Zalem

Agree 1000%.

His front ring enables you to attach the HCDNA safely (75mm threads) AND it also locks focus on the Kowa which means you don't have to worry about torque. It's an amazing product for a good price. Very nice guy as well.

I assume the 16-S has the same front diameter as the 16-D. Amazing lens, very underrated.

HTN adapters makes front rings for kowa 16D.
Talk to HuuTuan for an advice.
His rings are best solution than any clamp by far.

Yep, small & no moving parts.
Never seen any distortion with the Isco Widescreen 2000 or it's smaller counterpart the Isco S8/X2 - again, small lenses & no moving parts, as they're fixed focus.
Just got to remember that Anamorphics are completely different from spherical lenses - for the most part, you just aren't going to get this lovely pristine look. Most people who turn to anamorphics tend to like & want all the imperfections, what is normally described as a lens having character. They're not for everyone, that's for sure. If you just like the flares, then there are plenty of options out there - blue streak filters etc. Same goes for Oval Bokeh - you have options now.
IMHO it's sacrilege to want to make these lenses fit into a prescribed look. They have their own look, which a lot of people love & you adjust yourself for the really serious distortions (like the big fat heads in close ups). It's like that Lens thread that has been overtaken by certain people posting examples of newish lenses, which you can find examples of all over the net - it kinda ruins the whole point of why that thread was started in the first place. Love the vintage look, gotta love the imperfections.

"Anamorphic Mumps" occur when you're doing a close up of, say, a person & was a common feature of early  Cinemascope lenses, which was later fixed in some makes, but not all. The Mumps doesn't appear at longer distances. It's basically to do with the fact that at closer range, you loose the x2 squeeze ratio & when you go to desequeeze in post you get the mumps.
What @ken, said is probably correct - the fact that they were also projector lenses would have meant that they would hardly have ever been used to project at close range. Don't know if one Kowa branded adaptor is different from another, but am guessing that they won't be - I was always led to believe that the B&H branded ones just had better QC on the glass used.
So, I'm guessing user error/misunderstanding is to blame for the examples of the mumps that you've seen on the B&H, rather than one example being worse than another. This is common when people start to use anamorphics & is compounded even more by people using wide angle lenses with these attachments to do close ups. So many quirks, not enough time or energy to explain everything.
The mumps is summed up best thus:
"The Problem and the Fix... The problem was called "CinemaScope Mumps", in which the center of the image received less horizontal squeeze when the lenses were focused at short distances. When projected, the center of the image was expanded more than its original compression. In the early days of anamorphic photography close-ups were avoided. When they were deemed necessary, the actor was placed either to the right or left of center where the inconsistent squeeze would pose no problem. It is easy to see what Gottschalk and his team at Panavision were able to accomplish. The upper image is a close up taken with an early Bausch and Lomb CinemaScope lens and the lower image is a 35mm reduction print taken from the newly developed M-G-M/Panavision process. We can thank Panavision that this beautiful woman and all others photographed with anamorphic lenses don't look like broadcaster Cokie Roberts. This promotional photo was produced by M-G-M to promote the new system.

The difference between the two photos is at the same time accurate and deceiving. While the system did yield a CinemaScope compatible print without the distortions of contemporary Bausch & Lomb lenses, in fact the low anamorphic squeeze factor of 1.25x would never have created such distortion had it been applied to the B & L design. By the same token, the prismatic anamorphic design would also never create the distortion even if it was 2:1."
(above quote taken from) http://www.widescreenmuseum.com/widescreen/wingup1.htm
And David Mullen's explanation:
"I don't know the exact mechanics but the squeezed bokeh is actually the byproduct of fixing a problem with early CinemaScope lenses, called the "anamorphic mumps". Basically what happened was that as you focused near minimum, like for a close-up on a 50mm anamorphic (the first focal length made for CinemaScope), the squeeze ratio dropped below 2X. But the unsqueezing is always a consistent 2X by the projector, so the end result was that faces looked slightly fat in CinemaScope.

Panavision solved this with some cams in the lens barrel that compensated as the lens rotated towards minimum focus so that the object in focus is always squeezed consistently by 2X -- but the side effect was that objects out of focus now got squeezed more than 2X and thus look skinny when unsqueezed by 2X during projection.

John Hora explains it in the ASC Manual. It has something to do with the fact that the vertical plane of focus is spherical and thus focuses at a different point than the horizontal plane of focus which comes from the anamorphic elements. Using two astigmatizers and counter rotating the anamorphic elements when focusing, Panavision kept a constant 2X squeeze on the subject but caused out of focus objects to get more than a 2X squeeze. So the squeezed bokeh effect is more obvious as you focus closer and when shooting at wide apertures, which is why the lens breathes as you rack focus."
(above from) http://www.reduser.net/forum/showthread.php?99606-ANAMORPHIC-ARTIFACTS-amp-SQUEEZE-RATIO-QUESTION/page2

Here is a quick comparison between the anamorphic lenses I have.
The goal is to compares the flares and sharpness.
Hypergonar Hi-Fi 2
Dyaliscope Champion
Singer/Sankor 16D (uncoated)
Elmoscope 1
Isco Ultra-Star
Schneider Cinelux.
All shots with :
BMMCC
Mitakon Lens Turbo II
Helios 44-2
Focused to infinity, using a +1 close up diopter (Hama) except for the cinelux which used the Rectilux Hardcore DNA
(Sorry for the misaligned Cinelux shot, didn't see it until edit.)
Shot in Raw 3:1, edited and graded in Resolve. Applied the same color correction to all the shots.
I chose this lens, so that every anamorphic adapter would not show vignetting.
Equivalent focal length is 58 (Helios 44-2) * 0.72 (Lens Turbo) * 2.88 (BMMCC) = 120mm (FF)
The flares from the Hypergonar and Dyaliscope are just epic. 
I really like the subtle flares of the Elmo I
The flares of the ultrastar and cinelux are very muted, as expected.
The Singer (Sankor) 16D shot is just to show what happens if you want to uncoat your lens  
What do you think ?  

Hi, thanks for sharing the information.

However, do you feel comfortable tilting down with the HardcoreDNA simply screwed onto the Kowa 16H/8Z? Is using just the provided screws absolutely secure? I am afraid the Rectilux will unscrew and fall to the ground but maybe I am overreacting. Thought about buying an HTN adapter. Cheers.