I have yet to photograph a volcanic eruption. It is number one on my list of subjects to shoot. This picture is the closest I've come. It is Mt. Arenal in Costa Rica spewing molten boulders in 2010. As they crashed down the mountain side (making amazing sounds), they broke into many pieces which left trails of fire. I shot this from the balcony of my hotel with a 30 second exposure, f/4, and 800 ISO. How did I determine these settings? Trial and error. There is no way to take a light reading in this kind of situation. There is, in essence, no middle gray from which a meter can derive an accurate exposure. I started with the long exposure because I wanted to capture the dendritic trails of light. Then, I assumed since it was dark, I needed a large aperture. At this distance, depth of field wasn't an issue, so I chose the largest aperture on the lens -- f/4. I then varied the ISO until the exposure was correct. I took this with a 24-105mm lens.
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