Gary it is this one
http://www.buytelescopes.com/product...=&pid=5598&m=5
It screws into the AP 2.7" focuser.
For a Newtonian an MPPC is the way to go.
I think you have to go to specially designed expensive FR's for Newts for wide flat fields.
Any decent doublet will work as a FR with an APO. It is just a matter of working out optimum distances for placement.
To keep the thread relevant. That is great Andrew that you got Comet Lovejoy centered. Did you realize you had a 344mm at F4.3?
The 'new' FR should give about F5 at 400mm focal length.
Bert