Also (and this maybe a stupid question, but like I said I have never used extension tubes) can you only use manual focus if you are using extension tubes?
There are extension tubes that allow auto focus, it keeps the electrical connections between camera and lens, and start at $ 70, and work both autofocus and image stabilizer lens. There are also inexpensive extension tubes that do not allow the electrical connection between camera and lens. Beware of them, for some lens models, specifically Canon 40mm need electricity to even do manual focus. Therefore, it is mandatory for Canon 40mm extension tube with electrical contacts, even for manual focus.