GSO Superview Ep's

Check out there specials page

http://www.atscope.com.au/specials.html

They have some on special there...not sure if it is what your after

[ausastronomer (John Bambury)]

Originally posted by acropolite
There's nothing in the Meade documentation to suggest that this is the case. The 2" diagonal is listed as suitable for all LX models including the 90. The Lx90 optically is identical to the 8' LX200.

Phil,

I am well aware that the OTA is the same as the 8" LX200. The same issues may also apply to the Celestron C8 and C9.25.

Do you really expect Meade to come out and tell you that there may be a problem here ? Come on, Meade have been copying other peoples designs and over exaggerating claims about their equipment for decades. Their latest one is their new RCX 400 which they claim is a "modified" Ritchey Chretien. By definition a Ritchey Chretien has a concave hyperbolic primary and a convex hyperbolic secondary. Meades new scope uses a spherical primary yet they want to put their hand up and call it a Ritchey Chretien, based on the success of this design by companies like Optical Guidance Systems, Parallax Instruments and RCOS. Meades Superwides introduced in the 80's were "very" similar to the Televue Widefields and the Meade Ultrawides were "very" similar to the original Televue Naglers, do I need to continue, or are you starting to get the picture of the company we are dealing with ?

I am not 100% certain that it is a problem, but I am about 80% sure that a number of people have minor issues using the 2" UO MK70 40mm in their 8" Cats. It is not the end of the world, you lose some light and stars at the EOF, but then why go to the low power widefield view if you dont get it all anyway.

I am merely trying to point out that this may be an issue before you part with your money. Try to get out to a star party and try out the components you are thinking of buying, even if its in a C8 or 8" LX200 or something, any CAT with a 1.25" visual back.

Clear Skies
John B

[[1ponders] (Paul)]

Phil if you check out on of strikers old eyepiece postings there is a link that lets you work out the amount of vignetting from different 2" eyepieces. From memory up to 35 or 36 mm there should be no problem but more than that then vignetting starts to affect FOv. That's with all of the meade SCT OTA's (LX models) You can get around it by changing the visual backing to one with a larger opening. I'll have a dig around and see if I can find the link

Here it is. The crossed out eyepieces are the ones that are most affected by vignetting.

http://www.petersonengineering.com/s...8_inch_SCT.htm

Check out the "Eyeopener" page for more info
http://www.petersonengineering.com/SkyDiv/EO.htm

[acropolite (Phil)]

Just had a look at that site Paul, thanks for that. John, it all makes sense now. The 8" LX opening on the back measures just under 2 inches, whereas the bigger meades have an opening that's 3". It's a minefield that's for sure. Is the field reducer useful for widefield or is it just for photography? Any recommendations for something in the 40mm range for widefield, or am I better to strap a refractor on top, or just forget anything larger than the standard EP.

[ausastronomer (John Bambury)]

Phil,

The maximum field of view of a 1.25" eyepiece is approximated with a 32mm plossl having an AFOV of about 52 deg. There is a formula, you multiply the AFOV by the focal length of the eyepiece and for a 1.25" eyepiece the maximum value is about 1650, for a 2" eyepiece it is about 2800. ie 32 x 52 = 1664.

The 24mm TV Panoptic also approaches the maximum FOV for a 1.25" 24 x 68 = 1632.

Al Nagler from Televue recommends a 32mm Plossl or 24mm Panoptic as the best low power eyepiece for use in an 8" SCT. In your scope a 32mm Plossl will give a TFOV of 50' or .83 of a degree. This isn't too bad when you consider your scope is not designed as a rich field scope. If you went that way the best eyepiece would be the 30mm Orion Ultrascopic for about $200 from Sirius Optics in Brisbane or the 30mm Celestron Ultima. These eyepieces are almost identical and offer superb image quality.

If you want to go the 2" route there is no reason you can't use a 2" 30mm eyepiece. Something like the 30mm GSO Superview (65 deg AFOV) would give you a TFOV of just on 1 deg. But a $200 diagonal and a 2" eyepiece is a big shellout when you could buy a far better quality 1.25" eyepiece for a slightly smaller TFOV.
If it was me I would be going with a 1.25" 30mm Plossl and be happy with what I have.

The SCT is a wonderful all round telescope it does a very good job of most things telescope, an excellent job of no things telescope, but wide fields of view is one of the areas the SCT is not seen at its best. Use your LX90 for the things it does best. If you want a Rich Field Scope buy one designed for that specific purpose like the Orion ST80. This scope would give a TFOV of almost 4 degrees with a 30mm 52 deg AFOV plossl. Horses for courses.

CS- John B

[acropolite (Phil)]

Thanks John, I'm pleased that I didn't rush in and order EP's with the LX. I can make an informed decision now. It would be nice to try out some EP's but I don't believe I have the opportunity in this area. The idea of a seperate wide field scope is attractive, especially as I can get double use as a spotting scope for HRH Liz who finds the Meade a little intimidating.

[beren]

Phils theres another angle to maybe give some consideration . A 6.3 focal reducer would save you money on purchasing longer focal length eyepieces plus serve a dual purpose if the astrophotophy bug bites in the future .When i was deciding on eyepieces getting the best eyepiece i could afford in the 20mm range was the catchcry for a F/10 scope. Ok i ended up with a 22mm nagler but team that up with a FR i just cant justify spending money on longer focal length eyepieces . If the budget is tight the stock meade 26mm plossl {one of my favourite eyepieces} with a FR might provide you with your low power setup, anywhy something to think about .

[trufflehunter (Wayne Robinson)]

Phil, I have the 2" WO diagonal on my LX90 and it is superb. A real work of art and worth every cent. Not only is it an excellent piece of optics, it's a nice bit of window dressing for the scope as well!

As far as 2" eyepieces go, currently I'm using the Meade QX 26mm (70deg FOV, MUCH better than the standard 26mm Plossl) and the 1rpd 30mm (80deg FOV). They both work brilliantly with the LX90 and there is no sign of vignetting. I'm waiting on a QX 36mm as well.

[trufflehunter (Wayne Robinson)]

woops! forgot to mention... make sure you get the SCT version of whatever 2" diagonal you choose to go with. Apparently some designs don't clear the fork base when the LX90 is pointing to zenith. The WO clears with about 2-3cm to spare.

[ballaratdragons (Ken)]

I am hoping that the Andrews 2" barlow called the 'Andrews GS 2" Barlow' is the 'GS 2" Barlow'. Has anyone bought that particular model.

[MiG]

Originally posted by ballaratdragons
I am hoping that the Andrews 2" barlow called the 'Andrews GS 2" Barlow' is the 'GS 2" Barlow'. Has anyone bought that particular model.

I have, and it is a 2" barlow from Guan Sheng optics. I hope that's helpful.

[ballaratdragons (Ken)]

Good, thanks Mig. Andrews is advertising them at $79.

I will have to get one, as stated in posts above the 20mm and 15mm SV's are only 1.25".

[janoskiss (Steve H)]

$75 from AOE, acc. to their website http://www.aoe.com.au.

[syzygy]

Hmmm, I use a 2" diagonal on my C8 with 55mm Plossl and 32mm Erfle eyepieces and no trace of vignetting at F10.

I seem to recall the Celectron's detailed specs for the scope quoted an unvignetted field circle 2.75 inches in diameter. Could the Meade's rear post opening be that much smaller?

Regards,
Chris

[acropolite (Phil)]

Wayne, Thanks for the feedback on the diagonal, which model WO did you get? Please let us know how the 36mm Qx performs when you get it. I am definitely going to get the focal reducer (thanks beren) which will be useful for my EOS as well. I hadn't considered the QX EP's but they seem very affordable. Anyone got any feedback on the 15mm Meade QX EP?

[trufflehunter (Wayne Robinson)]

I just got the standard WO 2", Phil, not the much more expensive dielectric variety. It's the SCT version that screws directly onto the visual back, replacing the original eyepiece holder. Ordered it from OPT. About $130US from memory, about $10US more than the Meade 2" model. Just realised too, I was a bit generous with my estimate of its clearance of the base of the fork arms... I said in my previous post it was 2-3cm... more like 15-20mm.

Yes, the QX's are great value in these scopes. I can't say what they're like in slower F ratios, however. I've become particularly fond of the 26. Nice wide field, sharp field stop, and only a very little softening of star images at the edge of the FOV... but only if you deliberately go looking for it. They're aren't too many ep's that don't suffer from that, even if you pay four times the price! I'll definitely let you know what the 36 is like when it arrives.