I am currently using Achromat screw in macro filter lenses (Sigma +1.6) on either a Panasonic 100-300 or Panasonic x45-175, and while the IQ is reasonable I would like it to be better. I am photographing Dragonflies and Butterflies and need a good working distance so as not to disturb them, the 100-300 is great for this. Can anybody suggest a true macro lens that I may be able to find second hand, I would think 100mm as a minimum. Also what would I require to mount the lens and also any drawbacks in using a non Panasonic lens.The lens would be mounted on a GH2. Thank you.