Regarding long exposure star trail photography with camera lenses, remember that in a lot of climates moisture will condense on the lens surface as the temerature drops to dew point. Consult Sky and Telescope magazine archives for articles on this subject. The object is to keep your lens surface just above the dew point so it will stay moisture free. When the objective is to image faint stars, the aperture settings and focal settings are critical. Significant improvement will likely occur when optimal settings are used.
Experimentation pays dividends.
If no time to experiment, a rough guideline is to reduce apperture 1 stop from wide open. For the curious, the circle of confusion will be reduced as the aperture is closed more than optimal for the above purposes until diffraction effects about the aperture edges add disproportionate degradation. Since the light of the sun hits the moons surface almost straight on, you won't have the shadows that bring out surface detail like mountains and craters. Half and quarter moons are much more interesting because you can see more of the features of the terrain. A must for any star geek.