Which diagonal?

[Mike73]

I need a 2" diagonal for a 4" f/11 Lyra, I really dont want to break the bank with this but I'd like something which will do the Lyra justice.

I've read that Dialectric diagonal's are very good and this Revelation has been recommended to me but at £90 its really at the top of my budget.

I'm also about to place an order at TS, they have there own brand Dialectric diagonal and I've had a few TS brand products which have always been very good, has anyone got any experience with this one or should I just go for the Revelation?

[JamesF]

I do find myself wondering from time to time how much difference there is between diagonals as long as you keep out of the "cheap and nasty" ones.

James

[John]

I use one of the Revelation Quartz Dielectrics in my ED120 refractor. It's an excellent diagonal. In my other refractor I have a Tele Vue Everbright which is more than 2x the cost of the Revelation but I can't see any difference optically. The Tele Vue is beautifully machined from a single block of alloy though which makes it a really sold platform for my heavy eyepieces.

Apart from the slight increase in reflectivity, which would be unnoticeable I would think, the dielectric coatings are reputed to be more hard wearing and resistant to damage when being cleaned, than other coatings.

Another decent diagonal is the William Optics but they cost a little more than the Revelations I believe.

I have seen dielectric diagonals for around £70 but that's the lowest new price I've seen. I don't know what those are like.

[andrew63]

looking at your link - they could be the same diagonals - made in the the same factory in taiwan with just a different stamp on the cover. Might be worth looking on ABS as they come up often around the £50 mark.

andrew

[g0ibi]

I can the Williams Optics diagonal. I use it with my AA 6"RC and Meg 72 and get excellent viewing on both scopes!

Ron

[scarp15]

I use a 2" Revelation quartz diagonal in my C8 Mike, and the same as John really, I cant fault it.

[E621Keith]

It will be difficult to detect the optical difference between various diagonal mirrors, but the built quality can vary between brands. Some high end diagonal uses one piece construction so it is impossible for the nose piece to unscrew from the body. The nose piece in my Celestron do partially unscrew quite often when I use heavier eyepieces.

Another factor to consider is interior blackening. I own 3 dielectric diagonals (a Celestron, Stellarvue and Antares), while their performance on DSO are very similar, the Celestron has the least scatter for planets. This is probably because the Celestron has a matt black interior while the other two is slightly glossy.

You will need to see the diagonals in person to judge the level of blackening and built quality. I think these factors are more important to a diagonal's performance than whether the mirror is 98% or 96% reflective.

I have no experience with the TS or the Revelation diagonal. I have a 1.25" WO dielectric, the interior is well blackened and it is very well built. The 2" WO should be very nice as well.

[Mike73]

Thanks gents.

Its funny you should mention your WO 1.25" Keith as one of the reasons I was a little confused and started the thread was this review of the same diagonal left on FLO which I thought was strange as everyone else praises the WO diagonals? (btw I do know 1.25" isnt any good for me I was just reading the reviews ).

Still havent made my mind up but as the Christmas season is here and the shops are closed anyway it gives me a little longer to decide.

[E621Keith]

Thanks gents.

Its funny you should mention your WO 1.25" Keith as one of the reasons I was a little confused and started the thread was this review of the same diagonal left on FLO which I thought was strange as everyone else praises the WO diagonals? (btw I do know 1.25" isnt any good for me I was just reading the reviews ).

Still havent made my mind up but as the Christmas season is here and the shops are closed anyway it gives me a little longer to decide.

Interesting, I thought the WO is one of the better blacken diagonal. There are some shiny surfaces, but mostly inside the 1.25" eyepiece holder and the exterior, neither are visible to the light path once an eyepiece is inserted. The 1.25" nose piece on mine is well blacken, but I have not checked inside the housing. There is a internal safety stop but I have not noticed any problem with vignetting. I tend to use my 2" diagonal when I need the wide FOV, so may be I just haven't noticed it. The 1.25" nose piece is smooth and shiny, so it's hard for the focuser eyepiece holder to get a tight grip on it. When I use the 1.25" WO with binoviewer, it's very difficult to stop it rotating in the focuser.

I think many of these problems are exclusive to the 1.25" model and would not apply to the 2".

[John]

I've owned a William Optics 1.25" diagonal. Mine was well blackened internally but the thick internal ring that holds the drawtube to the body of the diagonal does slightly vignette eyepieces that use the maximum field stop size for the 1.25" barrel, eg: 32mm plossls, 24mm super wides etc.

[alan potts]

I have a TeleVue 2 inch diagonal and a Meade 2 inch, I have looked through the same one you are asking about many times and if I am honest I can't tell them apart optically, only by biuld quality. I would buy one.

Merry Christmas, Alan.

[stuartjones]

Hope no one minds me butting in here but it seemed the ideal place to ask a quick question about diagonals, my new scope is a 2" eyepiece holder and I have a 1.25" adapter but i need a diagonal for the scope. what would be best to do Buy a 2" diagonal and use the adapter after it or a 1.25" diagonal and put it on after the adapter or would it make no difference. again hope i have not offended anyone butting in here .

Many thanks stu

[John]

I don't think the Skywatcher 1.25" adapter will work with in 2" diagonal as they are specifically designed to fit the drawtube of the scope. A 2" diagonal should come with a 1.25" adapter of it's own. You would then put the 2" diagonal into the 2" eyepiece holder of the scope and use the diagonals 1.25" adapter to hold 1.25" eyepieces and remove it if and when you use 2" eyepieces as they fit straight into the diagonal. Basically, if you buy a 2" diagonal, the 1.25" adapter that came with your scope would become redundant.

Hope that makes some sense and answers you question and that I've understood your question !

[stuartjones]

When I purchased the scope I had no diagonals or adapters with it this is how i managed to get the scope within my budget as he was selling it with these bits missing.

But yes what you say makes sense to me, I just did not want to ruin the quality of the optics by putting the adapter or diagonal in a combination that would make the optics of a lower quality.