sorry but I cannot make the formula work, maybe I'm wrong but after doing the math it would come to 0.5/ 1.5 that comes to 0.33, I do not see how you got to 0.16 meters at the end.
Yes, 0.33m is correct. Which shows how the entire lens focus range shrinks down to a range of only 17cm.
and on another note: why would I use a diopter instead of a macro lens ( which does wfocus to infinity) ?
if it's about a "closer" close focus a macro seems the way forward, not?
To expand on David's points:
Macros are usually better in terms of image quality (unless you use something like Master Diopters), but also more expensive and bulky and may not be part of a lens rental package for the duration of a shoot. By contrast a set of close focus diopters could be easily included in a rental package (or owned by a DP) for both planned and unexpected shots needing closer focus. They can be used singly or stacked, on different focal lengths or a zoom, to get the right magnification or to allow greater distance between lens and subject than a particular macro might.
With anamorphic lenses the minimum focus is not very close and even the rare macros don't get all that close, so diopters are the only real option for very close focus or high magnification shots in anamorphic.
Zooms also don't usually have terribly close minimum focus, and macro zooms don't really exist (in the sense of still having a zoom function at very close distances), whereas diopters allow zooms to focus closer and still act as zooms.
Macros are slower aperture lenses or have limited apertures at very close distances, whereas close focus diopters lose virtually no light and can be used on fast lenses.