This may be of interest. I see Cambridge in Colour has added some articles on macro.
Intro link
http://www.cambridgeincolour.com/tec...aphy-intro.htm
Macro lenses with calculators for Magnification, Magnification and sensor size, Macro dof calculator, Diffraction limit calculator.
http://www.cambridgeincolour.com/tut...cro-lenses.htm
Extension tubes and close up lenses
http://www.cambridgeincolour.com/tut...es-closeup.htm
Don