Astro-Physics customers have appreciated the brass locking ring on Astro-Physics adapters and 2" Barlow and have urged us to develop a diagonal with this feature. The recessed brass ring is under the thumbscrew location. As you tighten the thumbscrew, the brass locking ring clamps onto your eyepiece. This provides a more secure grip for your expensive eyepieces than the head of a single screw can provide. As an added advantage, the brass will not mar the surface of your accessories.
The diagonal is accurately square to the optical axis due to the CNC machined parts and special mounting method of the mirror. The baffles and flat black interior allow maximum light transmission. It is threaded for 48m filters so that you can change eyepieces with ease without changing the filter.
Consider these dimensions to be sure that the barrel of your accessories will not strike the mirror. When using 2" accessories, the depth from the top of the diagonal to the mirror surface is 1.85". When using 1.25" accessories, the depth from the top of the diagonal to the mirror surface is 2.25"; our 1.25" adapter adds another 0.25" height. Remember that if you add filters to your eyepiece barrels, the overall length changes.
The total optical path length is 4.1", comprised of 2.75" from the center of the ocular opening to the mirror and 1.35" from the center of the objective opening to the mirror.