Dielectric diagonals

[milkyjoe]

Hi all,

I'm considering upgrading my basic diagonal for either a wo or a tv everbrite, but my question is this: are they any good and worth the high price tag? (ok, that's two questions-lol)

Thanks

Richard.

[Capricorn]

If you mean is 99% reflectance significantly better then 95% reflectance then no. Your eye's will not be able to tell the difference.

The area of improvement may be in the flatness of the actual mirror. However unless then one you have is poor then again you will not be able to tell any difference.

The advantage is that you would have a good diagonal which would remove doubts abiut the performance. But at a price and they look good.

[milkyjoe]

Why do WO and TV sell these diagonals then if they don't make any difference, apart from to make money of course?! lol

[NGC 1502]

I think the same discussion applies to any piece of equipment, like the

1/4 wave, 1/6 wave, 1/8 wave, 1/10 wave debate with mirrors. It is the

law of diminishing returns, but for those who can afford the best, they

have the satisfaction that nice kit brings, plus when good seeing conditions

do eventually come, they are getting the best view thats possilble.

By the way, the mirror on my 10" Dob is rated as 1/4 wave, so I've no

axe to grind here !!

Regards, Ed.

[John]

I have a Tele Vue Everbright 2" but I'd say a Revelation dielectric (Telescope House - £85) is just as good optically. The Everbright is very well engineered out of a single block of alloy so it's a very solid foundation for heavy eyepieces.

[Ben Ritchie]

The only difference i've ever been able to see is swapping the el cheapo Meade 1.25" that came with my SCTs for a Revelation - that is a noticeable upgrade, because the stock Meade diagonals were quite poor quality, so I think if you only have a basic diagonal then upgrading is money well spent. But once you're into the mid-range (William Optics, Revelation etc.) then I agree with the others, it's very much diminishing returns to the extent that under any normal use I don't think you'd notice a difference.

FWIW I own 2" TeleVue Everbrite and 1.25" and 2" WO dielectrics, and can't see a difference between any of them and somewhat cheaper 2" Revelation or GSOs diagonals.

If you mean is 99% reflectance significantly better then 95% reflectance then no

I remember the standard Meade one being measured as 87% (7 years ago, so the bog-standard diagonals may have been improved). Going from that to the then-standard 'enhanced' (97%) was very visible. Back then 'dielectric' was mostly AP or TeleVue, but these days 'enhanced' has all but disappeared.

[Capricorn]

As John says the other aspects like the quality of build should be better. Possibly they are build so that you can get inside them easier to replace anything that breaks.

If you dropped it then maybe you can replace the mirror if it broke, on a cheaper one you may have to buy a whole unit. Note "maybe".

Usually it is for the general overall quality and if you had a 99% reflectance then you know you won't get more whatever you buy so you can stop wanting.

And a nice WO diagonal on a nice WO Meg looks good.

Use whatever you have and save towards a nice EQ5. The diagonal is the cost of the motors you will need. :D:D:D

And the motors will be more useful.

[Bigwings]

I have just upgraded to a Revelation 2". The prism 1.25 with the Nexstar SE8 wasnt bad but I do think the view is brighter with the upgrade but probably because of the greater light available from the SCT with the 2".

Other advantages with the SCT is that the diagonal screws onto the scope instead of a thumscrew so its more secure.

I can use 2" eyepieces.

I picked up mine new for £50 (ex bankrupt stock) otherwise I might not have been tempted.