Baader T-2 90° Prism Star Diagonal Body with Carl Zeiss Spec Prism and BBHS Coating # T2-01B 2456095

Note: This Baader T-2 90-degree prism diagonal (with Zeiss-spec prism) consists of a diagonal body with prism ONLY and includes no nosepiece or eyepiece holder. It has standard T/T-2 threads at the input face (with female T/T-2 thread on the telescope side) and at the output face (with male T thread on the eyepiece side). This lets you add Baader Planetarium T-2 adapters and accessories to configure the diagonal to your needs.

A Fully Customizable Diagonal Body

One of the key features of this Baader T-2 diagonal – and all Baader diagonals, whether they use prisms or mirrors - is the large free aperture and the flexibility to directly adapt to almost any telescope system, without the restriction of a 1.25" barrel size which may cause vignetting in long focal length 1.25" eyepieces or when using the diagonal with a binoviewer. That is precisely why Baader offers the body of all their T-2 System diagonals without adapters. The clear aperture of this diagonal body is 34mm.

Baader Planetarium has worked hard to make the finest and most precisely-engineered prism-based star diagonals on the market today.This mid-sized and highly flexible Baader T-2 90° Zeiss-spec prism diagonal body is ideal for high-power planetary viewing or for systems where back-focus or space is limited and a full aperture 2" diagonal will not work or is not flexible enough.

The right-angle prism in this diagonal body is produced by the same factory that made these prisms for Zeiss, and it’s the identical prism that Zeiss supplied for use with their exquisite APQ telescopes. The famous Baader Planetarium 7-Layer Multi-Coatings ensure the image is bright and contrast and the oversized prism provides an oversized full clear aperture of 34mm / 1.34".

Highest Contrast and Short Optical Path Length

Like all prism-based star diagonals, it has a short optical path length. It exhibits minimal light scatter and provides high contrast images. Its reflective properties do not degrade with age. The prism is mounted in a precisely machined aluminum housing to ensure the glass remains in the correct location and orientation for maximum performance and long life.

Note: This diagonal body uses a prism made under license for Baader by the same production facility that made this item for Zeiss and to the same exacting Zeiss specifications. This "Zeiss-spec" prism was made for Baader and it is not an actual Zeiss-branded prism.

Most prism diagonals, including the Baader T-2 diagonal with a standard prism (Baader part T2-01C or 2456005), rely on total internal reflection at a 45-degree angle within the prism to direct light to the eyepiece. This approach results in high reflectivity without the need to use a reflective coating. However, when relying on total internal reflection, the reflectivity can degrade if dew or dust gets on the surface of the diagonal hypotenuse. That’s why this T-2 diagonal with the Zeiss-spec prism employs a Baader BBHS (Broad-Band Hard Silver) coating on the hypotenuse. This hard and long-lived silver coating enhances reflectivity, even at angles other than 45 degrees, so the product has enhanced performance and long life.

This 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.

The smaller size of this diagonal is a great advantage with smaller fork-mounted compound telescopes where larger 1.25” and 2” diagonals cannot ‘swing through’ the fork.

Configuration Suggestions

You can configure the T-2 Zeiss-spec prism diagonal to exactly suit your viewing requirements. The input and output T/T-2 threads integrate with the full range of Baader Astro T-2 System components and other T-threaded adapters. The telescope side can be configured to fit 2" or 1.25" focusers, as well as directly onto telescopes with specific threads such as original M44 Zeiss threads, Vixen OTAs, or Russian Maks.

The eyepiece side can be configured with 1.25" eyepiece holders. Or it can be used with Baader's quick change ring #6 to mount the Mark V binoviewer to achieve the shortest possible backfocus distance between telescope and binoviewer. It’s also the perfect diagonal for the Baader / Zeiss Giant Binoviewer (it replaces the normal prism diagonal) as well as the Baader Maxbright Binoviewer. With the right accessories, this diagonal also integrates well into digital imaging applications.

The effective optical path length of the base T-2 Prism Diagonal with Zeiss Prism is 38.5mm. The diagonal weighs just 5.4 oz (153g).

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

Manufacturer part number: T2-01B or 2456095.