For a while these stick on jewels and bits and bobs have been floating around the house (not literally, that would be scary - they've just been in a little jar on a shelf). Anyhoo, I thought I'd try to take some pictures of them. I bought some extension tubes off eBay some time back and I wanted to see if they work.
You can use extension tubes if you have a camera which uses interchangeable lenses. The tubes fit between the lens and the camera and have the effect of drastically decreasing the focus distance, making it much easier to take pictures of tiny things. The tubes usually come in sets of two or three, which you can combine to get different focus distances.
These are a rather racy red colour, which is nice I suppose, but the important thing is that they preserve all the electrical connections between the camera and the lens, so that focus and aperture control all still work. You can pick sets like this up on eBay for less than twenty pounds or so, and they are fun to play with. Make sure you get the set that matches your type of camera.
When you start to use them you'll discover that you can focus very close to things (beware of bashing the lens into the thing you are taking a picture of) and that the depth of field (the range of parts of the picture that are in focus), is very shallow. You can address this by adjusting the aperture, try using F8 or so, but then you'll need a lot more light.
I take lots and lots of pictures with the camera on continuous shooting, and rock slowly backwards and forwards during shooting so that the focus changes. Then I go back and pick the ones that I like the best .If you use a larger aperture (F4 or so) then you can get some interesting effects where not all the picture is sharp.
The tubes worked fine, and I got one or two shots that I'm happy with.