The TUAW staff loves Photojojo, the company that has a website dedicated to selling fun little accessories that are aimed at iPhoneographers. The latest item the staff sent for us to test is the Polarizing Clip On Filter (US$20.00), which is exactly what the name implies -- a little polarizing filter that clips onto your iPhone.
If you're not familiar with what polarizing filters can do for photography, you're in for a treat. Sunlight is polarized in one direction, and a polarizing filter rotates to allow you to block out reflected light off of the sea, beaches and the air. For a complete description of how a polarizing filter can improve your photos, our friends at Wikipedia have a detailed article that describes how they work.
Should you decide not to read the article, let's just say that the sky usually becomes much more deep blue, the surface of the sea or any water loses reflections, and any haze in the air seems to disappear. Here's an example:
For the most part, this little clip on filter works as advertised. However, on my iPhone 5 I always had some part of my photo obscured by the filter no matter how much I moved it around.
That's not going to be an issue as long as you're aware of the vignetting and you're planning on doing some photo cropping after the fact. I was unable to test the Photojojo Polarizing Clip On Filter on any other Apple device, so I don't know if all iPhones / iPad might run into this issue. I spent quite a bit of time adjusting the filter on my iPhone 5 and could never get the vignetting to disappear.
That being said, it does exactly what you'd expect a polarizing filter to do. As you can see from the images below (cropped to remove the vignetting), it can take an overly bright and glaring sunlit image and turn it into a beautiful image with deep blue skies and a gorgeous ocean.
For photographers who take a lot of images at the beach or in situations where there's a lot of reflected light (i.e., on ski slopes), the $20 expenditure for the Photojojo Polarizing Clip On Filter should be a no-brainer. Just be aware of the limitations of the filter and that you might need to edit your images to remove vignetting, and you'll have an inexpensive way to improve your iPhone or iPad photos.