The Rule of 600

As discussed in detail in my article on meteor shower photography, the quickest way to determine the longest exposure that is possible for any given focal length lens, without the stars streaking, is to divide that focal length into 600. (This is the formula for 35mm. Larger formats are laxer, smaller formats more unforgiving). Since the 35mm focal length equivalent for the 14mm lens that I was using on the D60 is 22mm, I used a 30 second exposure (600/22=27 seconds. Close enough).

Of course if I was willing to accept the stars turning into trails I could have done a much longer exposure. But my goal was to experiment with trying to achieve a natural appearance that blends the best of daylight landscape photography with a "night look", with stars playing a dominant role.

SOURCE

technorati tags:photography, focal-lenght, 600-rule, long-exposure