45° Erecting Prisms: All ETX models include an internal flat mirror to reflect light to the telescope's 90° astronomical observing position; in this position the telescope's image is upright, but reversed. For terrestrial observing the 45° Erecting Prism results in a correctly oriented image and a convenient 45° observing angle. #932: for ETX-90EC, -105EC, -125EC. #933: for ETX-70AT.