500 Rule Calculator App – Download on the App Store

My second photography app, 500 Rule Calculator, is now available. To download, click this link.

I haven’t yet gotten too far into really complicated photography projects, but one thing I’ve wanted to try is star trail photography and also shooting the Milky Way. To do this, knowing how to calculate exposure times using the 500 Rule is essential, because you either want star trails in your shot, or be able to keep the stars sharp, with 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 500 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.

500 Rule Calculator is the result.


This app is useful for photographers wanting to know what exposure time to set for star photography (or astrophotography) using the 500 Rule formula.

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 500 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.

only 2 inputs needed – focal length & crop factor

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 500 Rule calculator function.


Download on the App Store by going to iTunes and searching for 500 Rule Calculator, or click the links on this page. Hopefully one day I’ll develop a version to run on Android devices.

500 Rule Calculator

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


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s