I bought this several days ago to use my DSLR with my Starmaster dob. The OCS allows you to increase in-focus (an imaging bugaboo with many newts). The OCS only adds 1.3 magnification while correcting coma and adding adjustable in-focus. If you are interested in imaging with your big dob, this is the solution.
It works great with binoviewers, too :>)
$225.00 and I'll pay to ship 2nd day FedEx in U.S.