500 RULE for Astrophotography
As the Earth spins, stars become blurry or turn into trails if your exposure is too long. To capture sharp stars, use the ‘500 Rule’. Divide 500 by your focal length to get the longest shutter speed. At 18mm, that’s 500/18 = 28 secs. The wider your lens, the longer your exposure can be, great for getting more light on your sensor! On Thomas’s ultra wide-angle full-frame EF 11-24mm f/4l USM lens he could shoot at 500/11 = 45 secs.