Televue Everbrite Diagonal

[Davesellars]

I've come into possession of a 2" Televue Everbrite.  As far as I can tell it seems to be the original version with a single set screw and unlike the current model it does not say "Televue Everbrite Dielectic"  instead in italics it just has "Everbrite" and there are no other markings elsewhere.   It does not have a 2" to 1.25" adapter.  The mirror is certainly in a very good condition and very clean.

I've had a look but I can't find much about the original version.  i.,e the quality of the mirror. Performance-wise would this better a modern mid-priced dielectric diagonal?

[John]

Sounds like one of the early Everbrights. They had coatings that were known as "Enhanced Aluminum" I believe. The performance should be very good with the difference being around 4%-6% reflectivity over one of the ones with dielectric coatings.

I have a couple of reasonably recent TV Everbright diagonals, one is the dielectic and the other enhanced aluminum. I can't recall noticing any performance differences between the two. I moved to the enhanced one a few years back from a Revelation / GSO dielectric. Again no noticable preformance difference but I wanted the 1-piece build of the Tele Vue unit because I had heavy eyepieces such as the 31mm Nagler.

 

[Davesellars]

Thanks John!  That's certainly re-assuring.  The build quality on these things is certainly solid!  I guess the main difference then would be in cleaning them being more susceptible to scratching?

[John]

I think that is the main benefit of the dielectric coatings - they are very hardwearing. I've not noticed my enhanced aluminum Everbright loosing it's edge though and I've had it for at least 5 years, probably more.

 

[Davesellars]

To be fair though aluminium mirrors used in scopes last an awfully long time. I would think that the deterioration in something like a diagonal would be very minimal. 

[John]

37 minutes ago, Davesellars said:

To be fair though aluminium mirrors used in scopes last an awfully long time. I would think that the deterioration in something like a diagonal would be very minimal. 

I agree. The dielectric coatings are more resistant to getting scratched by incautious cleaning I think.

 

 

[alan potts]

I like the build of the TV Everbrights but lets face it they are not cheap. As one would expect they work very well with TV eyepieces but the one thing that gets me is the no 2-1.25 reducer, it would not hurt them to put one in considering the cost new.

Alan

[Davesellars]

Very true. It's not like a decent 2" to 1.25" adapter is cheap either.

I didn't manage to test it last night on any stars or as was hoping the Moon as it was cunning hiding behind a bank of clouds playing very occasionaly peek-a-boo...    So instead I tried it out with a low power eyepiece (24mm) and a high power eyepiece (4.7mm) pointing at a distant television aerial and compared with my Skywatcher Dielectric that came with the 120ED.  At low power I couldn't tell any real difference between the two with the brightness and colour as expected both very sharp and bright.  At high power it did seem like the Everbrite was picking up a touch more while equally dim the sharpness of the image also seemed to be a little bit more than the Skywatcher being a little softer at this power to my eyes.

So the conclusion of this wholly unscientific test was while the coatings may differ very slightly in reflectivity (not enough to notice with this test) the TV Everbrite mirror is most likely more accurate than the Skywatcher Dielectric?

So it seems the diagonal is definitely one to keep... So now I need a 2" to 1.25" reducer (I was using my Skywatcher Diagonal's reducer last night).

 

[Timebandit]

10 hours ago, John said:

I think that is the main benefit of the dielectric coatings - they are very hardwearing. I've not noticed my enhanced aluminum Everbright loosing it's edge though and I've had it for at least 5 years, probably more.

 

 

9 hours ago, John said:

I agree. The dielectric coatings are more resistant to getting scratched by incautious cleaning I think.

 

 

 

Hello John. I hope the OP does not mind me asking a question slightly away from main post. But as you have had a lot longer being around quality diagonals than myself. What is the best way and approach for cleaning a dielectric diagonal. Up to now I have just either blown and dust off or using the Hoover nozzle close and sucked it clean. What is the situation with a cloth to wipe or something like Baader wonder fluid on the dielectric mirror. A step by step for best way of cleaning would be of Interest to me and hopefully other members possibility reading this. Thanks ☺

[John]

I've never needed to do more than blow dust from my diagonals. I'd not use the Baader fluid on them because it's not for coated mirrors as far as I'm aware. If there is a subborn mark I would probably try a "huff" of breath on the mirror surface and then a careful wipe with the Baader micro fibre cloth.

@Davesellers: Yes, I think the Tele Vue mirror is likely to have a better surface accuracy than the Skywatchers. There won't be much in it though.

 

[Davesellars]

Indeed I really would not see the need to touch the surface of the mirror even if it's a dieelectric.  OK, dust enters when you switch eyepieces but it's not like the thing's permanently open to the elements and likely to get other crud on it.

[Moonshane]

If it really bothered you then you could take it apart and clean it like a scope mirror but then you start thinking of things like diagonal collimation.  Puff away I'd say!

[Timebandit]

1 hour ago, John said:

I've never needed to do more than blow dust from my diagonals. I'd not use the Baader fluid on them because it's not for coated mirrors as far as I'm aware. If there is a subborn mark I would probably try a "huff" of breath on the mirror surface and then a careful wipe with the Baader micro fibre cloth.

@Davesellers: Yes, I think the Tele Vue mirror is likely to have a better surface accuracy than the Skywatchers. There won't be much in it though.

 

 

1 hour ago, Davesellars said:

Indeed I really would not see the need to touch the surface of the mirror even if it's a dieelectric.  OK, dust enters when you switch eyepieces but it's not like the thing's permanently open to the elements and likely to get other crud on it.

 

34 minutes ago, Moonshane said:

If If it really bothered you then you could take it apart and clean it like a scope mirror but then you start thinking of things like diagonal collimation.  Puff away I'd say!

 

Thanks Chaps. Better to ask first. And even though Baader wonder fluid is very good on lens IMO ,I did not think it was intended for a mirror (even though I am sure I read somewhere that some do use it , not sure results?) . But I think I will stay away from the BWF on the mirrors☺.  

As for taking the diagonal mirror out and collimation?. I dread to think what type of trouble I may get myself in and the angle it may go back in at ,and possibly the time it may take to adjust to set it back up collimated correctly( Happy to do my Dob reflector, but refractor and diagonal collimation i think I will leave to the experts) I think I will leave the diagonal mirror in situ, and if it needs more than a blow off or suction with the vacuum cleaner. I think I will use a piece of Baader cloth wrapped around a cotton bud and gently move across after a  huff  ?. Thanks guys I have learned something today and hopefully others reading this post will also☺

[Ben the Ignorant]

This will remove your doubt about the quality of a Tele Vue diagonal:

http://r2.astro-foren.com/index.php/de/12-beitraege/04-zweispiegel-systeme-astrofotografie/742-d052b-zenit-spiegel-der-feine-unterschied

Briefly put:

- Strehl (optical quality) ratio: 99% (impossible to do better)

- Peak-to-valley error in shape: 1/10th wave (excellent and within promised specs)

- RMS (polishing accuracy): 1/82th wave, only scientific ion-milled optics do better at 1/100th wave

When they make one that well, the others can't be a botched job. Keep that diagonal preciously.

[Davesellars]

Thanks Ben!

The previous owner said he bought the diagonal between 10 and 15 years ago (can't remember exactly).  It looks well cared for though with no marks apart from a few typical ones on the nose piece.

[Piero]

The TV Everbrite is a very good and solid diagonal. I have the 1.25" version and it does the job perfectly even when I used quite heavy combinations on it. Before I had a Revelation 1.25" dielectric quartz diagonal. Optically, they seem comparable, but mechanically the TV one is superior to me. I replaced my revelation because the screw thread on the eyepiece holder and the screw itself fell apart within few months after I bought it. It seems I was unlucky with this as many people praise the revelation diagonal very much. So possibly I had a faulty unit, which brings back the argument of the superior quality control by TV! 

Okay, to be fair I also have a faulty 20mm TV Plossl. It seems we owners of faulty TV gear are as rare as lottery winners, aside from the money in our pockets! 

Have fun with your new diagonal! It will surely work very well!  

[F15Rules]

Like John, I've owned both Everbright dielectric and enhanced models. Although the dielectric is supposed to be a few percentage points more reflective, I could never see a difference.

I sold both to invest in better eyepieces, where I CAN see the difference!

My current diagonals are both Revelation dielectrics (a 2" and a 1.25"), and I can't fault them optically..although there is no doubt the TV models are more robust: with the one piece body, I wouldn't use anything else for binoviewing -apart from a Baader T2 prism:-).

Dave

[Davesellars]

Out of interest how much would this be worth?  Like I said its age is around 10 years ish...

[John]

It depends on it's condition, optical and cosmetic. My guess is around £50 if it's generally in good order. The market is a bit obsessed with dielectric though so that might affect interest.

 

 

[Davesellars]

Thanks John!

[Davesellars]

By the way no way I'm selling it though...   It's too good!  I don't care about it not being dielectric if the surface accuracy is top notch.  These things cost a whopping £300 or so to buy now!

[Timebandit]

40 minutes ago, Davesellars said:

By the way no way I'm selling it though...   It's too good!  I don't care about it not being dielectric if the surface accuracy is top notch.  These things cost a whopping £300 or so to buy now!

 

Hello , that would not surprise me the way televues prices are going they are going astronomical?. But £300 for a TV diagonal?. As people are probably aware I have been a TV fan for a while but with the recent price hikes I am afraid I think it is getting hard to justify them, as there is kit just as good IMO in the market place. Look at the William Optics 2" dielectric diagonal for example. This has 99% reflectivity and a 1/12 lambda mirror and from the feedback i have seen people cannot see any difference in quality of view of more expensive diagonals and all for less than half price of the £300 televues . Obviously it is up to the person involved if they consider the televues one better??. Or maybe they are a televues collectionist?. But I think televues should have a look at their prices and compare them to the other quality in the market place. As IMO they could be losing market share because they may have the quality but people may see them as overpriced compared to possibly comparable products.  

[Davesellars]

I agree.  The TV prices (new) are very difficult to justify!  My only really expensive TV purchase has been my 14mm Delos.  An eye-watering price but I wanted 14mm particularly and there was not much else about (Pentax are now a similar price it seems...).  BTW, no way I would pay £300 for a diagonal!  As you say equally good performance can be had for a lot less £

 

[Pig]

I remember saying the same myself a few years back..... I wonder what helped me change my opinion  I guess it was looking through one that did it.

When all said and done they are expensive  

[Ben the Ignorant]

3 hours ago, Timebandit said:

 Look at the William Optics 2" dielectric diagonal for example. This has 99% reflectivity and a 1/12 lambda mirror and from the feedback i have seen people cannot see any difference

A friend asked me to star-test his old Genesis 101, which he left at my home with his 2" William diagonal. I did the test with his and my 2" TS (GSO) mirror which has the same specs on paper (1/12th wave). But the William proved a tiny bit soft, and last summer we star-tested a 130mm apo with the same  mirrors plus a Sky-Watcher (non-dielectric?) unit. Again, the William diagonal was less sharp than the others.

Anecdote: I spotted some 1.25" dielectrics at half the usual price at TS. I ordered two because I precisely needed these accessories: I had just bought two achros, one for me, and one for a friend's birthday. I compared them to each other and to my trusted 2" GSO mirror, plus the GSO 1.25" mirror always attached to my Celestron 5, couldn't see the slightest difference in definition or brightness. I could see a difference in sharpness and chromatism between the two achros, though, so you know I notice unequalities.

GSO quality and consistency are very good, from that test. But they do make mistakes: they had sent a batch of 1.25" diagonals to TS with plastic frames instead aluminum frames. That's why I could have this bargain, and make the comparo. The stock of half-price diagonals is long exhausted, though. Last word: the two plastic-frame mirrors needed collimation, while the two metal-frame mirrors needed none.