The shorter 2″ sleeve will be a good solution when your scope is a bit scarce of the back-focus.
Innovation of Astronomical Telescope
正立ミラーシステム(EMS)を開発した松本龍郎のサイト。 たった2回の反射で天体望遠鏡の像を正立像にします。
Tatsuro Matsumoto; Inventor of the EMS, Erecting Mirror System. EMS offers non reversed upright image with no additional undesirable abberations.
The shorter 2″ sleeve will be a good solution when your scope is a bit scarce of the back-focus.