I have written about night photography before. In those blogs, I wrote about composition and focus and so forth. Today I am going to talk about shutter speeds. How do you calculate what shutter speed you should use? Of course, I cannot talk about what shutter speed to use before talking about how you want the image to look. Let me start by showing you two images from the same spot taken on the same night.
Which image do you prefer? One image was taken with a long shutter speed while the other was taken with a short-ish shutter speed. Because of the rotation of the earth, a long shutter speed shows the motion, hence the star trails of the first image. The short-ish shutter speeds leave the stars sharply in focus. So let's start there.
The wider field of view your lens has the faster shutter speed is needed to get the stars sharp. I am talking about getting your shot in one image rather than using stacking techniques. Try to keep your shutter speed at 30 seconds or below. Use your lens' fastest aperture. Jack up your ISO to get your exposure right.
For the long exposure (star trails) you can leave your shutter open for a long time. I mean a really long time, like half an hour or longer. If I recall correctly, this image was exposed for 50 minutes. But there is a problem. The camera's light meter does not work beyond 30 seconds. So how do you know that this image needed 50 minutes versus 20 minutes, for example?
Set the camera's shutter on 30 seconds. Now play with your ISO until you have the correct exposure. Since it is dark your ISO will be very high. Once you know what the correct exposure is we can now change how we get that exposure. Half your ISO but double your shutter speed. Keep doing that until you have a low ISO. You will have to double the shutter speed in your head because your camera does not have a measured setting beyond 30 seconds. Place your shutter speed in bulb mode. Use a remote shutter release so that you can lock it in the depressed position. Now use your watch or your phone's countdown to measure out the calculated time. See that was easy.
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