Test product for Brian

Star diagonals that use glass prisms as the main reflective component have many advantages over mirror-based diagonals. They have shorter optical path lengths. They exhibit minimal light scatter and provide high contrast images. And, when well made, their reflective properties do not degrade with age.

While many cut-rate optics vendors make poor-quality prism diagonals, Baader Planetarium has worked hard to make the finest and most precisely-engineered prism-based star diagonals on the market today. This Baader T-2 90° Prism Diagonal includes the Baader T-2 90-degree diagonal body with 32mm clear aperture, which itself is available as a stand-alone component [LINK], and it includes a 1.25” nosepiece (T2-14) and 1.25” eyepiece holder (EYEHOLD-2) from Baader’s T-2 system of accessories.

The optics-grade glass prism in this Baader diagonal is precisely ground to the correct angles for maximum reflectivity and polished to minimize loss and scatter at the air-glass interface. The prism is multi-coated to ensure >96% reflectivity, then mounted in a precisely machined aluminum housing to ensure the glass remains in the correct location and orientation for maximum performance and long life.

This Baader diagonal works well for observing nearly all celestial objects. But since it minimizes scattered light and wavefront error, it’s especially good for high-contrast and high-magnification planetary and double-star observation with Schmidt-Cassegrain and Maksutov-Cassegrain telescopes and with refracting telescopes of focal ratio longer than f/7. While this 1.25” diagonal works with telescopes of shorter focal ratio, especially when observing fainter objects, the steeper angles at which light passes through the prism may cause some chromatic aberration when observing planets and other bright objects in faster refractors.

The smaller size of this 1.25” diagonal is a great advantage with smaller fork-mounted compound telescopes where larger 1.25” and 2” diagonals cannot ‘swing through’ the fork. Its shorter path length is also a big advantage where shorter back focus is required such as when observing with Baader’s MaxBright binoviewers.

And since the 1.25” T-2 nosepiece and eyepiece holder of this diagonal are removable, you can swap them out for other components in the Baader T-2 suite of accessories to adapt the diagonal to other telescopes and applications.

NOTE: Like mirror-based star diagonals, but unlike diagonals with an Amici prism, this diagonal gives images that are upright but left-right reversed.