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Good, Simple, Low Cost eyepieces for a C90

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#1 KarlL

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Posted 16 August 2014 - 04:38 PM

(If this belongs in the other forum, please let me know or move it.)

 

Any suggestions for eyepieces for a C90 (new production) (~ F/14) when doing solar, planetary, lunar, and double stars? Kellners? RKEs? I use an 8 MM RKE to great effect. (I must be the only person who doesn't mind the tight eye relief. :grin:)

 

Budget is a big concern.

 

Regards,

 

Karl



#2 nicknacknock

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Posted 16 August 2014 - 05:57 PM

A classic 8-24 zoom, a 32mm plossl and when finances permit, a binoviewer. You haven't seen the moon if you haven't used binoviewers on it...


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#3 PowellAstro

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Posted 16 August 2014 - 06:29 PM

The Agena Astro SWA 70 degree eyepieces at around 40-45 each are very decent for the price. Close to my Meades that were 3 to 4 times as much. The wide angle is nice as well. 


Edited by PowellAstro, 16 August 2014 - 06:30 PM.


#4 Don Taylor

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Posted 16 August 2014 - 07:28 PM

Astro tech Plossls - the value line ones are actually very good - same as GSO Plossls. Most FLs on sale for $23 each right now. Work great in my etx

#5 hardwarezone

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Posted 16 August 2014 - 08:16 PM

The expanse clone 20mm frames the moon well , sharp across 80% of the field but the outer 3% is bad.



#6 jaymcgil19

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Posted 16 August 2014 - 08:23 PM

Do a google search on this kit "Zhumell Telescope 1.25 Inch Eyepiece and Filter Kit"

 

John M



#7 jrbarnett

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Posted 17 August 2014 - 11:06 PM

(If this belongs in the other forum, please let me know or move it.)

 

Any suggestions for eyepieces for a C90 (new production) (~ F/14) when doing solar, planetary, lunar, and double stars? Kellners? RKEs? I use an 8 MM RKE to great effect. (I must be the only person who doesn't mind the tight eye relief. :grin:)

 

Budget is a big concern.

 

Regards,

 

Karl

Karl, I think this Vixen 3 eyepiece set for $140 is pretty nice for the C90:

 

http://www.optcorp.c...ce-package.html

 

A nice range in the C90 - 125x, 83x and 31x.

 

Regards,

 

Jim



#8 Traveler

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Posted 18 August 2014 - 01:22 AM

Yes the Vixen NPL series EP's are very good and also not that expensive. I use the 10 and the 15mm even with a F6 APO. 

Here is a nice review about the Vixen NPL line.

 

Btw. nice set did you found Jim!



#9 Hesiod

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Posted 18 August 2014 - 03:16 AM

I am not sure, you are searching for a replacement eyepiece or for a complementary one(s)?

 

I am not very fond of EP shorter than 7mm in my Synta 90/1250 (too dim); anyway, on few targets, I employ a 6mm BCO. Better purchase (IMHO) a 7mm* "Volcano Top", which is more comfortable than other flat-top eyepieces with tight eye relief.

 

As "low power" eyepiece a 32mm Plossl is a very good pick (a lot of brands offer that f.l. The Celestron OMNI line was not bad at all; other good ones are TAL and BCO. I never tried the NPL).

Otherwise you could look at 20mm-ish eyepieces, to get larger magnification and smaller exit pupil, which provides advantages under a light-polluted sky. The BCO18mm could be a great pick.

 

As for me, I use mainly a 8-24 zoom (but these are quite expensive), or a "set" made by 18mm BCO, 10mmBCO and 7mm Volcano Top

 

 

*another good choiche could be a 7.5mm "pseudo-Masuyama" like the Baader Eudiascopic, Orion Ultrascopic: branded-new are pricey, but there is a good number of them in the aftermarket (here yu could find even the Celestron Ultima, a now dismissed line)


Edited by Hesiod, 18 August 2014 - 03:17 AM.


#10 Patrick

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Posted 18 August 2014 - 11:44 AM

(If this belongs in the other forum, please let me know or move it.)

 

Any suggestions for eyepieces for a C90 (new production) (~ F/14) when doing solar, planetary, lunar, and double stars? Kellners? RKEs? I use an 8 MM RKE to great effect. (I must be the only person who doesn't mind the tight eye relief. :grin:)

 

Budget is a big concern.

 

Regards,

 

Karl

 

Televue Plossls are a safe choice, especially 15mm and above.

 

Patrick


Edited by Patrick, 18 August 2014 - 11:46 AM.


#11 caheaton

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Posted 18 August 2014 - 01:11 PM

A wealth of good suggestions in here.  In all honesty, the C90 with it's long focal length is easy on ep's.  Just about any ep will work well with it.  With that said, I'm fond of using  Astro-Tech Paradigms with mine...party because I keep the complete set (plus a diagonal) in a handy waist style pack purchased from telescopes.com (Orion makes a similar one).  It has room for every Paradigm in the series, a barlow* and room in the pouch for a diagonal.  It goes well with the portable nature of the C90.  Favorite focal lengths are the 25mm (about the same FOV as a 32mm plossl but with more magnification), 18mm (works well in light polluted back yard at giving a dark sky but without making the image too dark) and the 8mm (my choice for planetary observing).  On the moon I'm likely to choose the 15 and 12mm as they still have enough fov to frame the entire disk in the fov.

 

 

* Barlow generally not used with the C90, but I keep one in the case for use with shorter FL scopes.


Edited by caheaton, 18 August 2014 - 01:12 PM.


#12 Stelios

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Posted 19 August 2014 - 12:47 AM

Budget is a big concern.

 

If budget's a big concern, definitely buy used. I think 10mm, somewhere between 16-20mm and 32mm are the lengths you should be targeting. Unlike telescopes, you run much less of risk buying used EP's. 



#13 scopethis

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Posted 21 August 2014 - 07:03 AM

I use an old 12mm SMA (less glass) with my C90..the planets, Moon and open cluster are bright and sharp



#14 KarlL

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Posted 21 August 2014 - 10:33 AM

"SMA"?



#15 AhBok

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Posted 21 August 2014 - 11:56 AM

"SMA"?

Super Modified Achromat. It's a souped up Kellner.



#16 KarlL

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Posted 21 August 2014 - 02:19 PM

Randy -

 

Is it like an RKE? Where can I find SMAs? My 8MM RKE works quite well in the C90.

 

Regards,

 

Karl



#17 ChristianG

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Posted 21 August 2014 - 03:27 PM

Hi.

 

I have three Synta-made Maksutov telescopes (C90, 127 Mak and 180 Mak), all are between f/12 and f/15.

 

For these, 25 mm focal length with 60 degrees AFOV will pretty much maximize the true field of view (or a 32 mm Plossl with 50 degrees AFOV). That gives you the low-magnification end.

 

For high magnification, I found that these instuments can only go as high as about 35X per inch of aperture. An eyepiece with focal length in mm equal to the focal ration of the telescope will give 25X per inch of aperture. For the C90, that would be a 12 mm focal length eyepiece. For 35X per inch, an 8 mm eyepiece is fine. No need to go to any higher magnification.

 

The suggestion of a 8-24 mm zoom eyepiece is a good one, however bear in mind that zoom eyepieces have decent AFOV only at the smallest focal lengths, and only about 40 degrees AFOV at the longest focal length. I find this a bit narrow. A 8-24 mm zoom and a 32 mm Plossl could do, though.

 

Personally, when I assemble a small kit to go observing with my Maks, I bring three Agena Astro Starguider Dual ED 60 degrees AFOV eyepieces (same as Astro-Tech Paradigm): 25 mm, 15 mm and 8 mm. I have also used BST Flat Field eyepieces in the past, also available from Agena: 27 mm, 19 mm, 12 mm and 8 mm. All eyepieces are 60$-70$ each and are a very good bang for the money, the Dual ED being slightly better.

 

Explore Scientific 68 degrees eyepieces are nice, sharpness and contrast; the 24 mm could be a good choice for the low magnification. I sold mine, though: the 68 degrees AFOV is achieved through copious amounts of pincushion distortion, and the true field of view is about the same as the Dual ED 24 mm 60 degrees AFOV. For me, I find geometric distortion objectionable in an eyepiece, specially if terrestrial observation is on the menu. So I prefer the Dual ED and the Flat Fields over the Explore Scientific. Hope this helps!

 

--Christian


Edited by ChristianG, 21 August 2014 - 03:29 PM.


#18 Ed Holland

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Posted 21 August 2014 - 03:40 PM

If budget is a big concern, can you give us an idea of what you're willing to spend.

 

To set up my son's telescope, I tried out the SurplusShed Kellners (25mm, 15mm and 10mm), then about $15 each. They aren't bad, and I have used them in my scopes for planetary observation, where they seem to provide the best planetary detail of any of my other EPs. The 10mm is a bit tight in eye relief, but the others are comfortable to use, if one isn't concerned by the narrower FOV.

 

Just a thought,

Ed



#19 AhBok

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Posted 22 August 2014 - 08:42 AM

Randy -

 

Is it like an RKE? Where can I find SMAs? My 8MM RKE works quite well in the C90.

 

Regards,

 

Karl

RKEs are similar to Kellners and are sometimes referred to a "Reversed Kellners" due to the reversed arrangements of the lens elements. RKEs have a bit larger AFOV than Kellners. I had a set of the Meade MAs years back when plossls were the rage. MAs were reasonably priced and gave good on-axis images, though the AFOV was generally a narrow 40 degrees. I've owned a few RKEs over the years and found them to be somewhat more comfortable to use than MAs. They do give nice views, too.



#20 Usquebae

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Posted 22 August 2014 - 08:53 AM

The suggestion of a 8-24 mm zoom eyepiece is a good one, however bear in mind that zoom eyepieces have decent AFOV only at the smallest focal lengths, and only about 40 degrees AFOV at the longest focal length

 

I recently found a solution to this problem by using a 0.5x focal reducer.  Mine is Antares 1.25" and seems to work great with C90 and C6.  Screwed directly into a Russell 8-16 zoom EP the high setting on reducer seems roughly equivalent to the lowest setting native.  So I can get approximately 8-24mm from that EP, with 65 degrees at 16mm and at 8mm. 

 

For my Hyperion 8-24 zoom I can achieve a similar effect by screwing the focal reducer onto the tube from a GSO 2x barlow, then inserting the EP just as I normally would when using in barlow form.  This again seems to yield roughly the same mag at highest setting on reducer as at lowest setting native.  But instead of 43 degree afov at 24mm I get closer to 70 degrees, which should be max tfov.  I haven't measured any of this, just comparative viewing. 

 

A touch of vignetting may occur w/ the 8-24 on reducer but not enought to care about.  I don't know what the OP's mounting set-up is like, but I prefer the ultra-light Russell zoom (4.8 oz) with my C90 & DwarfStar because it balances perfectly.  If an 8-24 is workable it would offer a pretty full range of magnifications when accompanied by a properly spaced reducer lens.


Edited by Usquebae, 22 August 2014 - 08:57 AM.


#21 KarlL

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Posted 06 September 2014 - 10:01 AM

UPDATE

I purchased a Konus 20MM Kellner from Surplus Shed, and it is excellent. No color and sharp.

Thanks to everyone for great suggestions. That's something that makes CN great.

Regards,

Karl

#22 rmollise

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Posted 06 September 2014 - 10:53 AM

Plossls...and they don't need to be TV plossls. This scope is forgiving of eyepiece quality. Celestron's and Orion's plossls are more than good enough and can be had for around 25 - 50 bucks a pop. ;)

 

What do I use with my (orange tube) C90? That is anudder story... :lol:

Attached Files


Edited by rmollise, 06 September 2014 - 10:53 AM.


#23 DocFinance

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Posted 06 September 2014 - 09:44 PM

UPDATE

I purchased a Konus 20MM Kellner from Surplus Shed, and it is excellent. No color and sharp.

Thanks to everyone for great suggestions. That's something that makes CN great.

Regards,

Karl

I've gotten some good ones from those guys, but if you're going to use .965 EP there are still Vixen/Celestron Kellners out there like the ones that came with it.  They work just great in my old C90.



#24 Ed Whitney

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Posted 13 September 2014 - 04:04 PM

For high magnification, I found that these instuments can only go as high as about 35X per inch of aperture. An eyepiece with focal length in mm equal to the focal ration of the telescope will give 25X per inch of aperture.

 

This is a great formula! :)

 

I have found this to also be the case with my refractors as well.

 

The sweet spot always seems to be about 25x per inch of aperture. This equates to an Exit Pupil of 1mm which is as small as you should go anyway! :)  (unless the object is bright)

 

Thanks!








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