How to Build a Cheap and Easy Optical Zoom Lens for Your Smartphone
Love taking photos with your smartphone, but don't have a zoom? This tutorial by Unitips will show you how to DIY one with a few simple parts. All you'll need is 1/4" bolts, washers, and wingnuts (two each), some sheet metal, and a pair of binoculars.
The only difficult part about this build is folding the sheet metal into the right shape for the bracket. You can find the template here, and as it says in the video, it's probably a good idea to practice with a piece of paper (or three) before doing it for real so you know how to fold it.
For more photos of the lens, and to see the quality of the pictures it takes, visit the Unitips Project Page.