Taken from a post I made a while back on Flickr. I am posting it here because I recently came across a similar piece on another site and realized that quite a few folks were unaware of this option…
This might be old news for some, but hopefully someone else may benefit from it. This is how I go about getting the extremely close macros and just about all my cameras, digital or film, without spending on expensive lenses. Basically, you take one lens (prime is easiest) and you either mount or hold it backwards to the front of your existing lens (the one on the camera). In other words, you shoot through the lens from the camera lens. What it does is give you the ability to focus on objects as close as about 1/2″ away while zooming in on the subject extremely close with the lens that is on the camera. It sounds complex but it really is simple. There are a few outlets online that sell couplers which will mount 2 lenses end to end called a Macro Coupler Ring (basically a blank lens filter with threads on both sides). This will help you free up the hand you might need to zoom or focus with. Some people also make their own by gluing 2 uv or skylight filters face to face. I simply put the camera on a tripod and hold the inverted lens by hand, which takes a little practice.
If you don’t have a second lens, you can use any old lens really. I picked up an old screw mount 50mm MF lens for 10$ at a flea market and it is more than I need to get the job done. You can also shoot through a loop if you have one. I find the loop tough to use with an SLR but is good for the small lenses on most digital cameras. Either way, it is easy, cheap and can produce some pretty decent effects.