500 Rule Calculator is a useful tool for photographers who need to calculate proper exposure time for star photography and avoiding unnecessary light trails.
The calculator uses the 500 Rule, and allows the user to select their cameras crop factor, so this app will work for photographers shooting full frame, general APS-C (Nikon, Pentax, etc.), or Canon APS-C. The app also allows the user to select from a wide variety of standard focal lengths, and get the time in seconds for the right shot.
The app also includes a countdown timer for use in star photography or any long exposure photography situation, ranging from zero seconds all the way up to 15 minute (900 second) exposure time.