2" Dielectric Comparison

[Nightspore]

 

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. I have no idea who the OEM is. It may actually be manufactured by the Suzhou Synta Optical Company. 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. Mine now has a replacement GSO thumb screw in the eyepiece holder. There’s nothing inherently wrong with the original screw, I just prefer the longer Guan Sheng Optical one. Interestingly, both screws have the same size threads. 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 aperture. I’m guessing the nosepiece is threaded into the body but mine is too tight to loosen and I don’t want to force it to discover how it is actually attached. The metal eyepiece holder is almost certainly brazed into the main housing body and features a brass compression ring. The diagonal feels solid and well made. Its dielectric mirror gives a bright image with no defects or aberrations that I can detect. In my experience light scatter is not a real issue and no better or worse than my other dielectrics.

 

 

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.

 

 

 

 

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 aperture to be the same as the Sky-Watcher at about 44~45mm.

 

 

In use this is a perfectly decent dielectric and to be honest I can’t tell any 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 aperture short tube refractors. Oddly, these Altair diagonals usually retail at exactly the same price as the 2” Sky-Watcher dielectric. After sitting in a cupboard for a couple of years my Altair dielectric is now regularly used with my modified ST102 on a Vixen Porta II mount and a Vixen APP-TL130 tripod combination.

 

 

 

 

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 aperture, and I believe them. The housing body is white in appearance and feels comfortable to the hand in a tactile sense. Overall it is very well constructed with a high build quality. The oversized 1/10 wave mirror is held in place with a metal base plate separated from the main housing by what appears to be a red rubber gasket.

 

 

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 mainly gets used in my 60mm Altair EDF. As the diminutive doublet gets out far more than any of my other scopes, the Baader ClickLock gets to see (or reflect) a great deal more of the night sky than the other diagonals.

 

 

 

 

The Tele Vue DDP-8004 Everbrite diagonal weighs in at 455g (without the adapter). I make the Everbrite to have a clear aperture of 46mm. This is the most expensive diagonal reviewed here. It costs about two thirds more than the Altair and Sky-Watcher dielectrics and up to a third more expensive than the Baader ClickLock. However, there is also a slightly less expensive version on the market that utilises a mirror constructed of enhanced aluminium. The build quality is very high, like all Tele Vue products. That, and the fact that it is almost certainly manufactured outside of mainland China, probably accounts for its high retail price. Apparently the dielectric coating is applied to Pyrex with a 1/10 wave flatness. The housing is finished in matte black and well baffled. Unusually it has a body machined from a solid block of aluminium with the mirror being held in place by a base plate. The solid block design is to ensure that the nosepiece or eyepiece holder cannot accidentally be unthreaded in use.

 

 

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 2” Everbrite is that the base plate appears 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. Whether this plastic is employed for reasons of weight or economy is not known. It is slightly disconcerting on a diagonal costing just over three hundred quid though.

 

 

Edited June 29, 2021 by Nightspore

[MarkAR]

Good review. So visually there is very little difference but build quality, weight and clamping mechanisms could sway choice.

 

[Nightspore]

7 hours ago, MarkAR said:

Good review. So visually there is very little difference but build quality, weight and clamping mechanisms could sway choice.

 

 

Thanks. Yes, basically that's my experience. They all have their respective positive and negative aspects with design and build. I can't tell any real differences with the performances of the different dielectric mirrors. Their build qualities may differ somewhat, although the only real difference that I can see is that the Baader has a slightly bigger mirror than the others. The Altair is probably the best value for money, it's built like a tank. The Baader is the most adaptable and versatile. The TV's very nice and beautifully constructed. I'm convinced it wouldn't cost 300 quid if it was made in China. 

[Marmot]

My 2” diagonal is the STELLAMIRA dielectric. (My 1.25 is the Skywatcher).

I have read that the StellaMira is identical to that produced under a different brand name (although it didn’t state which one). However, when it is compared to the Skywatcher deluxe dialectic, it looks identical (in pictures at least as I haven’t seen one close up).

I can’t compare it to anything else as it’s my one and only 2 inch diagonal. What I can say (and this will show my lack of experience with these things) is that when I received it I was quite surprised at the size and weight of a 2” diagonal compared to a 1.25” !

[Nightspore]

1 hour ago, Marmot said:

My 2” diagonal is the STELLAMIRA dielectric. (My 1.25 is the Skywatcher).

I have read that the StellaMira is identical to that produced under a different brand name (although it didn’t state which one). However, when it is compared to the Skywatcher deluxe dialectic, it looks identical (in pictures at least as I haven’t seen one close up).

I can’t compare it to anything else as it’s my one and only 2 inch diagonal. What I can say (and this will show my lack of experience with these things) is that when I received it I was quite surprised at the size and weight of a 2” diagonal compared to a 1.25” !

 

As far as I know a lot of StellaMira accessories are often rebadged GSO and Long Perng products. 

 

 

Like these GSO SuperViews. 

 

 

My guess is this Baader Amici is a variant Long Perng XP-E.

 

 

These Amicis are sold under a variety of brand names. The adapter in the above picture is aftermarket. The housings are quite distinctive and your StellaMira is possibly a variation on the XP-G02 series. 

 

 

I'm pretty convinced this 1.25" 'Omegon' Amici is an XP-H. Long Perng have always manufactured good quality products. 

 

 

The 'Sky-Watcher' focuser on the left is almost certainly Long Perng. The 'TS Optics' on the right is GSO.

[Marmot]

You’re spot on. The housing on the Baader Amici you show is identical to mine. Even the thumbscrew looks the same and the general gloss finish to the surfaces.  It seems a well engineered item to me and certainly one that I am happy to trust to hold my one and only 2” eyepiece. There is something nice and secure about a 2” diagonal, even with a 1.25” eyepiece in it via the adapter. Maybe it’s just psychological, but due to its size and bulk it just feels very business like.🙂

[Nightspore]

26 minutes ago, Marmot said:

You’re spot on. The housing on the Baader Amici you show is identical to mine. Even the thumbscrew looks the same and the general gloss finish to the surfaces.  It seems a well engineered item to me and certainly one that I am happy to trust to hold my one and only 2” eyepiece. There is something nice and secure about a 2” diagonal, even with a 1.25” eyepiece in it via the adapter. Maybe it’s just psychological, but due to its size and bulk it just feels very business like.🙂

 

Long Perng stuff is very distinctive. I doubt I could break the EP holder on my Long Perng/Baader Amici but this 1.25" Omegon/Long Perng did.

 

 

When it happened it didn't completely detach. But it was loose and could be rotated. It actually takes a lot of force to detach it from the housing. 

 

 

I'd been using it for twilight lunar viewing with a Barlow and a zoom. Whether it was a weakness inherent in that particular diagonal or the combined stress of the Barlow/zoom combo (or both), I don't know. 

Edited June 30, 2021 by Nightspore

[MarkAR]

16 hours ago, Nightspore said:

 

Long Perng stuff is very distinctive. I doubt I could break the EP holder on my Long Perng/Baader Amici but this 1.25" Omegon/Long Perng did.

 

 

When it happened it didn't completely detach. But it was loose and could be rotated. It actually takes a lot of force to detach it from the housing. 

 

 

I'd been using it for twilight lunar viewing with a Barlow and a zoom. Whether it was a weakness inherent in that particular diagonal or the combined stress of the Barlow/zoom combo (or both), I don't know. 

Ouch, that's a lot of "angular momentum ???" on that joint.

[Nightspore]

2 hours ago, MarkAR said:

Ouch, that's a lot of "angular momentum ???" on that joint.

 

Yeah, it could have been the leverage factor. Having said that the zoom and the Barlow are fairly lightweight. I had another 'Omegon' Amici and actually tried to thread the holder out of the housing. This was before I realised it was brazed in. It takes a lot of brute force to actually loosen/break the holder. Even then it won't actually detach from the housing without a fight.

 

 

These days if I put a zoom into a Barlow it is always used in a 2" diagonal. 

 

 

Although I do use this small Orion zoom/Baader Barlow combo in a 1.25" TV Everbrite. 

 

 

This Baader sital mirror diagonal in my 60 EDF is pretty solid though.

Edited July 1, 2021 by Nightspore

[Marmot]

This sounds like a good argument for using a 2” diagonal for the added security factor, even if just using heavier 1.25” eyepieces. The only obvious disadvantage I can see is that the added weight could upset the balance of the scope.

[Nightspore]

47 minutes ago, Marmot said:

This sounds like a good argument for using a 2” diagonal for the added security factor, even if just using heavier 1.25” eyepieces. The only obvious disadvantage I can see is that the added weight could upset the balance of the scope.

 

Weight and balance can be an issue for me on the AZ5 mount. Some slightly oversized Baader 1.25" diagonals can even be used with 2" nosepieces and holders.

 

 

I only use 1.25" accessories in them, but they're pretty strong.

 

 

The diagonals with weaknesses are resin bodied with metal nosepieces/eyepiece holders or 1.25" with brazed eyepiece holders.