Above, left to right top row: Tele Vue Everbrite, Baader Planetarium ClickLock. Left to right bottom row: Sky-Watcher, Altair Astro Posilock.
At 390g the ‘Sky-Watcher’ 2” dielectric diagonal is the ‘no frills’ plainest and lightest of the four dielectric diagonals featured here. There is a good chance that this dielectric is manufactured by Long Perng. The main body appears to be an unpainted anodised silver coloured metal plate, probably consisting of pressed aluminium. The two plain black metal side plates are each secured to the main housing with three Allen screws. My version of this diagonal was actually bundled with my 80ED DS Pro Evostar. The nosepiece features a slight flare, is well baffled and includes a filter thread. I make about 44~45mm of clear
As these diagonals are often bundled with Synta-made telescopes they don’t have a particularly sparkling reputation and many people seek to upgrade them as soon as possible. Although in my experience there is nothing wrong with the diagonal and it performs admirably. As a decent basic 2” dielectric diagonal it compares well with anything else on the market. My only real concern is with the eyepiece holder itself. The compression ring isn’t particularly problematic but I am always wary of brazed holders. There is always the concern that they have the necessary strength to hold heavy eyepieces securely. Having said that I believe it would take a lot of brute force to physically detach the holder from its housing. I’m pretty sure mine came supplied with a 1.25” adapter. As I rarely used the original adapter I’m not sure of its present whereabouts. Although it was perfectly usable.
The adapter I regularly use with it now was originally supplied with my Altair 60 EDF ED doublet. There are no compatibility issues with the Altair adapter. The Sky-Watcher diagonal is still used a fair bit, although now predominantly with my modified ST80's.
The Altair Astro Premium ‘Posilock’ dielectric is in many respects a very similar design to the Sky-Watcher diagonal. It comes supplied with a 1.25” adapter. The main housing body is most probably cast anodised aluminium equipped with carbon fibre side plates. The aesthetically pleasing black and silver twill weave plates are attached to the main housing with three screws. This appears to be virtually identical to the mounting of the side plates on the Sky-Watcher diagonal body. The three Allen screws used in both diagonals are possibly the same size and thread. The nosepiece also features a similar slight flare, internal baffling, and a filter thread. The baffling appears more matte black than the Sky-Watcher nosepiece which is a tad more gloss.
The Altair nosepiece definitely threads off from its respective housing. The positive lock mechanism is probably responsible for the diagonal’s 525g overall weight (not including the 1.25” adapter). Making it a good 100g heavier than its Baader ClickLock diagonal equivalent. The Altair positive lock mechanism features two pillar holders rather than a collet and is identical to the mechanism shown below in an APM Amici.
In use the positive lock is precise and secure. For extra safety the metal screw at the top of the eyepiece holder can be rotated and tightened/loosened along its own axis as a form of safety lock. I make the clear
In use this is a perfectly decent dielectric and to be honest I can’t tell any real difference with my other 2” dielectrics. Apart from the carbon fibre sides feeling peculiarly sharp to the touch, my only real gripe is its excessive weight. It is only 75g lighter than a 2” APM Amici prism diagonal equipped with the same type of positive lock eyepiece holder. Mirror diagonals are usually a fair bit lighter than their prism equivalents. This weight is quite noticeable on lightweight mounts combined with small
The Baader Planetarium ClickLock #2956100 weighs in at a reasonable 425g. It is supplied without a 1.25” adapter. Baader states that it has 46.6mm of clear
The plate is held in with four screws. The removable nosepiece sports safety kerfs and uniquely both ends of the nose contain M48 filter threads. Furthermore, the rubber gripped click lock eyepiece holder can also be removed from the housing. Like most Baader products this diagonal can be customised somewhat to individual tastes and applications. Unlike the ‘posilock’ type the Baader locking eyepiece holder utilises a brass compression ring. Using a compression ring rather than the ‘pillar’ type of retainers is its only apparent Achilles’ heel. I say this as I once got a 19mm Celestron Luminos eyepiece well and truly stuck in this diagonal. Requiring both eyepiece and diagonal to be partially disassembled to completely extricate them from each other.
The culprit undoubtedly being the undercut on the Luminos barrel that had become enmeshed in the compression ring. The Baader ClickLock diagonal holds every other 2” eyepiece I own perfectly well. Although it has to be stated that most of them don’t have undercuts. This is an aesthetic and ergonomically satisfying diagonal to use and performs very well in every telescope I own that has a 2" focuser. The click lock mechanism itself is smooth and secure in use. Although there is no safety mechanism like the one featured on the ‘posilock’ type. Out of the four featured diagonals this is my personal favourite. It was mainly used in my 60mm Altair EDF. Although recently I've started using it again with my 80ED DS Pro Evostar (that I originally purchased it for).
The Tele Vue DDP-8004 Everbrite diagonal weighs in at 455g (without the adapter). I make the Everbrite to have a clear
It also possibly contributes to its relatively light weight. Without its adapter it is only around 30g heavier than the Baader ClickLock diagonal. Both the adapter and the eyepiece holder itself feature brass compression rings. The rings and the screws for them are high quality and the long thumb screws are very smooth to operate. Neither of the thumb screws are captive. The overall ergonomics of the design are well thought out and the diagonal is a pleasure to use. Unfortunately the nose features a relatively deep undercut. I originally bought the Everbrite for my Altair 60 EDF.
The undercut has given me problems when used in the focuser of the 60mm ED doublet which features a three screw compression ring. Smooth or flared nosepieces don’t get caught on the 60 EDF’s compression ring. Another slight point of concern with the Everbrite was that initially the base plate appeared to be made of a plastic polymer or resin material. This is unlike the 1.25” Everbrite and Enhanced Aluminium models which have metal base plates. Takahashi employ a resin base plate on their 1.25” prism. Although on further inspection the Everbrite proved to have a metal base plate. Not that it would have mattered that much to me if it had been a polymer.
