Yes I think it was already said, but the problem with the non-electrical tubes is that you have to focus manually and set the aperture manually - this can be tricky on some AF lenses, yet is usually possible.
I haven't spent too much time with it yet have had some great results considering that this is what I paid for it....
http://cgi.ebay.ca/Macro-Extension-T...QQcmdZViewItem
Well, here is my wasp shot to add to the thread...
Full resolution.
Each of these images were taken HANDHELD with no AF. I have a huge working distance aswell with a 300mm lens.
Flower shots are compressed from 10.2 MP to 800x600 px.
This shot is to show that though my 70-300mm f/4-5.6 IS is not an "L" lens it can hold it's own. Handheld at 300mm (no macro tubes).