Baader Glasspathcorrector 1.25x T2 for MaxBright Binoviewers

Achieving a perfectly sharp binocular image depends on more than the quality of the binoviewer and eyepieces. The prisms themselves introduce chromatic aberrations as light passes through a substantial amount of glass, particularly when used with fast refractors. The Baader Glasspathcorrector 1.25x was developed specifically to compensate for these effects while also helping the telescope reach focus.

Unlike a conventional Barlow lens, its primary purpose is not magnification. Baader explains that the Glasspathcorrector was designed primarily to correct the colour aberrations introduced by the prism system inside a binoviewer.

This correction becomes particularly important with fast optical systems. Prism-induced colour fringing is reduced so that the telescope can retain better image quality and fine-detail reproduction.

Its second important function is optical path compensation. Binoviewers require considerable backfocus, and some telescopes cannot move their focal point far enough outward to reach focus. The Glasspathcorrector shifts the focus outward and reduces the optical length required by the complete system.

The 1.25x version has a 38 mm insertion diameter, while Baader specifies an optical path reduction of at least 30 mm depending on the configuration.

Its 1.25x factor also increases the effective focal length of the telescope. This provides additional magnification with the same pair of eyepieces while simultaneously providing prism correction and optical path compensation.

This version is specifically intended for Baader MaxBright Classic and MaxBright II binoviewers using a T2 connection. It can be installed in compatible T2 star diagonals or 1.25 inch and 2 inch nosepieces to keep the optical path as short as possible.

Baader has also measured the effect of the 1.25x Glasspathcorrector in several configurations. These measurements were performed using a Traveler 105 mm F6 refractor, a pair of 35 mm ED eyepieces, a Großfeld binoviewer and a 90 degree T2 prism.

With the 90 degree T2 prism, measured optical length decreases from 162 mm without a corrector to 144 mm with the 1.25x Glasspathcorrector.

In a straight configuration using a 2 inch nosepiece without a prism, optical length decreases from 112 mm to 94 mm.

With a straight T2 quick changer configuration, it decreases from 123 mm to 105 mm.

When the Glasspathcorrector is positioned in front of the prism rather than between the prism and binoviewer, Baader states that optical length can be reduced by approximately another 15 mm.

These figures relate to Baader's specific measurement configuration and should not be interpreted as universal values for every telescope.

The optical unit of the 1.25x Glasspathcorrector consists of cemented lenses. The lens unit can be removed from its cell and reversed when required by the mechanical configuration.

Correct optical orientation must always be maintained: the convex outward-curved surface must face the telescope.

With a MaxBright or MaxBright II binoviewer using the T2 coupling nut, the Glasspathcorrector is installed in lens configuration B, with the lens cell pointing away from the binoviewer.

To minimise optical length, the lenses are not installed inside the binoviewer itself. They can instead be positioned in a T2 star diagonal or compatible nosepiece, allowing the internal beam splitter to remain as close as possible to the front of the binoviewer housing.

The T2 M42 x 0.75 system also provides extensive adaptation possibilities. The Glasspathcorrector flange can be clamped between compatible male and female T2 threaded components, allowing it to be incorporated into many Baader modular configurations.

This approach can be particularly useful with refractors, Schmidt-Cassegrain and Maksutov telescopes when available backfocus becomes insufficient after adding a binoviewer or another optical accessory.

For Newtonian telescopes, Baader instead recommends the dedicated 2 inch 1.7x Newtonian Glasspathcorrector or an appropriate telecentric system. The 1.25x model described here should therefore not be confused with the dedicated Newtonian version.

The T2 system also enables less conventional adaptations. With camera lenses that provide an accessible T2 thread, a Glasspathcorrector can form part of a system allowing compatible 1.25 inch star diagonals and astronomical eyepieces to be used.

By combining dedicated prism correction, a 1.25x factor and optical path compensation, the Baader Glasspathcorrector provides an important solution for operating a binoviewer on telescopes with limited backfocus or optical systems where prism-induced chromatic aberration becomes significant.

Technical specifications

• Manufacturer: Baader Planetarium
• Product: Glasspathcorrector
• Manufacturer SKU: 2456314
• Factor: 1.25x
• Connection: T2
• T2 thread: M42 x 0.75
• Insertion diameter: 38 mm
• Specified optical path reduction: At least 30 mm depending on configuration
• Primary function: Compensation of prism-induced chromatic aberration
• Secondary function: Outward focal-point shift
• Effective focal-length increase: Yes
• Compatible with: Baader MaxBright
• Compatible with: Baader MaxBright II
• Compatible with T2 prism systems: Yes
• Compatible with suitable 1.25 inch nosepieces: Yes
• Compatible with suitable 2 inch nosepieces: Yes
• Optical group: Cemented lenses
• Reversible optical group: Yes
• Required orientation: Convex side towards telescope
• T2 coupling installation: Lens configuration B
• Refractor use: Yes
• Schmidt-Cassegrain and Maksutov use: Possible depending on adaptation and backfocus
• Recommended for Newtonians: No, Baader provides a dedicated 2 inch 1.7x model
• Conventional Barlow function: No

Baader measured optical-path examples

• 90 degree T2 prism without corrector: 162 mm
• 90 degree T2 prism with 1.25x: 144 mm
• Straight 2 inch nosepiece without corrector: 112 mm
• Straight 2 inch nosepiece with 1.25x: 94 mm
• Straight T2 quick changer without corrector: 123 mm
• Straight T2 quick changer with 1.25x: 105 mm
• Positioned in front of the prism: approximately another 15 mm reduction in Baader's test configuration