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Astro-Physics Maxbright 2" Diagonal
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This is one of the easiest reviews one could ever do as this is one piece of optical astronomical equipment that, in my view, does everything that might be asked of it as perfectly as possible. I’ve been in the amateur astronomy game for around 25 years and though my means are modest, I do appreciate quality when I see or use it. Having heard nothing but good things about this product and Astro-Physics products in general, when I was upgrading to a 2” diagonal for use primarily with my 9.25” SCT, when the money became available, I bought this diagonal. This was several years ago, before the availability of several other competitive 2” dialectricly coated diagonals, many significantly less costly than this one. Even if I were making the purchase today, though, I’d put this diagonal at the top of my list as the quality would be assured. Besides, it might be the only AP I ever own.
The first impression one gets of this diagonal is of its very high quality. The body is machined from a single piece of aluminum so neither of the tube portions of the diagonal can unscrew—I’ve had this become an issue with another 1 ¼” diagonal from another quality manufacturer, so I appreciate knowing it’ll never come up. The insides of the diagonal are well baffled and very flat black and the portion of the diagonal you’d slip into the focuser or visual back is threaded for 2” filters. The 2” eyepiece holder as well as the 1 ¼” adapter both use, as you would expect, high quality brass compression rings to securely hold eyepieces. The mirror can be easily accessed for cleaning by unscrewing the four screws holding the mirror housing to the back of the diagonal to remove it, exposing the mirror.
The mirror itself is a nicely thick, oversized, piece of unspecified low-expansion glass and the surface is guaranteed to be of 1/20th wave accuracy. The reflectivity is given as 99%, slightly better than the best aluminum coated diagonals, but the appeal of the dialectric coated mirror diagonal is not so much in it’s increased reflectivity, which couldn’t be detected by the human eye, but, rather, the durability and longevity of the dialectric coating, having been developed for use on military optics which might be routinely exposed to blowing dust and sand. As a result, the coatings are likely to prove essentially indestructible under normal astronomical use. I’ve had occasion to gently brush the dust from the mirror surface, but haven’t had to do any cleaning beyond that, but I’m confident that, should I have to, the surface will remain undamaged by a careful cleaning. The dialectric coatings are also said to scatter significantly less light than an aluminum coated diagonal. My own careful observations on planets have shown this to likely be true, with the view definitely a bit “cleaner” with the dialectric diagonal compared to a high quality aluminum coated diagonal.
On a practical level, I much prefer the Maxbright diagonal because it’s so much more solid than the 1 ¼” diagonal, especially with heavier eyepieces, such as a TeleVue Nagler 9mm type 1, and with my Denkmeier binoviewer. I feel much more confident as the scope slews through the sky with a heavy load on this diagonal and it’s not let me down. It’s as perfect a piece of equipment as I’m liable to find and, with reasonable care, should last a lifetime.