W.O. Durabright Diagonal ??????

[PlanetMan]

Can someone shed a bit of light on what is the difference/benefit (if any) between the William Optics 2" Durabright and their 2" Quartz diagonal?

Going purely by specs both have 1/15 wave flatness and 99% reflection - the only difference between the two is that the Quartz diagonal specifies a quartz based mirror whereas the Durabright states that it has a "15mm thick mirror"

So - I would like to know whether anyone has had any experience with a Durabright and could possibly explain whether/why a 15mm mirror is (or perhaps it isn't) any better?:thanx:

[UniPol]

I have both and to my eyes they are excellent diagonals. The 2" quartz has both the 2" slip in barrel and 2" SCT fitting whereas the 2" Dura-Bright cannot be fitted with the 2" SCT fitting.

If you read the following links I think your question may be answered :

http://www.williamoptics.com/diagonalPrism/stardiagonal_features.php

http://www.williamoptics.com/diagonalPrism/dielectricDB15_features.php

[PlanetMan]

Hi UniPol

I very much appreciate the feedback as I suspect both are excellent diagonals. I have looked at the links and once you get past the advertisement verbage the only real difference listed between the two I seem to discern is the following:

"high precision 15mm thick mirror substrate flat for optimal image stability."

So please correct me if I am wrong here but am I meant to take from this that a 15mm thick (presumably non-quartz) mirror in the Durabright is meant to be better than the WO quartz mirror diagonal?:thanx:

[blink138]

i am led to beleive that the quartz is a harder material than the glass and so can receive a much higher polish for reflectivity
could be wrong but!
pat

[gb_astro]

Just curious why the 2" SCT fitting cannot be attached to the Dura-Bright ?

gb.

[PlanetMan]

From my reading of the WO Spec's I don't believe it is an issue of the DURABRIGHT not being 'capable' but more that the SCT adaptor is not supplied (I could be wrong however).

The real mystery is what is the 'gimmick' so-to-speak about the DURABRIGHT versus the Quartz?

They were both originally priced the same by WO but now the DURABRIGHT has come down and is slightly cheaper than the Quartz so it would be nice now what is the angle or thought behind the Durabright with a 15mm thick mirror otherwise why wouldn't WO simply stick with producing their Quartz diagonals?:shrug:

As a point of pure speculation (inspired by the fitting) perhaps the thicker mirror is supposed to produce some sort of better output/optical performance with a refractor - pure guesswork here so please take this comment with more than a pinch of salt.

[UniPol]

The SCT fitting can't be attached as the 2" slip in barrel can't be undone, even WO says the SCT fitting is not supplied and can't be attached for whatever reason? Maybe the Dura-Bright is machined from solid?

When I get a chance I'll take the side plates off both diagonals and take a peek :eyepop:.

[PlanetMan]

Hi UNipol

I am keen to hear what you can observe about the DURABRIGHT.

I have done a little detective work of my own (as best as possible via specs and pictures on the net) and I have a tentative hypothesis about what may be the gimmick/angle/impetus behind the DURABRIGHT as opposed to the WO Quartz.

After looking at actual dimmensions of the diagonal housing I suspect the DURABRIGHT may be WO's attempt to challenge/copy the Televue 2' Everbrite diagonal which is also a non-quartz premium dielectric diagonal.

Looking at the actual shape/depth of the TV Everbrite housing and that of the DURABRIGHT - the structural depth seem roughly the same and although not specified the TV Everbrite may also contain a 15mm thick dielectric mirror.

Please take this as speculation.

[UniPol]

Hi PlanetMan,

You know what they say : "a picture is worth a thousand words" well here is a photo comparison between the WO Quartz & Dura-Bright.

The Dura-Bright is not bad value direct from WO at the moment especially with the US dollar so favourable. Here is the link :


http://www.williamoptics.com/wo_shop/catalog/product_info.php?products_id=545


I must thank you for your post as I found a brand new boxed Dura-Bright in my study, I don't remember buying it at all, I now have a spare.

[UniPol]

PM, I forgot to add that it might be worth while to have a look at the internals of various other diagonals as a comparison. I have a 2" Meade Series 5000, 2" Tak diagonal, 2" TeleVue Everbrite diagonal, 2" Bintel Quartz diagonal and 2" SkyWatcher diagonal. All work really well to my eyes.

[gb_astro]

So Steve can you see what's stopping the DuraBright nose piece from unscrewing?

gb.

[UniPol]

Hi GB,

The Dura-Bright 2" diameter slip in barrel may be locked in place with a retaining compound? I'll take the other side plate off tomorrow and see if the body has any locking grub screws.

I have tried to uncrew the barrel on the Dura-Bright but it won't budge. There must be an optical reason why the SCT adaptor can't be fitted but the reason certainly eludes me.

[robz]

Gee, that Dura-Bright glass looks suspiciously like the colour of plane old float/plate glass doesn't it?...............surely this isn't the case? :eyepop:

[Profiler]

Steve - This is really helpful stuff for everyone in getting to the bottom of diagonals (no pun intended) and whether we are potentially wasting our $$$ buying a big name brand such as Williams over the conventional and modestly price GSO.

You mentioned in your previous post that you had a range of diagonals - I am curious as to whether you could open up the Televue Everbrite and provide us with a picture alongside the William Optics diagonals and thus we can get to the bottom of planetmans hypothesis about whether the mirrors may be the same thickness????:thumbsup:

[robz]

I have the Bintel Quartz Dielectric and would be interested in looking at the ''guts'' too.

[UniPol]

Geez guys, only one disembowelling per day from now on if you don't mind :shrug:. I might as well dismember the Meade Series 5000 and Bintel Quartz but definitely not the Tak :mad2: diagonals over the following days just to satisfy those curious IISpacers.

Firstly, I took both side plates off the Dura-Bright and I would say that WO have used a retaining compound to lock the 2" slip in barrel or tightened it up so hard it can't be removed to attach the SCT fitting unlike the Quartz version.

Secondly, I have attached an image of the TV Everbrite, the mirror is around 10mm thick (a mm or so thicker than the WO quartz). It is set into the base plate as shown and has a fibre shim to hold it just in place.

* I'm going to ignore the comment about " float glass ", indeed!

Cheers everybody

[Profiler]

Steve - this is really interesting and helpful to us all but you have to wonder what are we all paying for in diagonals.

The Televue Everbrite is close to $400 and certainly not described as a quartz mirror - So asides from the solid one piece case we have to wonder what exactly are we getting in terms of optical performance for the extra $200 between over a Williams Quartz Diagonal and the Televue:shrug:

[UniPol]

Well, I've heard that the 99% reflectivity dielectric coated Bintel (ah la GSO et al) Quartz diagonal is up there with the best, who knows, but I have no complaints with the one I use on my Polarex/Unitron refractors. I use the Tak on my Tak's, the Meade on my Meade's, the TV on my TV's, WO on my WO's, SW on my SW's, Celestron on my Celestron's, pretty silly I know but that's just the way it is. Even if one tries to compare various brands/quality/cost the results would be so subjective for obvious reasons.

If you really want to see what effect/affect a diagonal makes to the optical train, just remove it and look straight through the eyepiece just like Gallileo (and the majority of Japanese amateur astronomers ?).

[PlanetMan]

Unipol - this really helpful and a rare opportunity to actually have a look at what we are all buying - Okay - it has been established that the DURABRIGHT has a thicker mirror than the WO Quartz and TV Everbrite.

Would you happen to have any insight/idea or be able to offer any suggestion as to why WO decided to make a diagonal with a 15mm thick mirror as opposed to simply sticking to their 2' standard dielectric and Quartz dielectric diagonals:confused2::confused2::con fused2:

[DavidU]

There is a great page here that explains why Quartz polishes so well.
http://www.fpi-protostar.com/quartz.htm

[PlanetMan]

I think everyone agrees that Quartz diagonals are very good but what I am very keen to know about is what is the idea or concept behind WO producing a 15mm thick non-quartz dielectric mirror diagonal. If there isn't any advantage or specific angle to it why would they bother making such a diagonal? Consequently, there has to be some sort of specific reason for the creation of the DURABRIGHT and I would be very interested to find out if anyone might know - It is not actually a cheap diagonal either - originally the durabright was the same price as the WO Quartz

[robz]

We appreciate your efforts Steve...............I was only playing around with the float glass comment:lol:

Rob.

[UniPol]

Well, I tend to think it may be a marketing exercise. WO will slowly sell off their Quartz stocks and the Dura-Bright will reign supreme.

I have attached a couple of pics again, the first is Bintel's and the second, Meade's Series 5000. The Meade is very well made, in fact you may notice that the mirror is housed in a metal pressing which is attached to the body with four screws (a pair either side). Both mirrors are 99 percent reflective and around 10mm thick.

Something which hasn't been mentioned before is the fact that the light path passing through the diagonal must be reflected at 90 degrees. Sounds obvious but some high end manufacturers such as Takahashi, TeleVue, Astro-Physics etc. go to great pains to obtain this and maintain this accuracy over time.

The next instalment in the series will be a 2" SkyWatcher and 2" Celestron diagonal.


* Come to think of it Rob, float glass has been used to make some pretty decent newtonian mirrors in the past, so why not mirror diagonals :thumbsup:.

[robz]

Thanks again for your effort Steve.:)

The Bintel is interesting isn't it?..............they have left the glass square with only the edges cut off at 45 degrees..........clever, cost effective.

As you mentioned that the G.S.O (BINTEL) diagonals are up there with the best of them, I'd say after my experience in using the dielectric quartz version, I would whole heartedly agree..........excellent value for money:).