Macro example

As promised, the following is an example of what extension tubes do.  I'll leave the more detailed description to the makers of the tubes themselves, Kenko, but essentially the extension tubes allow a camera's lens to focus closer to it's subject.  This has the effect of magnifying the image being taken. 

The extension tube set that I bought has 3 different tubes;  a 12 mm, a 25 mm and a 35mm.  The lens that I've us for this example is a Canon 50 mm, f1.8. 

This first shot (of a pin cushion) uses no extension tubes, just the lens.  I focused as closely as possible on the pin cushion.

 The next shot used only the 12 mm extension tube and was focused as close as possible:

 This one used the 12 mm combined with the 25 mm extension tubes, focused as close as possible:

 On this last shot, I used a combination of the 12 mm, 25 mm and 35 mm extension tubes: