Originally posted by othar Close to wide open it won't be that obvious, but the further you stop down the lens, the greater your discrepancies from the intended exposure will be
Someone on another thread who did the "simple" conversion said they did not mind that limitation because they always shot wide open (or nearly). But if you are choosing a lens aperture you must be over-riding the camera's Program mode algorithm and effectively using it in Aperture Priority Auto mode or Manual mode, both of which
M-series lenses already allow, and all that will have been achieved is to enable aperture control from the the thumbwheel on the camera (if a DSLR), as well as (or instead of*) the ring on the lens, and the thumbwheel will not even control the smaller apertures accurately, as others have pointed out.
*Depending on how the conversion is done.