2" Dielectric Comparison

[Zeta Reticulan]

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 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'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 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 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 aperture short tube refractors. Oddly, these Altair diagonals often 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 was mainly used in my 60mm Altair EDF. Although recently I've started using it again with my 80ED DS Pro Evostar (which I originally bought it for).

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 around three hundred and fifty quid though.

[NGC 1502]

Thanks for your excellent well written review👍

Are you certain the TV diagonal has a non-metal base plate?   Plastics can be excellent and long lasting but I agree it’s disconcerting in such a high end product.

I own 2 TV diagonals.  One is a late model 1.25” Everbrite purchased used for my elderly Vixen 80 achromat that has a 1.25” focuser.  The second is a 2” from the 1990s before Everbrites were made, it’s used with my TV Pronto. The aluminium coating looks fine from the coated side. However when removed for cleaning it does show the first signs of deterioration.  When viewed from the reverse side against a bright light there’s one or two patches that are mildly blotchy.  So for very long term service the Everbrite is a good idea. I also have an unbranded 2” diagonal that came with a used TV85 bought 8 years ago.  Sadly the TV85 suffered abuse in transit. The lens cell had shifted relative to the tube and was obviously out of collimation in use. (TV lens cells are fixed to the tube by 3 screws, not threaded on).

In your section about the Altair diagonal you mention you “can’t tell any real difference” with the others.  I’m guessing you mean the views were similar through all, and that’s my experience with my own diagonals.

Enjoyed your review, thank’s again, Ed.

Edited August 19, 2022 by NGC 1502
Extra info

[Zeta Reticulan]

7 hours ago, NGC 1502 said:

Thanks for your excellent well written review👍

Are you certain the TV diagonal has a non-metal base plate?   Plastics can be excellent and long lasting but I agree it’s disconcerting in such a high end product.

I own 2 TV diagonals.  One is a late model 1.25” Everbrite purchased used for my elderly Vixen 80 achromat that has a 1.25” focuser.  The second is a 2” from the 1990s before Everbrites were made, it’s used with my TV Pronto. The aluminium coating looks fine from the coated side. However when removed for cleaning it does show the first signs of deterioration.  When viewed from the reverse side against a bright light there’s one or two patches that are mildly blotchy.  So for very long term service the Everbrite is a good idea. I also have an unbranded 2” diagonal that came with a used TV85 bought 8 years ago.  Sadly the TV85 suffered abuse in transit. The lens cell had shifted relative to the tube and was obviously out of collimation in use. (TV lens cells are fixed to the tube by 3 screws, not threaded on).

In your section about the Altair diagonal you mention you “can’t tell any real difference” with the others.  I’m guessing you mean the views were similar through all, and that’s my experience with my own diagonals.

Enjoyed your review, thank’s again, Ed.

You're welcome, and thanks. The 2" TV definitely appears to have a non-metal base plate. Unless it's just some form of plastic veneer. It could be that it just seems like it is plastic. I have a couple of the 1.25" enhanced aluminium TV's. They're only a few years old though. Apparently they are better for planetary as they have less scatter than a dielectric. TBH I'm not that sold on dielectrics as a whole. I think Bill Paolini once described them as "a question to an answer". Mind you, that was also said about the laser lol. Yes, basically the views are similar through all of them. The differences are ergonomic and in design in the main. 

Edited August 19, 2022 by Zeta Reticulan

[DavidGinMD]

Looking at my 1 year old 2” TV Everbrite diagonal right now, and the base plate is definitely metal, not plastic or resin. That’s consistent with this post from one of the TV tech support folks: https://www.cloudynights.com/topic/837347-tv-everbright-diagonal-plastic-mirror-mounting-plate/?p=12093843

[Zeta Reticulan]

1 hour ago, DavidGinMD said:

Looking at my 1 year old 2” TV Everbrite diagonal right now, and the base plate is definitely metal, not plastic or resin. That’s consistent with this post from one of the TV tech support folks: https://www.cloudynights.com/topic/837347-tv-everbright-diagonal-plastic-mirror-mounting-plate/?p=12093843

Oh right, thanks. That's a relief. Oh, hold on, I just realised who the author is of that post on CN. Leopards just can't change their spots, can they? 

It certainly puzzled me that the bottom appeared to be a polymer of some sort. I assumed it was a veneer. If it isn't, I'm glad.

Edited August 20, 2022 by Zeta Reticulan

[Zeta Reticulan]

I'd like to straighten Issacs out!

Edited August 20, 2022 by Zeta Reticulan

[Zeta Reticulan]

Addendum:

The plastic appearing base plate is most likely not plastic. Which is quite a relief to be honest. It's worth pointing out that I never stated definitively that it was plastic. I stated that it appeared plastic. 

"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. " op cit 

2. LINK VERB [no cont]

If someone or something appears to have a particular quality or characteristic, they give the impression of having that quality or characteristic.

Collins Dictionary

A leopard just can't change its spots, eh John?

Edited August 20, 2022 by Zeta Reticulan

[F15Rules]

Thanks for a very well written and informative review of some very popular diagonals..

Your conclusions are interesting but not surprising, as many of us have felt, like you, that there isn't a visible world of difference in the optical performance of many diagonals, to most of us, in good UK conditions: under the dry, clear desert skies of Arizona it might be different.

However, there are significant other differences which often inform our buying decisions for diagonals. For example, (and just for my own observing preferences), I list a few points which have in the past, and do now, influence the diagonals I will use (in no particular order):

1. Nosepiece. I really dislike nosepieces that unscrew from the body of the diagonal too readily. I use some heavy eyepieces (one of them, the 2"  Celestron Axiom LX 31mm wonderful eyepiece optically) weighs 1.4kg (😱), and the only diagonals I would trust to safely hold an eyepiece like this are the 2" TV Everbrite and the Baader Prism Diagonals with 2"Clicklock T2 eyepiece holders. I've owned the Everbrite and liked it, but these days I binoview quite a lot too, so have been moving over to the Baader T2 system. I now have a T2 prism diagonal and a T2 Zeiss BBHS prism (both Baader) and am very happy with them.and their security.

2. Undercuts on the nosepiece. As you mentioned, Tele Vue use undercuts on all their eyepieces and diagonals. I loath and despise undercuts! That's the only fault I could find with the Everbrites. 

The Baader safety kerfs such as those on my Morpheus 9mm and 17.5mm are just fine, although I personally prefer the old classic vintage Japanese smooth chromed brass barrels such as used to be on the Circle T and Baader Genuine Ortho units.

3. I like my diagonals to be black, including the threads inside their barrels and eyepiece holders..better contrast, less scatter👍.

4. Eyepiece holders, especially 2" to 1.25", should have as low a profile as possible, (for binoviewing) and two, not one securing screws.

Many only have one, and often too small, so.again I prefer clicklocks, which are pretty much fool-and-bomb-proof.

Given that most things in life are a compromise, I choose Baader as they most nearly tick all my preference boxes.

One last point. I really respect Tele Vue and their products and innovation. However: they have for years refused to lose their barrel undercuts, which is their absolute right. But at their top of the tree prices, I will choose products from a company like Baader who seem to listen to customer feedback and preferences: given that most visual observers I know hate undercuts and prefer smooth barrelled eyepieces, and diagonals, it seems to me a shame that fine products from a company like Tele Vue would be avoided just because of their insistence on retaining such an unnecessary and sometimes damaging product feature?

If they were to switch to smooth barrels, I wonder how many TV afficionados would be genuinely upset versus the number of potential new customers who would be delighted?

Just my "twopennorth worth"😊

Dave

 

[Zeta Reticulan]

4 minutes ago, F15Rules said:

Thanks for a very well written and informative review of some very popular diagonals..

Your conclusions are interesting but not surprising, as many of us have felt, like you, that there isn't a visible world of difference in the optical performance of many diagonals, to most of us, in good UK conditions: under the dry, clear desert skies of Arizona it might be different.

However, there are significant other differences which often inform our buying decisions for diagonals. For example, (and just for my own observing preferences), I list a few points which have in the past, and do now, influence the diagonals I will use (in no particular order):

1. Nosepiece. I really dislike nosepieces that unscrew from the body of the diagonal too readily. I use some heavy eyepieces (one of them, the 2"  Celestron Axiom LX 31mm wonderful eyepiece optically) weighs 1.4kg (😱), and the only diagonals I would trust to safely hold an eyepiece like this are the 2" TV Everbrite and the Baader Prism Diagonals with 2"Clicklock T2 eyepiece holders. I've owned the Everbrite and liked it, but these days I binoview quite a lot too, so have been moving over to the Baader T2 system. I now have a T2 prism diagonal and a T2 Zeiss BBHS prism (both Baader) and am very happy with them.and their security.

2. Undercuts on the nosepiece. As you mentioned, Tele Vue use undercuts on all their eyepieces and diagonals. I loath and despise undercuts! That's the only fault I could find with the Everbrites. 

The Baader safety kerfs such as those on my Morpheus 9mm and 17.5mm are just fine, although I personally prefer the old classic vintage Japanese smooth chromed brass barrels such as used to be on the Circle T and Baader Genuine Ortho units.

3. I like my diagonals to be black, including the threads inside their barrels and eyepiece holders..better contrast, less scatter👍.

4. Eyepiece holders, especially 2" to 1.25", should have as low a profile as possible, (for binoviewing) and two, not one securing screws.

Many only have one, and often too small, so.again I prefer clicklocks, which are pretty much fool-and-bomb-proof.

Given that most things in life are a compromise, I choose Baader as they most nearly tick all my preference boxes.

One last point. I really respect Tele Vue and their products and innovation. However: they have for years refused to lose their barrel undercuts, which is their absolute right. But at their top of the tree prices, I will choose products from a company like Baader who seem to listen to customer feedback and preferences: given that most visual observers I know hate undercuts and prefer smooth barrelled eyepieces, and diagonals, it seems to me a shame that fine products from a company like Tele Vue would be avoided just because of their insistence on retaining such an unnecessary and sometimes damaging product feature?

If they were to switch to smooth barrels, I wonder how many TV afficionados would be genuinely upset versus the number of potential new customers who would be delighted?

Just my "twopennorth worth"😊

Dave

 

Thank you, and you're welcome. At least most TV undercuts now have a lower lip flare. I've heard that TV are reluctant to cease adding the undercuts as it would alter the secondhand value of those with undercuts. I don't know how true it is. 

[F15Rules]

19 minutes ago, Zeta Reticulan said:

Thank you, and you're welcome. At least most TV undercuts now have a lower lip flare. I've heard that TV are reluctant to cease adding the undercuts as it would alter the secondhand value of those with undercuts. I don't know how true it is. 

Yes, I've heard that too, but frankly it doesn't make sense..the products that have already been sold by Tele Vue have already made their margin for the company: put bluntly, they are yesterday's news.

However, if they switched to smooth barrels, and so sold more of their eyepieces, they would make more profit and so protect the future of their brand.

There would always be a market for their older eyepieces, with or without undercuts, as they are such good products - but if they sold more new product following a switch to smooth barrels, well, I rest my case!

Perhaps some good old proper market research commissioned by Tele Vue could give them a data-led steer on what their customers would prefer - say some surveys at astro fairs around the world conducted by their dealers? Minimal cost to do, but potentially major business benefits.

In my experience of working in sales and business/brand development for many years, any company that doesn't canvas market and customer opinion and preferences won't have a business in the long term..

Dave

[Zeta Reticulan]

1 minute ago, F15Rules said:

Yes, I've heard that too, but frankly it doesn't make sense..the products that have already been sold by Tele Vue have already made their margin for the company: put bluntly, they are yesterday's news.

However, if they switched to smooth barrels, and so sold more of their eyepieces, they would make more profit and so protect the future of their brand.

There would always be a market for their older eyepieces, with or without undercuts, as they are such good products - but if they sold more new product following a switch to smooth barrels, well, I rest my case!

Perhaps some good old proper market research commissioned by Tele Vue could give them a data-led steer on what their customers would prefer - say some surveys at astro fairs around the world conducted by their dealers? Minimal cost to do, but potentially major business benefits.

In my experience of working in sales and business/brand development for many years, any company that doesn't canvas market and customer opinion and preferences won't have a business in the long term..

Dave

Yeah, I agree with you. GSO are phasing out their undercuts. I have no idea why TV aren't following suit. 

[Mr Spock]

As for my comparison of the Revelation Quartz 2" and Baader 2" - no difference in image quality detected. However, the Baader Clicklock is addictive 

[Zeta Reticulan]

11 minutes ago, Mr Spock said:

As for my comparison of the Revelation Quartz 2" and Baader 2" - no difference in image quality detected. However, the Baader Clicklock is addictive 

It certainly is an addictive clicklock lol.

[NGC 1502]

1 hour ago, Zeta Reticulan said:

I'd like to straighten Issacs out!

Absolutely no worries at all.  I often get it wrong myself, therefore when someone else does, it’s a big relief😊

[Zeta Reticulan]

2 minutes ago, NGC 1502 said:

Absolutely no worries at all.  I often get it wrong myself, therefore when someone else does, it’s a big relief😊

I'd not had the 2" TV long and I wasn't sure if the base was plastic or not. I thought that if it was it would most likely be expensive plastic. What's most curious about the response from CN is the petty vindictiveness of it all. A virtual lynch mob assembled braying for my execution. It's not like I gave the diagonal a poor evaluation or anything. It's still a very nice diagonal. Even if it had a polymer base. After all Takahashi use them. Still, on CN, it brought out a bunch of little girls who think someone's pulled their pigtails. Honestly, you couldn't make this stuff up. Feel the hate lol.

 

[DavidGinMD]

5 hours ago, Zeta Reticulan said:

Oh right, thanks. That's a relief. Oh, hold on, I just realised who the author is of that post on CN. Leopards just can't change their spots, can they? 

It certainly puzzled me that the bottom appeared to be a polymer of some sort. I assumed it was a veneer. If it isn't, I'm glad.

If you want to prove it to yourself you could always unscrew the base plate. I don’t have the experience to try that myself.

In any case, none of this detracts from the excellent review and comparison.

Edited August 20, 2022 by DavidGinMD

[Zeta Reticulan]

1 hour ago, DavidGinMD said:

If you want to prove it to yourself you could always unscrew the base plate. I don’t have the experience to try that myself.

In any case, none of this detracts from the excellent review and comparison.

I'll take your word for it. TBH I'm glad it is aluminium. Although, it wouldn't have necessarily detracted from the quality of the diagonal. The Tak' diagonal seems robust enough. Everything TV's built like a tank lol. I'm glad you enjoyed the review.

[Zeta Reticulan]

It's also worth pointing out that I can actually spell 'Everbrite'. ROTFLMAO!

[Zeta Reticulan]