Initially, I had high hopes for this new collar, but I'm now convinced it doesn't solve the problem in most cases. My advice is to return the lens forthwith for a money refund, if you are dissatisfied with the tripod collar, or return it for replacement of the tripod collar as a warranty issue. Its performance wide open isn't equally impressive, though. It copes well with extension rings and the setup with PN-11 is very effective in giving a comfortably long working distance eminently suited for shooting shy objects. This was a beautifully built telephoto released in the 60's, but the image quality would not raise eyebrows today.
Images are crisp and sharp even wide open.
Like other superfast long lenses, it should not be stopped down too far. When stopped further down sharpness is rapidly lost. This strange performance pattern occurred identically for two different samples so presumably is typical for this design. The built-in sunshade is way too short and thus the lens flares quite easily under adverse light conditions. Being a light-weight long lens, it is very prone to camera shake and vibration and really needs to be mounted on a sturdy tripod.