I used a 30mm macro lens for these. I find at 30mm, it is way too constricting.
A few common restrictions of short macro:
1.) To obtain 1:1 mag (life-size) with a 30-mm macro lens requires a working distance (WD) of approx. 45-mm (1.75-inches).
2.) Physically difficult to provide adequate light to subject (natural, continuous artificial, or speedlight) at short WD.
3.) Potential of "barrel distortion" at short WD.
Unfortunately, I already found this out. This is why I am saving up for a 100mm macro. I do have some screw on magnifiers that I can play with. They are not extension tubes. By the way, a guy on Craig's list had a very nice set of extension tubes for sale that fit Minolta lenses. They fit Minolta alright-wrong mount! I was in tears. The price was more than right.