Testing small external lenses for phones and other mobile devices
China can make quite interesting gadgets like for example external lenses for phones and other devices. They alter how the built-in lens works allowing for wide field, macro or telephoto effect. Some will even give you fish-eye ultra wide field effect. Such lenses cost few Euros and are quite basic in design. I'll take a look at two of them - 2x telephoto and macro/wide field lens.
You can find such lenses on China-stores like dx.com as well as on ebay and some local stores if you have luck. Note that there are more professional lenses as well, but those much more and aren't covered by this article.
Cheap lenses use a clip mount or a magnet which is more universal. Those I've got use magnets. To use it you will get also sticky metal rings that can be sicked around phone lens. Ring then holds the external lens which has a magnet inside. The 2x telephoto lens will increase the focal length two times - optical zoom. The two-in-one wide field/macro lens by default will give you a wider field of view by reducing the focal length. When you unscrew the top part of the lens you will get macro mode - it will focus only on very short distances.
Those lenses have a basic two element design. This means that there will be field curvature and some chromatic aberration. Lenses should work with most mobile devices unless they have bigger sensors and bigger lenses than average. In such cases you will get vignetting and noticeable image distortion on edges of the frame. It's important to position the external lens straight above the device lens so that you get optimal performance out of it.
I've uploaded all images on flick.com. Below are some cut outs for every device. I've used Toshiba Camileo Clip "sport" camera, Galaxy Young phone and 4th generation iPod Touch.
Camileo is an "outdoor" camera with wide field lens of its own. With external lenses it shows noticeable image distortion due to field curvature as well as some vignetting. Telephoto lens doesn't focus properly. Samsung Galaxy and iPod reach focus and the image quality is quite good. But look on the full frames on flick. Notice how the building on the right is bent when a lens is used. That's due to field curvature.
Macro lens focus at a very short distance and you manage to get it right the image will be sharp, but usually only in the center.
For a cheap and basic lens you can't expect much. For phone cameras they can work, but don't expect it to be a DSLR in terms of quality. They are small so at some occasions they may come in handy. Fun thing.