Compare: Canon 180mm f/3.5 macro and 70-200 f/4 w/ ex tubes

Steven's last post reminds me of another thing I noticed when I got the Sigma 180 macro: focusing is easier.

When you are working close-up/macros photography DOF is a function of the magnification and aperture (not focal length) and there is not much of it. The gearing on the Sigma lens (and I would assume other dedicated macro lenses) is aimed at giving better control and it is definitely easier to focus, whereas on a lens with extension tubes or closer filter it's very easy to "over-adjust".

Regards,

sounds like the 500d is the best place to start, followed by a macro lens if it works out for me.
thanks
martin

If the goal is to increase magnification using an extension tube, then you ought to be using the tube on a lens with the shortest focal length. Mounting a telephoto zoom lens on a tube is going to result in much lower absolute image magnification then mounting a short focal length lens, like a 50mm.

Check out Bob Atkin's EOS FAQ. He has a nice table listing the effect of the 250D/500D closeup filters and EF 12 and 25 extension tubes on the magnification, working and focus distances of many lenses. You'll see that the magnfication factors are much greater on short focal-length lenses than on telephoto lenses.