Diagonals?

[Astrosurf]

My head's spinning with the number of different diagonals out there! I've got a WO 72mm Megrez and wondered what would be a good one? What about Televue? They look a bit pricey though, unless I can get one second hand. The frac can take both 2" and 1.25" I would be using 1.25" EPs and also a webcam.

Alexxx

[alan potts]

Even a secondhand Televue is a bit pricey as they don't come up that often. I have them on my scopes and yes they are very good but I can't see any difference between them optically and the Meade 2 inch diagonal which I have now sold. The build quality it better but they are about 110 quid more so it has every right to be.

Televues do not come with a reducer from 2-1.25

I would get a WO diagonal, there have been a few S/H themselves lately. I think any in that area of 120-160- pounds will be very good and difficult to better.

Alan

[alan potts]

There is another thread on the go at the moment just down the page, not exactly the the same question but it is worth a read through to see what members say.

Alan

[Mark at Beaufort]

Alex I have a Televue Everbrite 2" diagonal which I got for my 4" Astro Tech frac. However, I recently bought a Revelation dielectric SCT fit 2" diagonal for my William Optics SD66 which is similar to this product from Telescope House - http://www.telescopehouse.com/acatalog/Diagonal_Dielectric_99__Quartz_LX.html

To be honest the view from both diagonals is the same so I wonder why I spent so much buying the TeleVue.

[Astrosurf]

Thanks guys.

Is this the 1.25" version of the Revelation you're referring to Mark?

http://www.amazon.co.uk/Revelation-Dielectric-Quartz-1-25-Diagonal/dp/B008JCCI1U

[cs1cjc]

Unless you intend to use this as a travel scope, so are constrained by weight, I would get a 2" diagonal. The GSO/Revelation quartz dielectric is very good value, I think.

[Naemeth]

Available from TH directly:

http://www.telescopehouse.com/acatalog/Revelation_Dielectric_99__Quartz_1.25__Diagonal.html

Whichever diagonal you choose make sure you go for one with 99% reflectivity. You don't want to lose anymore light than you have to .

[alan potts]

I have not seen that diagonal Mark, looks nice and sounds a lot cheaper than 250 quid.

Alan

[Mark at Beaufort]

Alex the one that I purchased was the 2" variety. In fact although I bought it for the William Optics frac I have since bought a 180 Mak and this 2" SCT diagonal fits this new scope and its brilliant. It is important that if you buy this diagonal I would recommend the 99% variety.

Mark

[Astrosurf]

Many thanks guys. Would the 2" deliver more light?

[Astrosurf]

I think I might go with this unless someone says, 'No! Go for the 2", it's much better!'

http://www.telescopehouse.com/acatalog/Revelation_Dielectric_99__Quartz_1.25__Diagonal.html

[Naemeth]

I'd actually go for the 2", you can always buy a 1.25" to 2" adapter if you really need it, a 2" to 1.25" may cause vignetting. In other words, the 2" will be more useful and future proof.

[billhinge]

I have a william Optic diagonal, I used to wonder about the expensive diagonals but given I'm happy with WO I guessed the difference was going to be very marginal

In any case if I use a camera I take the diagonal off so I guess the posh ones are purely vanity for visual - having said that my criticism of the medium price and lower ones is that the barrels often come unscrewed, I would hope a more expensive one wouldn't - whether its worth a lot more money I'm not sure though

I have had a cheap and nasty diagonal before,but spending a decent but not huge amount seemed to fix the optics if not the mechanics

wow - second time today this board created a double post - it wasn't me honest! (guess this site isn't idempotent )

[Astrosurf]

Yep, that's what I though people would say! I just hope I can find one second-hand.

[Ben Ritchie]

Optically I can't tell the difference between Revelation, WO, and Astro-Physics 2" diagonals; there is a difference in the quality of construction, but the Revelation is perfectly fine.

As for the 1.25" vs 2", the 2" does give some extra options and adapters for 1.25" eyepieces are cheap. But 1.25" diagonals are nice in a grab'n'go, lighter and more compact, and you don't really want the big 2" hand grenade eyepieces in a lightweight setup anyway. For my TV76 I just have a WO 1.25" and use a 24mm SWA for a max-TFOV eyepiece. More than enough. So depends what you want really, if light weight is an issue then nothing wrong with a 1.25"

[Astrosurf]

Well, I'd only use the diagonal for visual or with the webcam for planetary AP. I've only used the frac twice and am not very familiar with it but I had to borrow a friend's diagonal before I could achieve focus with the EPs and webcam. I've used it for DSLR AP and it doesn't need the diagonal. If the 1.25" doesn't let in less light then I'll save about £30 and get one of those!

[cs1cjc]

Many thanks guys. Would the 2" deliver more light?

The WO 1.25" CF diagonal has a narrow internal barrel (25mm) which significantly vignettes the view with wide angle 1.25" eyepieces, which may have a field stop of 27mm. I think that some degree of vignetting is inevitable with a 1.25" diagonal, but I do not know if it is a significant issue with the GSO. A 2" diagonal is significantly larger and heavier of course and typically more expensive too.

[knobby]

I've heard that too about vignetting.

I've not seen any on my W.O. 1.25" on a 127 Mak with a 32mm plossl or a 25mm exel lx

[M4lcs67]

Another vote for the WO. I bought the 2" Dielectric carbon a couple of months ago and it is a quality piece of gear. I like the adaptability of it and it comes with a 2" to 1.25" converter as standard for when you go 2".

[cs1cjc]

I've heard that too about vignetting.

I've not seen any on my W.O. 1.25" on a 127 Mak with a 32mm plossl or a 25mm exel lx

With an F/11.7, the vignetting will probably be too sharp to be visible, but you will not see the full eyepiece field. Instead the view is truncated sharply at a field stop of about 24mm. I used the following diagonal calculator, which is for Newtonians but works just as well in this context: http://www.siebertop...om/DIAGONAL.HTM

[E621Keith]

Many thanks guys. Would the 2" deliver more light?

No, but it will deliver more field. Some 1.25" may vignette the field

I think I might go with this unless someone says, 'No! Go for the 2", it's much better!'

http://www.telescope...__Diagonal.html

Go for the 2", not for optical reason, but for mechanical reason. 2" is mechanically stronger than 1.25", so it will allow you to use heavier accessories, such a wide angle or big zoom eyepieces with barlow. Nowadays, the only time I use my 1.25" WO is when the 2" optical path is too long and I don't have enough focuser travel.

[Astrosurf]

Thanks Chris. That will be useful.

EDIT: thanks Kieth, you just got in there before me!

I'm interested in a second-hand WO diagonal which I thought was like this:

http://www.williamop...CF_features.php

The guy's replied with this (he's Greek so his English isn't too good).

No, this is not my diagonal.It is the same quality (99% reflectivity) , but there is a diference at the diagonal body.

The one at the picture you send is a "carbon fibre" body, it is "sc" type, and there is an adaptor to switch the diagonal for "refractor" use (push fit).

My diagonal is the older model, (aluminum body) , and it is the "push fi" refractor type (fits only in 2'' drow tubes).

It it worth the £73 (inc P&P)?

[E621Keith]

There is a Antares 2" dielectric in Classified for £39.

I have one just like that. It uses set screw in 2" which is a bit annoying (compression ring in 1.25") and could used a little bit of flocking in the barrel, but otherwise it's a good diagonal. I am not sure I'd pay £73 for a WO when I can get a Antares for £39 from a reputable member, especially if the WO's seller is located in Greece.

[Astrosurf]

I think that, as I can't afford that much, I might well go for it. Michael Morris is a good chappy. I've just messaged him. Thanks for the heads-up!

[great_bear]

The WO 1.25" does vignette and also has reflections that are annoying on the moon.

A 2" diagonal helps avoid both issues, makes for a stronger eyepiece support, and also gives better optical quality.