The OCS A45 was designed due to demand! FAST DOBS have very steeply converging light cones coming off the secondary mirror. Since the OCS Optics must go deeply into the converging cone to allow the Binotron 27 to rech focus, we made an optic that simply cannot be any larger in clear aperture and still be held securly in an anodized aluminum cell. The pictures speack for themselves. Used with the Bibnotron-27 Super System this optic grabs thoise outer peripheral rays missed by the OCS A37 and produces a brighter image. Alone this optic costs $249.00. Add it to a new Binotron 27 order and recieve a $100.00 discount! Please see "OCS A45 For New Binotron" under "products" and order it there IF you are also ordering any Binotron 27. A new Binotron 27 order must be placed to recieve the $149.00 price.