(Mostly you don't need an dioptre; With the use of single focus adapter)BUT, with ability now closer/better close-focus distance to the object from around +/- 1m(also depending on single focus adapter) to oo/INF WITHOUT Diopter as oppose to the 2m/6.56ft of the Iscoramas, as already known they also need rare and quality and pricey diopters for close work/shooting.
eBay