So you always wanted to be a scientist...except you aren't. Never fear! The iMicroscope iPhone app is here. When used with a microscope (surely you've got one of those kicking around?) you can take ultra-precise scientific photos.
Whatever you put on the microscope slide—my hot tip is a slice of watermelon, or a strand of hair—you'll be able to see just fine through the viewfinder of the device. But what if you want a photo of it in all its magnified glory? You download iMicroscope (for $2.99) and take a photo down the eye of the viewfinder, with the app then requiring you to insert the level of magnification you were looking at, for example 40x.
After that, the image is displayed, letting you zoom in and out, with a scale bar down the bottom for reference. You can email the image, or save it to your camera roll—and when you go back to it later, it will auto-format to the magnification you last viewed it in.