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Equipment Discussions >> Eyepieces

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Redshirt
member


Reged: 06/17/13

Unexpected viewing with the ES 24mm 68°
      #5938568 - 06/24/13 07:19 PM

I've spent the past few weeks trying out all three AFOV offerings by ES in a 16" f/5 scope. Overall a pleasant experience, particularly with the 100° flavor.

The most unexpected finding was with the 24mm 68°, which seems to get mainly great reviews. While I'm usually tolerant of a bit of field curvature, I found this EP's FC to be very annoying.

I was constantly reaching for the focuser knob to alternate between sharp stars in the middle of the field and the periphery. It was impossible not to notice the extent of the field curvature.

The amount of adjustment required to alternate between on-axis and edge-of-field sharpness was surprising. Has anyone else experienced field curvature with this eyepiece?


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Scanning4Comets
Markus
*****

Reged: 12/26/04

Loc: Ontario, Canada
Re: Unexpected viewing with the ES 24mm 68° new [Re: Redshirt]
      #5938666 - 06/24/13 08:28 PM

Wow!

I am so glad I read this! I almost ordered a 24mm ES 68 last week, but on the last whim, I ordered a 20mm Meade 2" waterproof 5000 UWA. I can't stand field curvature. My scope is a 10" F/4.7, so it would be even worse in my scope!

Thanks for the heads up!

Cheers,


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AhBok
professor emeritus


Reged: 12/02/10

Re: Unexpected viewing with the ES 24mm 68° new [Re: Redshirt]
      #5938675 - 06/24/13 08:34 PM

Yes, I found the 24 ES68 gave a lot of seagulls in my scopes. The 24ES82 performs splendidly, however.

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Allan...
sage


Reged: 10/24/12

Loc: Penticton B.C. Canada
Re: Unexpected viewing with the ES 24mm 68° new [Re: AhBok]
      #5938702 - 06/24/13 08:56 PM

I received my 24mm ES 68° two weeks ago and have not been able to use it yet due to clouds. I sure hope I didn't make a mistake with ordering (and waiting 6 months) it.

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GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Unexpected viewing with the ES 24mm 68° new [Re: Allan...]
      #5938709 - 06/24/13 09:05 PM

If it's like the Meade SWA 5000 24mm 68 degree it shouldn't be a bad eyepiece. I own it and it's pretty nice. I'll have to look for field curvature. May depend on the scope.

I've seen a lot of people compare it to the 24mm Panoptic and a lot of people prefer the SWA. Since you mentioned it I will give it a test in my refractor when I test my ES14mm 100 tonight. Will be a good comparison of similar fields of view.


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tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Unexpected viewing with the ES 24mm 68° new [Re: GOLGO13]
      #5938767 - 06/24/13 09:49 PM

I liked the ES24/68 so much that I sold the Pan24. Super sharp stars in center that continued all the way to edge, and this is in f/4.8 and f/5's. Maybe it's your mirror?

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Redshirt
member


Reged: 06/17/13

Re: Unexpected viewing with the ES 24mm 68° new [Re: tomharri]
      #5938813 - 06/24/13 10:16 PM

Quote:

Maybe it's your mirror?



It's just the one eyepiece that I was having the FC issue with, so I'm ruling that out for now.

I took a closer look at Bill's 24mm-26mm review, and he does mention some noticeable residual field curvature after using a Paracorr at about 80% from center FOV. Hard to say how much is there without the Paracorr as he groups other moderate-to-severe aberrations in at about 45%-50% away from center FOV.

24-26 mm Eyepiece Comparison

Perhaps a clue there, though. The other option is a bad egg...


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GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Unexpected viewing with the ES 24mm 68° new [Re: tomharri]
      #5938864 - 06/24/13 10:57 PM

might be a bad sample you have. Again assuming the same as the 24mm meade SWA. Mine is quite sharp almost all the ways to the edge in my 103mm F7.7 refractor. I will say the ES14 100 seems a bit better overall...but hard to do a comparison with the eyepieces that far apart.

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russell23
Post Laureate
*****

Reged: 05/31/09

Loc: Upstate NY
Re: Unexpected viewing with the ES 24mm 68° new [Re: Redshirt]
      #5939285 - 06/25/13 08:24 AM

Quote:

I've spent the past few weeks trying out all three AFOV offerings by ES in a 14" f/5 scope. Overall a pleasant experience, particularly with the 100° flavor.

The most unexpected finding was with the 24mm 68°, which seems to get mainly great reviews. While I'm usually tolerant of a bit of field curvature, I found this EP's FC to be very annoying.

I was constantly reaching for the focuser knob to alternate between sharp stars in the middle of the field and the periphery. It was impossible not to notice the extent of the field curvature.

The amount of adjustment required to alternate between on-axis and edge-of-field sharpness was surprising. Has anyone else experienced field curvature with this eyepiece?




The ES68's work great with my petzval refractor. The field seems pretty flat to me. But others have reported problems with edge performance using these eyepieces in fast dobs.

Dave


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russell23
Post Laureate
*****

Reged: 05/31/09

Loc: Upstate NY
Re: Unexpected viewing with the ES 24mm 68° new [Re: Scanning4Comets]
      #5939291 - 06/25/13 08:27 AM

Quote:

Wow!

I am so glad I read this! I almost ordered a 24mm ES 68 last week, but on the last whim, I ordered a 20mm Meade 2" waterproof 5000 UWA. I can't stand field curvature. My scope is a 10" F/4.7, so it would be even worse in my scope!

Thanks for the heads up!

Cheers,




Mark, I find the ES68's to be very consistent in performance. Since you didn't like the 28mm I'm sure you would have the same issues with the 24mm.

Dave


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Scanning4Comets
Markus
*****

Reged: 12/26/04

Loc: Ontario, Canada
Re: Unexpected viewing with the ES 24mm 68° new [Re: russell23]
      #5939364 - 06/25/13 09:25 AM

Dave,

You're more than likely right! Looks like my next purchase will have to be the mighty 30mm ES 82!

If it's anything like the Meade 5000 30mm 2" UWA, I'd like the 30mm ES 82!


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Unexpected viewing with the ES 24mm 68° new [Re: Scanning4Comets]
      #5940253 - 06/25/13 06:23 PM

Field curvature is worst in:
--refractors (especially short focal length refractors)
--short focal length newtonians (say, under 1000mm FL)
--SCTs

Refractors often have field flatteners available. SCTs (not the ACF or Edge) can be used with a f/6.3 reducer/corrector, and newtonians with focal lengths longer than 1000mm (39.37") are flat enough that the FC you see is probably in the eyepiece.

You can mitigate field curvature by focusing on a star away from the center and letting your eye accommodate for the center and edge. I used to do this with a TeleVue 35 Panoptic in my dob, and it worked well. Older people lack enough accommodation in their eyes sometimes, so this technique is not a universal one. It worked for me, though.


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rguasto
scholastic sledgehammer
*****

Reged: 11/18/10

Loc: Long Island, NY
Re: Unexpected viewing with the ES 24mm 68° new [Re: Starman1]
      #5940535 - 06/25/13 09:45 PM

I have noticed the field curvature also. It's the only eyepiece I own where FC is obvious. I find it a little annoying. Oh and its in my 8" F8 NEWT.

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Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Nyctophobia, Maryland, USA
Re: Unexpected viewing with the ES 24mm 68° new [Re: Redshirt]
      #5940652 - 06/25/13 11:14 PM

Quote:

I've spent the past few weeks trying out all three AFOV offerings by ES in a 14" f/5 scope. Overall a pleasant experience, particularly with the 100° flavor.

The most unexpected finding was with the 24mm 68°, which seems to get mainly great reviews. While I'm usually tolerant of a bit of field curvature, I found this EP's FC to be very annoying.

I was constantly reaching for the focuser knob to alternate between sharp stars in the middle of the field and the periphery. It was impossible not to notice the extent of the field curvature.

The amount of adjustment required to alternate between on-axis and edge-of-field sharpness was surprising. Has anyone else experienced field curvature with this eyepiece?




Thanks for this report. I don't have the ES 24 68° but every once in a while I think about getting one because - judging from many previous reports - they are the Poor Man's 24 Pan. Now that I know about the FC, I'll permanently delete it from my Wish List.

I have a 10" f/5 Dob. As Markus said, the FC should appear even worse in a 10" f/5 than your Newtonian, since FC is inversely related to focal length in these scopes.

So far I've owned an ES 100° 9, ES 100° 14, ES 82° 30 and an ES 82° 14. Among these eyepieces, the only one in which the FC was obvious to my eyes was the ES 82° 14. That was one of the few eyepieces I've ever sold because an aberration was so bad it actually proved an obstacle to observing. Even with a 1.9x OCS in a binoviewer, the FC was so terrible I had to refocus three times as Jupiter drifted across the FOV.

I have an ES 100° 20 on order now. I did not have any obvious FC problem with the other two ES 100° eyepieces, so I have high hopes for the 20mm.

Mike


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Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Nyctophobia, Maryland, USA
Re: Unexpected viewing with the ES 24mm 68° new [Re: Sarkikos]
      #5940657 - 06/25/13 11:22 PM

After reading through this and other threads on FC in eyepieces, I've come to the conclusion that the best test for FC in an eyepiece is a combination of a Newt with a long focal length and an observer who's eyes have poor focus accommodation (usually an old stargeezer). My telescope and I fit that description very well.


Mike


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Ernest_SPB
sage


Reged: 11/13/10

Loc: St.-Petersburg, Russia
Re: Unexpected viewing with the ES 24mm 68° new [Re: Redshirt]
      #5940870 - 06/26/13 03:14 AM

Quote:

The most unexpected finding was with the 24mm 68°, which seems to get mainly great reviews. While I'm usually tolerant of a bit of field curvature, I found this EP's FC to be very annoying.


According to my measuring eyepieces from 68-degree line of Explore Scientific have very moderate quality of field aberrations (curvature and astigmatism). Only 16 mm ep of the line has more or less balanced image quality at the edge of FOV, but it has very tight eyerelief.
The eyepieces could be recommended only for telescopes with slow F-ratio, like 1:8 and less.


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Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Nyctophobia, Maryland, USA
Re: Unexpected viewing with the ES 24mm 68° new [Re: Ernest_SPB]
      #5940896 - 06/26/13 04:33 AM

Ernest,

Define "very moderate." I can't wrap my mind around that idiom. It's like saying, "very lukewarm."

According to your measurements does the ES 68° 24mm have little, moderate or severe field curvature? Malenkii, ymerennei ili cilnei?

Have you measured the ES 82° 14mm? To my eyes, the FC from that eyepiece was severe.

Mike


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kkokkolisModerator
Carpal Tunnel
*****

Reged: 09/23/09

Loc: Piraeus, Greece
Re: Unexpected viewing with the ES 24mm 68° new [Re: Sarkikos]
      #5940915 - 06/26/13 05:19 AM

Last summer I tried a friends ES68 24mm on my SW 12" f/4.9, 66mm WO f/6 ED and SV 50mm f/4 finder. I aslo had my Hyperion 24mm and a borrowed Panoptic 24 and Vixen LVW 24mm. I found the ES far better than the Hyperion, especially at f/4, and almost as good as the TV and Vixen. There were some seagulls but I thought it was much more transparent than the Pan (the sky was very dark, 1600 meters high).
The result was that I bought the eyepiece from the man who loaned it to me and sold the Hyperion. I found Hyperion's views brighter than those of the Panoptic but the Pan had the better edges. My general feel is that the ES was a very nice eyepiece and I needed to use it on a f/5 scope with 1.25". I can can see somewhat bloated stars at the edge but no seagulls.


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Ernest_SPB
sage


Reged: 11/13/10

Loc: St.-Petersburg, Russia
Re: Unexpected viewing with the ES 24mm 68° new [Re: Sarkikos]
      #5940916 - 06/26/13 05:27 AM

Hm...
English is not my strong side.
For me "moderate" applied to aberration correction is in a middle between "good" and "poor". "Very moderate" correction of aberration shift evaluation to "poor" (bad).

Measures for 24 mm 68ES showed size of aberration spot near 20 angular minutes at edge of FOV in 1:4 scope. E.g. 24 mm Panoptic in the same conditions shows size of aberration spot less then 6 angular minutes.


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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Unexpected viewing with the ES 24mm 68° [Re: Redshirt]
      #5940933 - 06/26/13 06:21 AM

Quote:

Quote:

Maybe it's your mirror?



It's just the one eyepiece that I was having the FC issue with, so I'm ruling that out for now.

I took a closer look at Bill's 24mm-26mm review, and he does mention some noticeable residual field curvature after using a Paracorr at about 80% from center FOV. Hard to say how much is there without the Paracorr as he groups other moderate-to-severe aberrations in at about 45%-50% away from center FOV.

24-26 mm Eyepiece Comparison

Perhaps a clue there, though. The other option is a bad egg...




Dave:

What scope(s) are you seeing the field curvature with?

I own the 24mm Meade version of this eyepiece and I have used with a number of scopes, most quite fast. It's not a perfect performer in the NP-101 (101mm F/5.4 Petzval), there is some slight residual what I remember to be astigmatism, it's not a clean as the 31mm Nagler, but it is a very good performing eyepiece, there aren't many better.

I spent one evening comparing the 24 mm Meade SWA to my 20mm Type 2 Nagler in a 16 inch F/4.42 + Paracorr, it was close... it's a good eyepiece in a fast scope.

As far as the toughest test for an eyepiece, I think fast, flat field refractors like the NP-101 that are corrected for field curvature themselves are the toughest because they are essentially free of off-axis aberrations.. a fast Newtonian with a Paracorr is pretty darn good but they are not as perfect, there are some uncorrected aberrations.

Jon


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