Shooting moonlit landscapes is quite different from shooting using sunlight as your light source. The moon reflects between 3 and 12 percent of light from the sun, so you will be operating in a very low light situation. Some adjustments will need to be made within the exposure triangle (aperture, ISO, and shutter speed) to achieve optimum results.
You will need to set the lens used to the widest aperture possible to keep the shutter speed and ISO to a minimum. Realize that this may not be the optimum setting of the lens used to obtain maximum sharpness (usually for most lenses it is f/8 to f/11) and some depth of field will be lost, so you may want to adjust the ISO and shutter speed accordingly to increase sharpness and depth of field.
It’s recommended to keep the ISO settings low when possible, but with a good quality camera sensor amazing results may still be obtained with up to ISO 3200 and even higher. I prefer to keep the ISO maximum setting at 3200. Lightroom and other post-processing software greatly help with reducing noise that is inherent with higher ISO settings, but it is better to keep the noise down on the original image.
Shutter Speed and How to Avoid Star Trails
Due to the Earth’s rotation, if an exposure is set beyond a certain time frame, the stars will seem to be out of focus and appear as streaks or trails of light. To avoid this you will need to keep your exposure time less than the time that star trails will appear in the photograph.
There is a way to calculate this maximum exposure time, and that is the “500 Rule.” Here is the formula.
For a full-frame sensor, simply divide 500 by the focal length of the lens and that will tell you the maximum shutter speed to avoid star trails.