#933 45° 1.25" prism for ETX-60AT/70AT
This 45-degree viewing angle image erecting diagonal has a knurled ring that threads onto the Cassegrain focus at the rear of Meade ETX-60AT and 70AT refractors only. It will not fit the Meade ETX-90/105/125 scopes (use #932 instead on these models) or any other telescope. The #933 has a built-in Barlow lens that is needed to transfer the image through the longer light path of the image erecting prism. This acts to boost the power of any 1.25" eyepiece by 2.4x, so lower power eyepieces are generally recommended. For example, the standard equipment 14x eyepiece supplied with the ETX60 and ETX70 scopes becomes a 34x when used with the #933, while the standard equipment 39x becomes a 94x. Since the rule of thumb for terrestrial observing is that the maximum usable magnification with refractors is about 1x per mm of aperture, it can be seen that the built-in 2.4x magnification could cause problems if too high a power eyepiece is chosen. A chrome thumbscrew holds eyepieces firmly in place. It is fully coated for high light transmission.