I used a 50mm reverse-mounted on the front of another 50mm. This arrangement allows crystal-clear shots of a 10 mm wide field of view. Unfortunately, it also limits depth of field greatly, not that there is much to start with.... As to the size of this specimen, I use a small (about 6 in.) rule with mm markings. I doubt the extreme accuracy of this rule, but it is quite small, thin, and handy, especially in the field. It must be somewhat accurate here as the size comparison of the subject and full frame size on screen (expressed as a ratio) gives the same result. I don't include size when posting unless I have actually measured, although there are some times I have to approximate it because the animal is constantly moving while I am attempting to measure it. I state such as an estimate. Another clue for me is that anything smaller than 3 mm generally looks pretty bad even after processing it to death. This image came out looking pretty nice despite the extreme cropping involved....