Refractor diagonals

Starkler (Geoff) · #1 12-05-2007, 10:49 AM

I have just bought myself a refractor (Mortons Vixen ED115S) and will need to buy a diagonal for it. Looking for suggestions for a good quality 2" unit.

I have previously had an ed80 which I used with a WO mirror diagonal. It looked and performed nicely enough but I didn't like the tapered groove on the barrel, which gave the impression that tightening a screw against it would skew it out of alignment.

Can anyone speak for the quality of the gso made ones?
Any other suggestions?

Omaroo (Chris Malikoff) · #2 12-05-2007, 10:58 AM

Geoff - I bought a Bintel (GSO) 2" Quartz 99% reflective dielectric unit for $120 at SPSP for one of the WO 66mm refractors I have, which uses the SCT thread. The standard version has a straight barrel with a light groove - but not a deep dished one like the WO. It performs very well by all accounts, and if anyone can honestly tell the difference between it and my other - a WO, I'm a monkeys uncle.

Cheers
Chris

gbeal · #3 12-05-2007, 11:07 AM

I have the Baader/Zeiss 2" prism, and while it possibly weighs half of what your scope is (and maybe costs half as much as well) it is up there with the best. I have never regretted buying it, and it sees use on the ED80/840, as well as the bigger scopes.

casstony · #4 12-05-2007, 11:26 AM

The GSO's seem quite good but the Televue everbrite is certianly a step above. The Televue is lighter and generally better finished, including the function and construction of the compression ring. I can't give a critical assessment of the mirror. That said, I wouldn't be paying $500 for a new diagonal, and the GSO seems good enough. I had to remove the brass compression ring from the GSO and reshape it to fit proprly in it's groove.

JohnG (John) · #5 12-05-2007, 11:33 AM

I went all out and bought a TeleVue Everbright for use on my Takahashi FS-102, an excellent diagonal, very well made.

I also bought a BinTel 2" Quartz for use on my SW ED80 Pro, whilst the build is not up to TeleVue standard, the view through it is excellent, not that much different to the TeleVue, the only issue I have had is that the 2" barrel became loose, I fixed that by putting a drop of Locktite on the thread.

I suppose it depends on how much you want to pay, the Everbright is used on the FS-102 to enhance it's superb optics.

Cheers

JohnG

Starkler (Geoff) · #6 12-05-2007, 11:37 AM

Quote:

Originally Posted by JohnG

I also bought a BinTel 2" Quartz for use on my SW ED80 Pro, whilst the build is not up to TeleVue standard, the view through it is excellent, not that much different to the TeleVue,

This is good John. Can you please expand on " not that much different to the Televue"?
I understand the value of build quality etc, but I would like to know exactly what I would be missing with the view by going for the cheaper gso option.
Thanks

Starkler (Geoff) · #7 12-05-2007, 12:00 PM

Also can anyone explain why quartz is desirable over BK7 given that the rated surface quality spec is the same?

JohnG (John) · #8 12-05-2007, 12:17 PM

Hi Geof

I suppose the difference is subjective, I can tell very slight differences between the two when I use them on diffuse objects, mind you, I do use the same TV eyepieces on both diagonals. I get, no light scatter with the TV, the Bintel has the slightest bit of light scatter, not enough to bother you but it is there all the same. The BinTel gives nice pin point stars across the FOV, the TV also does the same although I suspect the star colours are more evident. Looking at the moon, I detect a very slight amount of reflected light, I suspect this is because of slightly inferior blackening.

But, saying what I said above, I would doubt very much, that people would really be able to tell the difference unless they did a side by side test, the BinTel is, in my opinion, good value for the money, the TeleVue is just that slight amount better, my opinion only.

Cheers

JohnG

Starkler (Geoff) · #9 12-05-2007, 12:51 PM

Thanks John, Chris, Gary, Tony

RB (Andrew) · #10 12-05-2007, 01:32 PM

I also use the TeleVue Everbright.
Sorry I can't offer a comparison, all I can say is I'm very very happy with it.
I use it in the SCT and refractor.

Prickly · #11 14-05-2007, 08:13 PM

Hi.

I have a vixen 140 neoachromat with a similar flip mirror assembly to your scope (I think). I bought a GSO dielectric diagonal. I find it quite wobbly and hard to secure in the vixen focusser. The standard focusser diameter if 48mm and the vixen is 49mm. This is not much difference but the GSO diagonal has quite a deep groove in it and I find the locking screws dont quite grip in (ie. not quite long enough). Perhaps not overly hard to fix but something to be aware of.

As for the optical quality mine seems quite nice but it is quite heavy and the problems with securing are presently an issue for me.

Just a warning. Suggest it might be worth trying a couple of diagonals out at star parties.

Hope you have lots of fun with your scope.

David

Starkler (Geoff) · #12 14-05-2007, 10:13 PM

Thanks David for the invaluable advice.

I don't have the vixen scope in my possession as yet. As it comes with the flip mirror I guess there's no rush to run out and buy a diagonal although it would be nice to use the 31mm nagler in it.

Prickly · #13 14-05-2007, 10:36 PM

No problems. The flip mirror (mine at least) is made in China. Nonetheless with my LVW eyepieces I get sharp images to the edge of field so it is quite good. You might want to try it out before you upgrade. (Doesn't take 2 inch eyepieces without the 1.25 inch barrel though of course).

Regards
David