I don't know about a 12" dob. I have an 8" dob (Orion SkyQuest) and the Denkmeier Big Easy binoviewers (which is their Standard plus a corrector package) . These binoviewers work fantastic with the 8" dob. I hate going back to one eyed observing any more. The corrector supplied with the Denk's work at 2 different powers with each set of ep's. (1.4x and 2.5x) They work great in my 100mm ED refractor too.
Highly recommended!
Check them out here:
http://denkmeier.com/index.cfm?fusea...TOKEN=13337823