I was skeptical of this iPhone camera tip posted by Alex Wild at Scientific American, and had to try it for myself. Wild claims that using just a drop of water, you can turn the iPhone into a capable microscope, letting you take photos of objects right up to the lens. Obvious concerns about intentionally putting water on an electronics device are warranted, but this trick looked fairly safe, given that the iPhone's water sensors aren't located near the camera lens. Still, water can be unpredictable, so I used an eyedropper and kept a paper towel at arm's reach during the test.
The upshot: it works! My process is documented below, along with photos, if you're interested. Applying a drop of water was extremely simple, and I just had to flip the phone over quickly to avoid the water sliding off the lens ring. Like Wild, I found that a larger drop of water yielded better results--not just higher magnification, but better centering as well--and photos were best when both the iPhone and subject were held still on stable platforms. One commenter noted that using glycerine instead of water also works, since the substance is more viscous and therefore easier to control. But you can't get that from the sink!
For the initial setup, I placed the iPhone on two empty glasses about 5 inches tall. I also adjusted the iPhone to not automatically turn off its screen and go to standby mode after 30 seconds.
From a typical macro distance of about five inches, objects directly under the camera lens are very clear and focused, as expected.
Apple made a big deal about the macro photo abilities of the iPhone 4S, and the camera's 4.28 focal length and f/2.4 max aperture allows it to shoot better photos than most cameraphones (some Nokia models aside). But move an object closer than four inches to the phone and you'll get a blurry subject, no matter how often you tap the screen to adjust focus. That's just a limitation of the camera.
With a drop of water on the lens, you actually have to place your subjects much closer to the lens than you thought possible. Everything further than 1 cm away from the lens will be a blur; I had to hold this button almost up to the drooping water drop to get this shot. But the result was this really cool photo in which you can even see the CMYK dots that make up the colors on this button!
If you try this yourself, please post some photos in the comments below.