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Ramblings of an Amateur Photographer

500 Rule

500 Rule This week over on The Snake Tips I critiqued an image that someone sent in about photographing the stars. In that post I talked about when the stars will start appear to "move or streak" while taking night time shots. Before you take the shot you can use the 500 Rule to approximate the maximum tile you can have your shutter open. It's also known as the 600 Rule and either can be used, 500 is a little more conservative. Remember it's just a starting point. Broken down you divid 500 by the "true" focal distance of your lens. The true focal length is the length after the crop sensor (Canon crop factor is 1.6 & Nikon {and Fuji} is 1.5). So for my 8mm Rokinon fisheye on my Fuji I can keep the shutter open for a max of 42 seconds before I start to see streaking in the stars. Is there math around this? Sure there is. Do you really want to see it? If so go to Star Circle Academy.   I found it interesting, but I am a bit of a math geek.