Updated: Oct 1
Nightscape photography requires you to switch that camera into manual mode. Not only for exposure but also for focus. Without light in-camera autofocus becomes useless and setting your lens to infinity won't always achieve the crisp sharp results you are looking for.
Focusing in the dark isn't a difficult as it may seem. It begins with switching the camera and lens into manual focus. Next you need to adjust your ISO to somewhere near where it should be for your final images and set your aperture as wide as it will go.
Now point your camera at the brightest star in the sky or some distant bright light if there is one handy and zoom in as far as possible with the LCD. Manually focus your lens until the bright point of light is as small as possible. It can be helpful to have a 10x loupe to get a really close look.
You camera is now in focus. It's a good idea to check the focus point on the lens indicator if there is one to get a rough estimate of where focus is. This can save time in the future by allowing you start near the right place.
The final step is to take an image and zoom in to various parts of it to double check focus. Remember if you move, change camera positions or touch the lens at all it's best to recheck focus. There are few things worse that setting it once and forgetting it only to realize at the end of the night that somewhere along the line your images are no longer sharp. This process take a little practice but will shortly become second nature.
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