Baader Mirror Diagonal - 2" ClickLock

Part of Baader's Modular System

Many telescopes ship with a simple star diagonal that is fine at first; Baader's diagonals are part of a large, modular system: they make very short adaptations possible, provide threads for direct connection to a telescope or a Baader focuser, and adapt to a wide range of threads for torsion-free use with heavy or long accessories such as binoviewers.

The Dielectric Mirror

The oversized 2" mirror has 1/10 wave surface precision and a dielectric coating; the mirror diagonals in this family have a borosilicate mirror and 140 coating layers for 99% reflectivity. Baader's dielectric coating is optimised for the visual part of the spectrum: like a UV/IR blocking filter, it has its highest reflectivity in the 400-700nm range and does not pass other wavelengths to the eyepiece. It is absolutely scratch-resistant and suited to the everyday life of a public observatory, and the coating technique keeps the flat mirror surface from warping under the stress of the many layers.

The hard-coated mirror surface allows safe cleaning and remains scratch-resistant even in extreme conditions. The dielectric mirror reflects only the visual part of the spectrum (400-700nm), so that no UV or IR radiation reaches the eye, and it provides high security for solar observation in white light and with H-alpha solar filters; however, it does not replace the diagonals of H-alpha telescopes with built-in blocking filters.

The 2" ClickLock Clamp

Baader's 2" ClickLock clamp has no clamping screws: a 20° turn of the rotary lever with light pressure holds 2" accessories securely. Like a quick-action chuck, it holds the inserted item on three sides, and leverage multiplies the torque; a ratchet lets you hear and feel whether it is open or closed, and the massive tension ring holds accessories without scratches. Every eyepiece is aligned parallel to the axis automatically, even with diameter deviations.

The position of the rotary lever is adjustable for left- or right-hand use, by six slotted screws or six Allen screws depending on the model. The heaviest load tested so far was a complete C14 lifted by the eyepiece in a 2" ClickLock diagonal, a test that is not to be imitated.

Telescope Side: 2" Nosepiece, SC Thread and S58 Dovetail

There are three ways to connect the diagonal to the telescope.

1. 2" Safety Kerf Nosepiece: The diagonal goes into a 2" eyepiece holder like any standard star diagonal. Baader's Safety-Kerf groove system gives the focuser's clamp excellent grip, just like a classic safety groove, and in addition the diagonal cannot tilt if the telescope's clamping mechanism is in an unfortunate position; with a simple safety groove the clamping screws may just miss the groove or sit on its edge.
2. Female 2" SCT Thread: By unscrewing the 2" nosepiece, you expose a female 2" Schmidt-Cassegrain (SCT) thread. This attaches the diagonal directly to a Schmidt-Cassegrain and reduces the overall length. The ClickLock usually has to come off first (six small screws) so it does not hit the focusing knob; the separately available 2" Locking Ring (#2458270) fixes the diagonal in any rotational position, which helps azimuthal mounts reach the zenith.
3. S58 Ring Dovetail: The housing also features an S58 ring dovetail, which allows the diagonal to be directly coupled to Baader Diamond Steeltrack focusers. The diagonal takes the place of the focuser's standard 2" eyepiece clamp, which extends the available backfocus for long accessories such as binoviewers.

46.6mm Clear Aperture and 112mm Optical Length

The clear aperture is 46.6mm with the 2" nosepiece. The M68 version of this diagonal (#2956100Z), with an M68 thread instead of the nosepiece, has a 51mm clear aperture and 109mm optical length.

In its standard configuration with the 2" nosepiece and 2" ClickLock clamp attached, the diagonal has an optical length of 112mm. With a 2" eyepiece in the ClickLock, the required backfocus is 112mm.

Eyepiece-Side Configurations

If you need more backfocus or want to attach an accessory so it cannot get lost, you can remove the ClickLock by its six M2.5 screws at the side. This exposes the S58 dovetail and a female SC thread, and the required backfocus falls from 112mm to about 71.5mm.

• Binoviewer Integration: Using the optional Baader 2"/T-2 Adapter (#1508035), you can create a low-profile male T-2 thread on the diagonal's body. Depending on the available backfocus, a binoviewer can then be attached directly, without an additional T-2 diagonal or a glasspath corrector; the Mark V Großfeld binoviewer, for example, attaches this way.
• Direct-Thread Eyepieces: With the optional 2"/2" Inverter Ring (#1508020), you can create a male 2" SC thread. The Hyperion Universal Zoom Mark IV can then be screwed directly onto the diagonal, gaining 47mm of backfocus.
• Filter Integration: The removable 2" nosepiece features an M48 filter thread on both ends. A 2" filter can go on the telescope side as usual, or permanently inside the body, for example as dust protection or to keep a deep-sky filter in the light path. The demands on a filter's optical quality rise the further it sits from the focal point.

Mirror, BBHS or Prism?

Baader also offers BBHS silver-coated mirrors and prisms. BBHS stands for Broad Band Hard Silver: the silver layer is stabilised by a hard dielectric protective coating. It gives 98-99% reflection from slightly above 390nm up to 2000nm, with no drop in reflectivity at different viewing angles and no stray light from the silver coating; the trained eye sees more colours, especially with short focal length APO refractors, and a conspicuous colour intensification on planets at the highest magnification.

There is no general recommendation, but light passing through a prism is refracted, which behind a fast telescope can lead to colour aberrations; for fast telescopes designed for use without a prism a mirror is the better choice, with the limit somewhere around f/6 to f/7. Refraction in a prism also produces less stray light than reflection on a mirror, which is why many planetary observers prefer a prism, and a prism must adapt to the ambient temperature like the rest of the optics.

This product consists of the diagonal assembly only. Eyepiece reducers, adapters, and other accessories are sold separately.