Originally posted by Marc Sabatella First, I'd recommend goign to a library or bookstore and getting a good basic guide to photography; these typically cover questions like this, as well as the inevitable questions that you'll have next after getting to the answers to these :-)
But FWIW:
- A longer focal length allows you to shoot from farther away for the same magnification. In this sense, macro photography is no different than non-macro photography. Take your kit lens, set it to 18mm, fill the frame with an object, then zoom to 55mm, and you'll have to step back to fill the frame the same way.
- Since insects typically don't respnd well to having lenses stuck right in their faces, that means longer is usually better. I wouldn't be messing with anything shorter than 100mm, personally.
- Bellows are like adjustable extension tubes, yes.
- Large apertures (eg, f-numbers less than f/2.8) are useful for shooting in low light, because they allow faster shutter speeds, but the tradeoff is very shallow DOF. With macro photography, DOF is already incredibly shallow; far to shallow to be useful a f/2.8, normally. So even if your lens had f/2 or f/1.4, you wouldn't want to use it - you'll normally stop down to f/8, f/11, or even f/16 or more. This often means you'll you'll need flash to provide enough light, but the alternative is a picture with just a tiny bit in focus. Sometimes that's a ncie effect, but it gets old quickly.
- Google "Raynox 150" (including disucssions here) and consider whether that might not be a good way to get started without spending much money.
..or Raynox DCR-250 for that matter.