AF DC-NIKKOR 135mm f/2D

This lens is a mystery.  You can find information online from third parties as to how to use it but you can't find anything from Nikon.  Nikon Imaging does provide a pdf here http://download.nikonimglib.com/archive2/YcrVZ00oXSZ102eGHPE061XWFw47/AFDC135_2D_(27_DL)02.pdf

However it makes no mention of the effect of using the combinations of lens f/stop and defocus image control f/stop.  For that it only provides three pictures with defocus at neutral, R and F.  There are lots of mid-wife tales on how to use it but they are hardly definitive.  And to add to the cacophony of half truths here is some more ...

For the longest time I thought you twist the defocus image control ring to the R numbers to "enhance" blur behind the focused subject, the R(ear) as in rear; and enhance the blur in the foreground if you twist the defocus image control ring towards the F(oreground or front).  If you set your aperture to f/2, then you may set the defocus ring at 2 F or R, so on and so forth.  Of course you can leave the defocus ring at the neutral position rendering no defocus effect.  Notice that, there is an additional click beyond the 5.6 on both sides of F and R, it's not marked but I guess it could be an 8 but who knows.

My question is if I set my f/stop at f/4, must I only set the defocus at 4 either F or R direction or I can set it at 5.6 or even the unmarked 8?  Or I can set it only from 4 or below only, meaning 4, 2.8 or 2 in either directions.  I understand mechanically I can set whatever what I am trying to find out is what is supposed to according to NIKON, the engineers behind the lens.  I think Matt Gringer's videos provide the answer, i.e.  if you shoot at f/2, you should only stay at f/2 R or F.  However if you shoot at f/5.6, you can choose all the defocus points in between the 5.6 F or R, i.e 4, 2.8 or 2.  (Gringer was on a trip in HK and he visited a Nikon center there and some guy explained to him how it's supposed to work he didn't know what he was doing with the defocus ... Granger also repeated this (what the guy told him) on another of his video, I just couldn't find the video now, back then he called himself the Nikon guy).

Again, I never find anything direct from Nikon.

Or never mind.

From shooting with this lens for more than a year, all I could say is given some shooting conditions, it has the most offensively ghastly chromatic aberrations ever, period.

(the effect of the defocus is subtle so I don't bother to test it or use it myself ....  I know it's ridiculous)