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ebeyonder
member
Reged: 10/16/09
Posts: 45
Loc: Cambridge, MA, USA; Singapore
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Hi all,
I'm quite new to all this so would like to ask for your advice on my choice of EPs.
Right now I have a 26 mm, 9.6mm Meade Plossl and a 2x Orion barlow. I thought of upgrading from these and got the following just recently: Televue N13T6 and a Televue 24 Pan, as well as a Televue 2.5x Powermate.
Then I recalled reading that with the barlows/powermates, I should be careful not to duplicate focal lengths. It seems that with the TV24P and TVN13T6, I might well have done that - is this a mistake or is there any advantage to having these two EPs?
I am now looking for a high-powered EP to do planetary observation with. I wear eyeglasses and so am looking at the TV Radian line. I have narrowed my choices to the 3mm or 5mm. Taking into consideration of the barlow and powermate I have, which of the two would be better?
I currently have a ETX-LS (6"), LX90 8" and plan on getting perhaps a 80ED or 102ED refractor. I am currently in the US but will be going back to Singapore next year. Singapore is a heavily light polluted city, if that is factor.
Thank you very much for all your help. 
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Meade ETX-90, ETX-LS, LX-90 8"
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FLYcrash
member
Reged: 08/29/09
Posts: 96
Loc: Chicago, IL, USA
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Looking only at your recent TeleVue stuff (13T6, 24 Pan, and 2.5 PM), your effective focal lengths are the following:
24, 13, 9.6, 5.2mm
Not bad in terms of avoiding duplication/big gaps in magnification. I'm too lazy to look up the f/numbers or focal lengths of your scopes. 3mm is very short and may give excessive magnification. 5mm will nearly duplicate the magnification of your Powermated Nagler. So how about getting some eyepiece time with the 13T6 and Powermate and see how you like it? Then you can decide if you want more/less magnification, simpler designs, etc.
BTW, as the exit pupil gets smaller the need for glasses goes away due to the reduced effect of astigmatism in the eye. Even my girlfriend, who has a good bit of astigmatism, can use the highest magnification on my current setup (181x, 0.625mm exit pupil) without glasses and without complaint.
Edit: Also powermate the Meade 9.6 to get an effective 3.84mm eyepiece and see how you like that magnification.
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Raman
Young, myopic, non-astigmatic eyes; polycarbonate spectacles; Minox HG 8x33, 10x52 binoculars
Orion XT4.5 (114mm, f/8) Dob
Sirius 25mm, 10mm Ploessls; Vixen 17mm LVW; Orion Deluxe 2x barlow
Edited by FLYcrash (10/31/09 03:51 PM)
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ebeyonder
member
Reged: 10/16/09
Posts: 45
Loc: Cambridge, MA, USA; Singapore
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Very good advice, Raman. Many thanks and will give more time to the EPs first.
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Meade ETX-90, ETX-LS, LX-90 8"
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DNTash
scholastic sledgehammer
Reged: 09/02/07
Posts: 762
Loc: India
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I think the Radian is an excellent choice not only for your eyes, but for your ETX scopes in particular. I recall reading somewhere that it was in some ways designed for the Mak. It was my go-to EP when I had my ETX-90 -- ahead of my Nagler -- as the views were crisp and stable.
Either would be great. I'd get the 5mm and barlow it when necessary, given the options that you have.
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AT 72
TMB 92
Orion 120ST
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starrancher
professor emeritus
Reged: 06/09/09
Posts: 620
Loc: Northern Arizona
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Quote:
I think the Radian is an excellent choice not only for your eyes, but for your ETX scopes in particular. I recall reading somewhere that it was in some ways designed for the Mak. It was my go-to EP when I had my ETX-90 -- ahead of my Nagler -- as the views were crisp and stable.
Either would be great. I'd get the 5mm and barlow it when necessary, given the options that you have.
I could be wrong , but if you do the math , the OPs' currents scopes both have long focal lengths & even a 5mm ocular will yield 406X in the 8 inch & 305X in the 6 inch . At that point you are theoretically Maxed Out & to throw a Barlow into the mix is just way out there . OTOH if the future purchases of the two ED scopes were to come into the picture , you're still looking at a magnification that surpasses the theoretical limit on both of these using a 2X Barlow . Without doubling the power of the 5mm ocular it would indeed be a viable ocular producing 120X in the ED80 & 133X in the ED102 but using this short of a focal length eyepiece in conjunction with a Barlow on any of the above listed scopes is really not at all a useful situation . 
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LXD75 AR5
LXD75 SN8
Series 4000 Plossls
Misc. other stuff
Fort Rock , Az .
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ebeyonder
member
Reged: 10/16/09
Posts: 45
Loc: Cambridge, MA, USA; Singapore
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Thanks very much for all the advice. Much appreciated
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Meade ETX-90, ETX-LS, LX-90 8"
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