Upgrading To A a Better Diagonal ?

[pat]

I received my Celestron 102mm f6.5 refractor. I've already read one review about upgrading to a better diagonal than the stock one. Would there be a much more visual improvement with these dielectric coatings? I use quality Tele-Vue eyepieces ect. from my 10" dob. The top useful magnification here is 100x with this scope. As far as I can tell, from observing sunspots and on one hazy night seeing about three cloud bands on Juptier. I haven't considered a 2" diagonal since all my eyepieces are 1.25". If a new diagonal is suggested are all makes/ brands about the same? Thanks for any help. Pat

[Capricorn]

A good diagonal would remove the potential problem of what you have being not so good. A diagonal needs to be flat and have a minimal difference between the peaks and troughs in the flattening, as well as good silvering and reflectivity. Concerning reflectivity I dioubt you could tell the difference between 99% and 90%.

The only one I am really aware of is William Optics diagonal. Not because there are no others just theirs seem to come up fairly often and what they say sort of fits the requirements. They say their SWANS are better at f/6 and slower not claiming perfections everywhere and they say their short ED's have well controilled CA not no CA. Sort of a realistic set of claims. Also WO seem to aim their products at being above average but at a reasonable additional cost.

Never heard of a TV diagonal, half suspect there is one as there may be a Burgess or Stellarvue or APM one, not sure if Skywatcher/Celestron offer a premium diagonal or not. In this respect all I can mention is therefore the WO offering.

Would have expected that you would have been able to drop a reasonable 5mm eyepiece in and got 132x, say a BST Explorer/Skyguider.

[pat]

When I use a good barlow on my 10" Orion, 185x is the limit. The same holds true on the 102mm. After 100x the image becomes soft. The weather here in southern Ohio doesn't cooperate. Pat

[John]

Tele Vue do indeed do diagonals in both the 1.25" and 2" sizes. They do ones with enhanced and dielectric coatings (96% and 99% reflectivity respectively). Dielectric coatings are more hard wearing than normal or enhanced ones as well as offering just a little more reflectiveness. The Tele Vue diagonals are superbly made as you would expect and, also as you would expect, rather expensive. The 1.25" goes for around £175 new and the 2" for around £250.

I have one of the 2" Tele Vues and also use a much less expensive 2" dielectric diagonal branded as Revelation but made by GSO. Optically the less expensive one performs as well as the Tele Vue although the build quality is not as solid. The Revelation / GSO 2" dielectrics cost around £90 new.

I've owned the William Optics 2" and 1.25" ones too and they are good diagonals performing as well as two I mention above.

Don't expect any of these to make a huge difference to the quality of your views. Subtle improvements though, perhaps.

[pat]

Thanks, John

It seems that since I sent this post I've had more time time to read other posts on this subject. It's almost as if I could put a blindfold on and reach into a bag and pull one out that works great. It seems that the one I have for this scope is a prizm. Whether it's coated I don't know. Or even if that would make a difference. I had thought I could get a sharper and brighter image or wider field in this small scope by going with an improved diagonal. Now I'm not as sure. Maybe the others sell because of their durability. So out of curiosity sake I might order one . Prizm or mirror seems to make no differance in this size and f/l scope? Thanks, Pat