iPhone 3GS + Hoya R72 filter = near infrared camera

The visible spectrum is light with wavelengths between 400-700nm. An R72 filter blocks all light with wavelengths less then 720nm. Most images sensors in digital cameras are sensitive to light past 700nm in order to make a digital image look like what you see with your eye camera manufactures place a little piece of glass in the camera that blocks this light. Cheaper camera, however, do not and fortunately for us cell phone cameras usually fall under the cheap mark. So, by placing an R72 filter over an iPhone camera we are able to see only light above 720nm that the camera is picking up. Vegetation reflects very well at these wavelengths while the sky and pavement do not giving cool effects such as a black sky or snow white trees. And the best part is you only need the smallest filter to cover the iPhone lens! I bought mine for around $30