The Takahashi 4-Turret Eyepiece Holder 31.7D is a very convenient tool for quick change of 31.7(1¼”) eyepieces during an observing session to obtain various magnifications. 4 different eyepieces can be attached at one time so that it permits 4 different magnifications by turning the turret.It contains a diagonal prism so it allows eyepiece change in either direction. The turret uses only 81mm of back focus.