Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

ES92 12mm & 17mm - good at f/5.4?

  • Please log in to reply
5 replies to this topic

#1 Blueox4

Blueox4

    Viking 1

  • *****
  • topic starter
  • Posts: 587
  • Joined: 26 Nov 2015
  • Loc: Upstate New York

Posted 22 May 2020 - 07:28 PM

I’ve got a Beautiful 13mm Ethos I have tried to like in my NP101 but have been underwhelmed. I wanted to like it as much as the 12mm ES92 I had but just haven’t been able to. In my 12” Dob the ES92’s were great. I’ve never tried them in my NP101 as I didn’t have it when I had them prior and Im wondering how they would perform?  I’m not sure if it’s the Ethos is a 1.25” eyepiece and the ES92 is 2” but I think I prefer the ES92’s. I’ve got a f/4 16” Dob coming in a couple months and I’d like to go back to the ES92’s but Only if they will perform well between f/4 In the Dob and f/5.4 In the NP101?


  • 25585 likes this

#2 Spikey131

Spikey131

    Apollo

  • *****
  • Posts: 1,345
  • Joined: 07 Feb 2017

Posted 22 May 2020 - 08:15 PM

1.  The 1.25” and 2” difference is meaningless.  The ES 92 12mm has a field stop smaller than 1.25”.  They could have made it a 1.25” EP, they just didn’t.

 

2.  I have a 13mm Ethos and an NP101.  I see a well corrected 100* 42x flat field.  The Pleiades and the Beehive look fabulous.  So does Orion’s sword.  What underwhelms you?

 

3.  I also have an ES92 17mm.  I like it, with the big eye lens and long ER, and I think that it is well corrected at f/5.4.  The downsides for me is the long eye relief and short eyecup, which allows stray light in.  It also does not take a Dioptrix, so I need to wear glasses to correct astigmatism.  Finally, the ES92 EPs weigh a ton and make the Ethos 13 mm seem light.



#3 CrazyPanda

CrazyPanda

    Vanguard

  • *****
  • Posts: 2,234
  • Joined: 30 Sep 2012

Posted 23 May 2020 - 12:55 AM

I’ve got a Beautiful 13mm Ethos I have tried to like in my NP101 but have been underwhelmed. I wanted to like it as much as the 12mm ES92 I had but just haven’t been able to. In my 12” Dob the ES92’s were great. I’ve never tried them in my NP101 as I didn’t have it when I had them prior and Im wondering how they would perform?  I’m not sure if it’s the Ethos is a 1.25” eyepiece and the ES92 is 2” but I think I prefer the ES92’s. I’ve got a f/4 16” Dob coming in a couple months and I’d like to go back to the ES92’s but Only if they will perform well between f/4 In the Dob and f/5.4 In the NP101?

For what it's worth, with a coma corrector in my F/4.5 dob (bringing it to F/5.175‬), my 17 ES92 is tack sharp right to the field stop. You'll most definitely need a coma corrector in your F/4 dob if you want to care about edge of field sharpness, so if you get a Paracorr, that makes it F/4.6, and I'm willing to bet that the ES92s work very well in a coma corrected F/4.6 light cone.

 

Before I got my coma corrector, the only aberrations I saw at the edge of the field in my ES92 was coma. If there was any astigmatism present at the raw F/4.5 light cone, it was considerably smaller than the coma produced by the mirror.

 

There will be no issue in the F/5.4 light cone of the NP101.


Edited by CrazyPanda, 23 May 2020 - 12:56 AM.


#4 Tank

Tank

    Skylab

  • *****
  • Posts: 4,157
  • Joined: 27 Jul 2009
  • Loc: Stoney Creek, Ontario, CANADA

Posted 23 May 2020 - 05:11 AM

At F4 and f5 I don't see problems with the ES92s
  • 25585 likes this

#5 25585

25585

    Cosmos

  • *****
  • Posts: 8,534
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the UK.

Posted 23 May 2020 - 06:00 AM

At F4 and f5 I don't see problems with the ES92s

Ditto. 

 

The 12mm needs to be 2" very definitely to provide the housing for its large lenses, that give the great views & easy eye relief.  


  • Ihtegla Sar likes this

#6 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 45,642
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 23 May 2020 - 05:40 PM

When the eyepiece is that large and heavy, it just is more secure to make it 2 inches for support in the focuser.

True, it could be 1.25", but I wouldn't want to put that mass into a 1.25" hole and have all that weight as leverage.


  • 25585 likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics