Butterfly in a greenhouse

[NickWonfor]

What tips can you give me on capturing subjects which move around a lot making it more difficult to setup the shot?

This image is part of a set of shots I took in order to try and get the hang of macro photography. I do not have a macro lens but am considering buying one.

Taken on a Canon 350D, F4, Shutter Speed 1/40, 70mm on a Sigma 70 - 300mm using an extension tube and no flash.

Due to the extension tube I lost a fair amount of light. I was using a tripod but because I was in a hot greenhouse the butterflies were very active and I needed a quick shutter speed which meant a larger apperture.

Since taking this I've bought an external flash and been given an extension lead allowing me to hold or fix the flash away from its normal position on top of the camera.

A set of extension tubes costs 1/3 as much as a dedicated macro lens and although I enjoy macro photography I don't get to do it often so I'm not sure if it's worth buying a special lens.