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Baader Maxbright 2" Dielectric Mirror Diagonal

15 April 2003

UPDATE:  It is now more common to find Baader's newer Clicklock diagonal - read my review here.  The Clicklock eyepiece holder used on that diagonal can in fact be used on the Maxbright - ask your dealer for details.

Baader Planetarium has a long history of designing and manufacturing dielectric (enhanced) mirror diagonals.  In addition to their older Maxbright diagonals, they designed and manufactured Astro-Physics' dielectric diagonals until recently.  AP may have terminated their diagonal relationship with Baader a little too soon.  Last year Baader started searching for a way to improve the one weakness of dielectric mirrors - the coating process warps the substrate producing noticeable wave front error.  In fact, other dielectric mirrors often perform worse than 1/4 lambda - the threshold most consider produces visual errors.

Baader's goal was to produce a dielectric mirror with a wave front error of better than 1/10 lambda.  The result is the new Baader Maxbright 2" diagonal.  UPDATE: Baader is now producing a 1.25" Maxbright diagonal which they call the T-2 Maxbright diagonal.  It uses an oversized body similar to this 2" diagonal and the same high-quality dielectric mirror surface.  The oversized body allows interchangeable barrels - even 2" barrels for use in 2" focusers and to allow use of 2" eyepieces.  But still, the mirror is just a bit larger than a standard 1.25" diagonal and you do not get the same aperture as a 2" diagonal.  That said, it is the premier 1.25" diagonal on the market.

Baader achieved this high level of near-perfection with a patented process involving more than 50 layers of dielectric coatings on both sides of the mirror substrate.  Naturally, the back of the mirror doesn't actually reflect anything, but Baader discovered coating both sides kept the mirror perfectly flat.  And, the dielectric coatings, as in all similar mirrors, offer extremely high reflectivity (98.5% in the case of the Maxbright) and are nearly impervious to scratches.  Additionally, dielectric mirrors do not corrode, even in the most humid, salt-air conditions.  This allows the mirror to be cleaned with no fear of damage while producing the brightest possible images for the life of the owner.

The fit and finish of the diagonal and other accessories I will discuss is superb.  All parts are machined and fully anodized or chromed.  All thumbscrews are oversized (two for each connection) and actuate brass compression rings that provide a superior grip on eyepiece, barlow and adapter barrels while protecting them from the thumbscrews themselves.  The threading in the body of the diagonal, for the barrel and eyepiece holder, is very deep, eliminating the possibility of stripping the threads as commonly occurs on budget diagonals.  The entire assembly is absolutely solid.

Figure 1	Attaching a refractor-style diagonal to the rear of an SCT scope is usually accomplished with a 2" visual back or adapter.  Figure 1 shows the Maxbright mounted on the NexStar 11 GPS using Baader's 2" adapter.  You might notice that this looks a lot like the eyepiece holder sticking up from the top of the diagonal.  In fact they are the same part.  This particular adapter is only designed for 11" and larger SCT scope, providing a true 2" aperture.  You must first remove the stock reducer ring and then screw the adapter ring directly onto the rear cell.  The 2" adapter tube is then inserted into the adapter and 6 small hex screws are tightened after orienting the eyepiece holder straight up.  The hex screws fit into a bevel running around the bottom of the tube providing a solid and secure fit.
An added advantage of the Baader Maxbright is that it can be mounted directly to the rear cell of an SCT as shown in Figure 2.  With the NexStar 8/8i/8SE, this allows clearance even when pointed straight up to the zenith.  This requires that you remove the front barrel as shown in Figure 3.  A large locking ring (Figure 4 - also available from Baader) is used to prevent the diagonal from unscrewing and rotating upside down, potentially dropping an eyepiece in the process.	Figure 2 - click for larger image
Figure 3	Figure 4

Figure 5 shows the Baader 2" to 1.25" adapter.  Note the ring sitting to the side. Normally this is threaded to the top of the adapter, but when it is removed, the exposed threads are T-Mount compatible - Baader calls the T-Mount standard T-2.  This allows the direct connection of a film or CCD camera using a camera-specific T-Ring.  Naturally the 1.25" adapter can be placed in the eyepiece holder of the diagonal or directly in the 2" visual back (adapter) on the rear cell for slightly shorter focal length and wider field of view. Baader also makes a complete line of adapters for mounting film, CCD, digital and video cameras to your scope.  Figure 6 (sorry, the image doesn't really do these parts justice) displays, top to bottom:

Figure 5

A T-2 (T-Mount) adapter ring that threads into the top of the diagonal after removing the 2" eyepiece holder.  This allows convenient location of a camera when using the corresponding T-Ring or adapter ring for your camera. A T-2 extension tube - 15mm high.  Baader produces these in several lengths to achieve the perfect focal distance for your camera.  Remember that 2" to 1.25" adapter?  You could insert an eyepiece into it, then thread one of these extension tubes on top and attach your digital camera (with the correct T-2 adapter for your camera) on the extension tube for excellent afocal results.  For added flexibility, Baader makes an adapter called OPFA that allows variable length positioning behind the eyepiece for a better fit and more flexibility.  Both of these options are much more stable than the more common adapters that require set screws attached to the grove exposed in the top of an eyepiece after the rubber eyecup is removed.  Plus, you are not nearly as limited in eyepiece selection.  Visit Matthias Bopp's web site (www.dd1us.de) for an article on OPFA. A standard T-Ring for Canon SLR cameras - not from Baader, but widely available.

Figure 6

Optically, the diagonal is perfect.  This is comparing the image with the diagonal to the image without the diagonal (eyepiece directly in the visual back).  Considering you want the diagonal to be optically invisible, I don't know a better way to test it.  Mechanically, as I mentioned above it is built like a tank.  And I'll report back in 50 years or so on the durability of the mirror itself :-)

The only potential drawback is price.  The Maxbright is not yet commonly available outside of Europe, but I estimate the price of just the diagonal to be about $400 US (cost will vary with the Euro/US Dollar exchange rate).  If you are interested in owning the last diagonal you will ever need, in North America you should contact Alpine Astronomical (www.alpineastro.com).  Alpine also carries most Baader T-2 system adapters.  In Europe, all products are available directly from Baader Planetarium (www.baader-planetarium.com/en/).

Copyright Michael Swanson     Contact the webmaster: swanson.michael@usa.net