I set about writing this utility when I first got my Android phone and wanted to learn to write software for it. There's nothing clever about depth of field calculators - there's a dozen or more for Android already - but this was a useful exercise and the resultant application is arguably more usable than most.

Here's the basic idea from a slightly dated version of the app:

The interface is based on sliders, which addresses the main usability issue I've found with all the other DoF calculators out there. They make you type in the numbers directly, which on a phone keyboard is a total pain. With mine you just move the sliders back and forth until the diagram shows the numbers you want, which makes it much quicker and easier to find the camera settings you need.

Naturally it works properly in landscape too. Actually it's better this way round, especially on small screens.

Note the multiple tabs at the top. Do the authors of all the other DoF calculators not use multiple bodies? Or want to carry multiple lenses? My software allows you to check your options with all your available equipment. (In imperial units too.)

I've tried to keep it flexible - if your camera isn't on my list, but you can find the circle of confusion, you can get the information you need.

Oh, and my software is free, distributed under the GPL licence.

You can find it on Google Code.