I've tried live view but never with a loupe. I have a hashtag mark on my lens barrel from prefocusing to infinity during the day time, well beyond the infinity mark on the barrel it's self. I now shot in the F/4 range as it seems to be sharper than F/2.8 which I used before. As long as the stars are pin points in the middle of my image I'm happy. At 20 seconds you can see the outside of the image the stars start to elongate, at 25 seconds they all start to get longer when I'm shooting at 16mm.
Nikonian72 wrote:
To pre-focus, are you using Live View at max magnification, with a loupe? Best way to get your stars tack sharp.