
>and had a hard time w/ focus

I use LiveView and zoom in to a bright star to adjust the focus until the star is a pinpoint. I've also used my tablet with LiveView to get a larger picture to focus with.

I used a Sigma 4.5mm lens for quite a few of my meteor shots and it performed well, including having a true infinity focus mark on the lens.