600 Rule Calculator App – Download on the App Store

My third photography app, 600 Rule Calculator, is now available on the App Store!

I’m fascinated by star trail photography and also shooting the Milky Way. One way to calculate exposure times is by using the 500 Rule. Another way uses what’s called the 600 Rule to calculate exposure times. This is another method to try to have star trails in your shot, or be able to keep the stars sharp, with little or no trails.

But it can be a pain to do calculations, especially when it’s cold and dark, and you’re worried about your gear and getting the shot. It’s easy to make mistakes in the calculations, even if the 600 Rule formula isn’t too hard. But you have to remember it, and also how to take into account crop sensor factor (and what the factor is!) if you’re not shooting full frame.

600 Rule Calculator is the result.

600 Rule app icon 1024 x 1024 alpha


This app is useful for photographers wanting to know what exposure time to set for star photography (or astrophotography) using the 600 Rule formula. This is essentially the same as the 500 Rule, but uses a (very!) slightly different calculation.

The app also takes into account whether or not the user is shooting full frame, general APS-C (1.5 crop factor), or Canon APS-C (1.6 crop factor), and standard focal lengths. The 600 Rule Calculator gives the exposure time in seconds.

The calculator built into the app is easy to use and has 2 input factors needed from the user – focal length and crop factor.

600 Rule iPhone 7 calculator screenshot

Then if you’d like, switch to the timer screen and set the calculated time if you’d like to countdown, or you can use the timer screen if setting really long exposures. This timer counts down in seconds from 900 seconds (15 minutes), or any time between 0 and 15 minutes.

If you’ve ever been out taking photographs and set a long exposure, and wondered how much time you have left until the exposure will end, this is for you.

For example, if you’ve setup your camera and tripod and figured the correct shutter speed, but need to compensate for increased shutter speed due to Neutral Density filters or other changes, you may have struggled to keep track of the exact time before hitting the shutter release or remote button again. Or you may be standing in the dark, freezing, and wondering what exact exposure time to set, and once it’s set, how much time is remaining.

swipe to set the timer, then hit the green button to run.

This app does the calculation for you, and counts down based on the time you select. Or you can just use the 600 Rule calculator function.

Download on the App Store by going to iTunes and searching forĀ 600 Rule Calculator, or click the links on this page. Hopefully one day I’ll develop a version to run on Android devices.

If you get it, please let me know what you think, and send suggestions for other apps!