I already have this Denkmeier OCS ....came with my Denk Bino Set.
These are screwed ' IN TO ' not ' ON TO ' a TeleVue or Astro Physic 2'' Diagonal there by ' shorting ' the focal path when using the Denk Bino II in Refractors .....
completely eliminates any ' vignetting ' ( on certain f/l eyepieces )
with the Denk II Bino's....
Here is a ' clip ' from Russ Lederman showing the OCS in question.
http://www.youtube.com/watch?v=EvXlr...ature=youtu.be
This ' screw in ' OCS does away with the standard ' screw on ' OCS generally supplied with the Denk II Bino's.
Some how I have ended up with 2 of these ' newer ' OCS .... 1 is used on my NA140 . . . the other is in a box housed in its aluminum holder.
BTW the new OCS is called ' SR ' . . . or Part No SR
Flash . . .. .