Baader Planetarium 2" BBHS® Mirror – Adjustable Star Diagonal

The dielectric coating has its highest reflectivity in the 400-700nm range, while BBHS® (Broad Band Hard Silver) gives 98-99% reflection from slightly above 390nm to 2000nm. The trained eye sees a greater colour range, especially with short focal length APO refractors, and the silver layer produces no stray light.

There is no general rule, 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. On the other hand, refraction in a prism 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. As a guideline, prisms suit about f/6 to f/7 or slower, and BBHS mirrors suit faster optics.

Yes, the mirror is mounted in an adjustable cell that allows for precise user collimation. Baader sets it at the factory and you will not need to change it in normal use. Please note that adjusting the mirror voids the factory warranty on the collimation itself, but the overall product warranty remains valid.

A 20° turn of the rotary lever clamps the accessory, which is held on three sides like a quick-action chuck and aligned parallel to the optical axis; leverage multiplies the clamping force, so even heavy accessories are held securely without tilting.

The 2" BBHS mirror diagonal with 2" ClickLock clamp, and the 2" nosepiece to 2"/SCT thread with Safety-Kerf (#2408156). Baader ships its 2" diagonals without a 1.25" reducer; the ClickLock 2" to 1.25" reducer (#2956214) is available separately.

Yes. The 2" Safety-Kerf nosepiece (#2408156) has a standard 2" (M48) filter thread on the telescope side and a second M48 female thread inside, so a 2" filter can be mounted 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.

Yes. All Baader 2" star diagonals can be attached directly to the end of a Diamond Steeltrack focuser through the S58 dovetail, in place of the focuser's 2" eyepiece clamp, which extends the available backfocus for long accessories such as binoviewers; the focuser can be rotated to bring the eyepiece into a comfortable viewing position.

Yes. The diagonal has an internal 2"/SCT Thread (50.8mm). Unscrewing the 2-inch nosepiece exposes it, so the diagonal can be screwed directly onto a Schmidt-Cassegrain to reduce the overall length. The ClickLock usually has to be removed first (six small screws) so it does not hit the focusing knob, and the separately available 2" Locking Ring (#2458270) fixes the diagonal in any rotational position.

They allow direct, rigid connections:

• S58: A dovetail for direct connection to Baader Diamond Steeltrack® focusers.
• M55: An inner connection on both the telescope and eyepiece sides, used for example by the M55a/M68i (#2458234) and M55a/M68a (#2956110) adapters.
• M48: The standard 2-inch filter thread, on both ends of the nosepiece, and a telescope-side inner connection.

Baader BBHS mirrors make very short adaptations possible through threads for direct connection to a telescope or a Baader focuser. Screwing the diagonal onto a Schmidt-Cassegrain through the 2"/SCT thread, or attaching it through the S58 dovetail to a Diamond Steeltrack focuser in place of the focuser's eyepiece clamp, removes the separate eyepiece clamp from the light path. For binoviewers, Baader's compact T-2 prism diagonals have a much shorter optical length.

Baader uses glass-ceramic with a low coefficient of expansion as the substrate for its BBHS coating, and credits it with very fast temperature adaptation and image stability. The mirror has 1/10 lambda surface accuracy.

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.