Baader T-2 diagonal prism (Zeiss prism, with male/female T-2
photo thread).
The Zeiss Jena T2 Diagonal Prism offers a large aperture, you have
about 35mm free opening, which is significantly more than with 1.25″. The T2
Housing also enables the connection through suitable 2″ adaptations
at 2″, both eyepiece and telescope side. This application makes
Sense, with devices that have a very tight back focus, where to go with
normal 2″ star diagonal no longer comes into focus.
You can use 2″ eyepieces up to approx. 40mm field stop, despite the
somewhat smaller prisms, the view does not become more restless, only that
outermost edge becomes somewhat darker.