This beautiful optical cell is used (And Required) to allow a Binotron -27 with Power Switch to be used on Lunt H-a scopes. This optic is threaded into the telescpe side of the blocking filter diagonal after the hollow tube of the Lunt BF Diagonal on the telescope-side is removed. This optic has female 42mm T threads and the Lunt BF Diagonal has 42mm male threads once the Lunt Diagonal 2" Tube is removed. Also included is a 1.25" nose for the Binotron which threads into the Binotron Power Switch AFTER the Binotron's 2" Nosepiece is removed from the Power Switch. Resulting Power Switch magnifiction factors are 1.3X/2.3X and 3X. Note" The higher power of 3X is difficult to use and out travel of the focuser of the Lunt will likely not allow focus. However, an extension piece that is threaded onto the Optical Adapter on the telescope-side of the optical adapter will allow the entire diagonal to be slided outward and the highest 3X will reach focus. The hollow extension is $39 additional. Just make a note on the order if you want the extra extension. Note that the 1.3X/2.3X magnfications are most recommended because of the thermal currents that occur coming up from the ground due the Sun's heat, especially near noon time.