Adding a 25mm tube to my 50mm Macro lens?

I've got the Sigma 50mm Macro lens for my crop camera, it works well and offers great bang for the buck. I wouldn't mind being able to go beyond 1:1. An acquaintance has a Canon extension tube EF25 II for sale for $75. With the short working length of my 50mm, would I be able to use this tube, or would it result in my having to set the subject on the lens to get it in focus?

Eventually I'd like to go with a 180 Macro lens, but it's not in the finances this year.

Thanks

BroncoAZ,
I have never used the Sigma 50 but you should be able to use a 25mm extension tube with it. However I would recommend a set of Kenko tubes, as it give more options.

A 180 macro isn't going to give you more magnification then you can get with your 50mm but will give more room between your lens and subject (which can really help with lighting also help with live subjects). Getting more magnification (more then 1:1) with a 180mm is more difficult then a smaller macro lens.

The guy sold the tube. I might look into a Kenko set later.

+1 for getting a full set of kenko tubes (36+20+12)

make sure they are automatic so you can use them with lens without aperture ring.

In the very beginning I thought I'd get a Macro lens for Macro shooting, but I also had read that Kenko extension tubes were a much cheaper alternative to the more expensive Macro lenses. So, thats what I've been using up to now and am very very happy with the results I continually get using the Kenko tubes..

I'm attaching one of my many youtube slideshows to show you what the Kenko extension tubes can do.
http://www.youtube.com​/watch?v=gj8Ben7254s