The first version was almost the same price with version III originally,
but later I bought the second 1-st version half price. The version III is
today more than twice in the weight and price if I pay the tax. :)

Version 2 has the filter thread and M-mount, but optically same as ver. 1.
Version 3 is much better than ver. 1 & 2 optically, but MFD is a bit longer.