Jump to content


Photo

Best eyepieces for Skywatcher 12"

  • Please log in to reply
22 replies to this topic

#1 Durden

Durden

    Explorer 1

  • *****
  • Posts: 55
  • Joined: 13 Aug 2013
  • Loc: Milton, Ontario Canada

Posted 18 September 2013 - 03:21 PM

Hello,

I'll thank everyone in advance for their input. I've recently purchased a 12" Skywatcher flextube dobsonian. Been loving every minute of it, but I've been wondering if I made some wrong choices with my eyepiece selection.

When I bought the dob I set aside what I thought was a modest budget for eyepieces, I told the sales person that I was interested in mostly deep sky, hence the 12" light bucket. I was told to get a Baader 31mm Aspheric, and the Explore Scientific 18mm 82*. I also have a 2.5x barlow, so with the 10mm and 25mm plossls that came with the scope, I have a pretty wide range of magnifications.

But I've been noticing that the Baader Aspheric seems to have a lot of coma or astigmatism? (stars off axis streak around the center)and the longer focal length seems useless because off axis isn't very pretty to look at.

Is my scope at 4.9 focal ratio too fast for this eyepice?
Are there certain eyepieces that are known to perform very well with my telescope? Should I be looking at putting some of my EPs on the used market and make a few changes?

Any recommendations in general about EPs would be greatly appreciated!! :)

Thanks!
Brian

#2 JackeShan

JackeShan

    Mariner 2

  • -----
  • Posts: 238
  • Joined: 18 Jun 2010
  • Loc: Sweden, Dalarna.

Posted 18 September 2013 - 03:41 PM

Explore scientific 82* eyepieces are very good value and shouldn't have any issues at your focal ratio. It's possible that 4.9 f/ratio is a bit much for Baader aspheric and is therefor showing more coma, but I haven't tried one myself.

I would just simply recommend more of the ES 82* series because of the excellent quality and the prices they are at now.

Welcome to Cloudynights :D

#3 kkokkolis

kkokkolis

    Vanguard

  • *****
  • Moderators
  • Posts: 2153
  • Joined: 23 Sep 2009
  • Loc: Piraeus, Greece

Posted 18 September 2013 - 03:49 PM

I have the same telescope and the Aspheric 31. You see a combination of astigmatism, coma and field curvature. I got a SW coma corrector to cure it but I haven't used it for a year because I decided it doesn't really bother me and I usually look at the center and mostly move the telescope, not the eyeball when observing. But since it bothers you, most similar eyepieces will show something, coma at least if they are well corrected for astigmatism. A Paracorr might solve that problem. But 10mm eyepieces (the 2mm exit pupil focal length) that you'll be using most of the time, don't show much coma. At long focal lengths a Nagler 31 will be better but you'll see coma there too. Personally, I'll get an ES82 30 soon but most times I use my 20mm ES100. Hyperion 31 is cheaper and much lighter than all these and most 30mm 2" eyepieces. It is great for SCTs and has a high throughput. Give it a second chance.

#4 JackeShan

JackeShan

    Mariner 2

  • -----
  • Posts: 238
  • Joined: 18 Jun 2010
  • Loc: Sweden, Dalarna.

Posted 18 September 2013 - 03:54 PM

At long focal lengths a Nagler 31 will be better but you'll see coma there too. Personally, I'll get an ES82 30 soon but most times I use my 20mm ES100.


How is the 20mm ES100 working as far as coma goes? I have the same telescope but haven't had a chance to do a first light with the ES100.

#5 Durden

Durden

    Explorer 1

  • *****
  • Posts: 55
  • Joined: 13 Aug 2013
  • Loc: Milton, Ontario Canada

Posted 18 September 2013 - 04:37 PM

Really appreciate the feedback guys. I will give the aspheric some more time. I just don't see the point in having a wide field eyepiece if you're only looking at the center, unless it's strictly a finder eyepiece or to keep an object from drifting completely out of view.

Again, if there are other recommendations for good EPs that are known to perform well in a scope like mine. Interested to hear how that 20mm ES100 is working out.

Thanks again!
Brian

#6 JustaBoy

JustaBoy

    Skylab

  • *****
  • Posts: 4356
  • Joined: 19 Jun 2012

Posted 18 September 2013 - 04:45 PM

In that scope I'd really like a 27 Pan.
-Chuck

#7 GeneT

GeneT

    Ely Kid

  • *****
  • Posts: 12790
  • Joined: 07 Nov 2008
  • Loc: South Texas

Posted 18 September 2013 - 05:59 PM

For my 12.5 incher, F5 I found the 31, 22 Naglers, and 13 Ethos and 10, 8, and 6 Delos to be excellent. I recently modified my lineup to a 21, 13, 8, 6, and 4.7 Ethos. I sold my 31 and 22 Naglers. I kept my 10, 8 and 6 Delos for some serious side by side tests with the Ethos equivalents.

#8 nevy

nevy

    Viking 1

  • *****
  • Posts: 608
  • Joined: 07 Feb 2012
  • Loc: UK

Posted 18 September 2013 - 07:05 PM

17 mm ETHOS.

#9 SeattleScott

SeattleScott

    Apollo

  • -----
  • Posts: 1399
  • Joined: 14 Oct 2011

Posted 18 September 2013 - 11:35 PM

How about Siebert Optical observatory series? 34 mm or maybe the 36mm if you are under 50. They are reported to have excellent edge correction yet they are light weight to eliminate balance problems. They cost about the same as your 31mm. Basically you get better edge correction while sacrificing eyepiece aesthetics and maybe coating technology. That is my understanding at least. Anything else you get with 30+ focal length and good edge performance at F4.9 will be expensive and heavy. 27mm Pan definitely an option too for a lighter weight option, but FOV is a little smaller than the others and it is still pricey.

Probably the best ones for edge correction at F4.9 are Vixen LVWs. At least in their 3.5 to 22mm range. Sharp to the edge in my F4.8. There is a 30mm but it is a different design and I can't vouch for it. That being said, my ES 24mm does awfully well at F4.8 but there is some edge distortion.

#10 Allan Wade

Allan Wade

    Messenger

  • -----
  • Posts: 499
  • Joined: 27 Jan 2013
  • Loc: Newcastle, Australia

Posted 19 September 2013 - 03:42 AM

Hey Gene, are you going to post your thoughts on the Ethos/Delos comparison seeing as you have similar focal lengths? I would be interested to know.

#11 kkokkolis

kkokkolis

    Vanguard

  • *****
  • Moderators
  • Posts: 2153
  • Joined: 23 Sep 2009
  • Loc: Piraeus, Greece

Posted 19 September 2013 - 04:36 AM

At long focal lengths a Nagler 31 will be better but you'll see coma there too. Personally, I'll get an ES82 30 soon but most times I use my 20mm ES100.


How is the 20mm ES100 working as far as coma goes? I have the same telescope but haven't had a chance to do a first light with the ES100.


Coma comes from the primary mirror's curvature, so all eyepieces show it, particularly those with wide true field of view, such as ES100 20 (or Ethos 21). Astigmatism is very low in ES100 20, less than coma and coma predominates (they give different star patterns). Overall it is a great experience.
Here how it goes with the SW 12". I put the ES100 20 and use it as a finder and observing eyepiece. For smaller deep sky objects I put ES100 9mm. Sometimes I put ES82 6.7 and rarelly ES82 4.7. When I use my filter wheel the ES100 20 doesn't come to focus. If I need to see extended objects like North America and Veil nebula, then I use Hyperion 31, otherwise Delos or Nagler T4. I just received the ES82 14, which I decided to get instead of the ES100 14, to save money/volume/weight/waiting time, since at this focal length I jump 2x and I rarely need something in between.

#12 coutleef

coutleef

    Skylab

  • *****
  • Posts: 4025
  • Joined: 21 Feb 2008
  • Loc: Saint-Donat, Quebec, Canada

Posted 19 September 2013 - 09:42 AM

the best ep i found was to first buy a paracorr

it made a difference with all the eps

#13 ibase

ibase

    Aurora

  • *****
  • Posts: 4582
  • Joined: 20 Mar 2008
  • Loc: Manila, Philippines 121°E 14°N

Posted 19 September 2013 - 11:58 AM

I just received the ES82 14, which I decided to get instead of the ES100 14, to save money/volume/weight/waiting time, since at this focal length I jump 2x and I rarely need something in between.


KKokkolis, by not getting the ES-100 14mm, you're missing half of your life! :foreheadslap: Joke. :grin:

Posted Image
14mm ES 100-deg & 82-deg

Tried my ES-100 14mm on a 16" Newt, and the majestic views wowed me and the astro-buddy who owned the scope; I think it will do as well on the 12" Dob.

Best,

#14 chuck56

chuck56

    Ranger 4

  • *****
  • Posts: 344
  • Joined: 21 Jan 2007
  • Loc: Chicago, Illinois

Posted 19 September 2013 - 12:52 PM

Baader Hyperions! Good bang for your buck!

#15 kkokkolis

kkokkolis

    Vanguard

  • *****
  • Moderators
  • Posts: 2153
  • Joined: 23 Sep 2009
  • Loc: Piraeus, Greece

Posted 19 September 2013 - 03:07 PM

I just received the ES82 14, which I decided to get instead of the ES100 14, to save money/volume/weight/waiting time, since at this focal length I jump 2x and I rarely need something in between.


KKokkolis, by not getting the ES-100 14mm, you're missing half of your life! :foreheadslap: Joke. :grin:

Posted Image
14mm ES 100-deg & 82-deg

Tried my ES-100 14mm on a 16" Newt, and the majestic views wowed me and the astro-buddy who owned the scope; I think it will do as well on the 12" Dob.

Best,


If it was smaller than the 20mm I would get it. I almost got one sometime ago. But I can use a barlow element I have to make the 20mm equivalent to 15mm with almost no weight gain and, since I had the older ES82 14mm (the same you have) and liked it, I decided to get the newer version that's easier to use.
Hyperions are good, but better with a 8" f6 and even better with a 6" f/8 (great at f/10-f/15 also). With 10"-16" f/4.5-f/4.9 one has to spend some more, perhaps for a Paracor.

#16 GeneT

GeneT

    Ely Kid

  • *****
  • Posts: 12790
  • Joined: 07 Nov 2008
  • Loc: South Texas

Posted 19 September 2013 - 03:17 PM

Hey Gene, are you going to post your thoughts on the Ethos/Delos comparison seeing as you have similar focal lengths? I would be interested to know.


Yes. Since Saturn is too low, I want Jupiter to be well above the horizon. I like to make these comparisons when either Jupiter or Saturn is in play, with some globulars and nebula and galaxies thrown in the mix.

#17 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 23167
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 19 September 2013 - 03:19 PM

the best ep I found was to first buy a Paracorr

it made a difference with all the eps

Good point. True for sure at f/5 or faster.
As for the visibility of coma, here's how it works:
Coma increases in linear size with distance from center. There is a very tiny region in the center of the field where coma is still smaller than the Airy disc, and this is the "coma-free" zone. This zone has a linear width of 0.0007" times the f/ratio cubed (0.01778mm x f/ratio cubed). Pretty small, eh?
And since the increase in coma is linear (i.e. twice the distance from center = twice the linear size), an eyepiece of 20mm with a 50 degree field will have comatic star images at the edge of the field half as big as a 20mm with a 100 degree field. This is true at every focal length--wider apparent fields see larger comatic star images.

Now, double the power of the 20mm 100 degree eyepiece to a 10mm 100 degree eyepiece. The field is 1/2 as wide. Does it see exactly the same size comatic star at the edge as the 20mm 50 degree eyepiece? Yes.
Alas, though, the magnification is doubled. So we see a comatic star 1/2 as wide, but at twice the power. Since 1/2 x 2 = 1, the apparent size of a comatic star image at the edge of the field will be the same at all focal lengths IF the eyepieces all have the same apparent field.

So coma doesn't go away at high powers unless your high power eyepieces have narrower apparent fields of view. Then, and only then, do the comatic stars diminish in apparent size.

So why do people say they see less coma at high power then they do at low power? There are some obvious reasons:
1) A comatic star image is brightest at the point nearest the center of the field and dimmer in its outer parts. Since a comatic star image has a size, it acts more like an extended object than a stellar point and the outer parts of the star image get dimmer with magnification, just like a galaxy.
2) We use high powers to look at small objects. We are not looking at star fields or large objects so we aren't examining the edges of the field. What coma is there goes unnoticed.
3) Many people use narrower apparent field eyepieces at high powers, so the linear (and apparent) size of the comatic stars are smaller.
4) Many more low power eyepieces have curved focal planes than high power eyepieces. Slight de-focusing of the star images at the edge, when stars are focused in the center, causes the comatic star image to appear even larger than it really is.
5) Many people have astigmatism in their eyes at low power that goes away as the exit pupils get smaller at high powers. This astigmatism stretches the stars but it has its greatest effect on the already-stretched comatic stars at the edge of the field. So the low-power comatic stars appear worse than the comatic stars at the edge of a high power eyepiece.

But if you view in dark skies, and all your eyepieces have the same apparent fields (or, maybe get WIDER at high powers), you will see coma at the edge of the field at all magnifications. And the best way to cure it is to eliminate it. The current model Paracorr keeps the size of the comatic star image inside the size of the Airy disc in a 40mm wide field stop (similar to a 31 Nagler) all the way down to f/3.5. So, in essence, coma is gone. The Paracorr also produces a mild field flattening effect, which might help those eyepieces with curved focal planes, too.

So your comment is apropos. It's likely more eyepieces will yield better images in the shorter f/ratio newtonian with Paracorr than without. That could save you money. And it certainly helps with the hyper-wide 100-120 degree eyepieces that are out now.

#18 JackeShan

JackeShan

    Mariner 2

  • -----
  • Posts: 238
  • Joined: 18 Jun 2010
  • Loc: Sweden, Dalarna.

Posted 19 September 2013 - 03:37 PM

Just a big thanks to Don for explaining coma. I always learn something new from your posts!

#19 Scanning4Comets

Scanning4Comets

    Markus

  • *****
  • Posts: 13776
  • Joined: 26 Dec 2004
  • Loc: Canada

Posted 19 September 2013 - 08:25 PM

If it was smaller than the 20mm I would get it. I almost got one sometime ago. But I can use a barlow element I have to make the 20mm equivalent to 15mm with almost no weight gain and, since I had the older ES82 14mm (the same you have) and liked it, I decided to get the newer version that's easier to use.
Hyperions are good, but better with a 8" f6 and even better with a 6" f/8 (great at f/10-f/15 also). With 10"-16" f/4.5-f/4.9 one has to spend some more, perhaps for a Paracor.

------------
Konstantinos


It's true that the 14mm ES 100 is a bit of a beast. I almost got rid of mine so I could get something a bit smaller, but then I put it in the focuser and almost slapped myself for even thinking about getting rid of it! :roflmao:

The views of M-42 were majestic with my Orion Ultrablock filter, plus I can use it on the double cluster and just fit it in for a closer view. There are several other targets it can be used on as well and the eye relief isn't too bad either. As long as you clamp the EP down good, there are no worries. :grin:

Also, a 14mm EP is a weird FL to find where you have nice correction and easy eye placement in a fast scope along with fairly good eye relief. The only other 14mm EP I know of that does that besides the 14mm ES 100 is the 14mm Denk or the 14mm Delos.

14mm Meade 4000 UWA- excellent correction, but kidney beans
14mm ES 82 - FC, uncomfortable to use (IMO)
14mm Meade 5000 - FC, bad edges
14mm Meade 5000 waterproof UWA - ZERO REVIEWS.
14mm Pentax XL/XW - FC - Excellent transmission & ER

Did I miss any other 14mm EP's?

#20 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 23167
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 19 September 2013 - 11:35 PM

Agena ED Eyepiece LER 14.00 1.25
Antares Speers-Waler LER SW 14.00 1.25
Arcturus ED LER 14.00 1.25
Bresser Modified Plossl Modified Plossl 14.00 1.25
Denkmeier Optical D14 Wide-Field 14.00 1.25
Desert Scopes Extreme View ED 14.00 1.25
Explore Scientific 100 Series Hyperwide field 14.00 2
Explore Scientific 82 Series UltraWideField 14.00 1.25
Harry Siebert Optics Performance + 14.00 1.25
Meade Series 5000 Ultra Wide Angle 14.00 1.25
Meade Xtreme Wide Angle Hyperwide field 14.00 2
Nikon NAV-SW Wide-Field 14.00 1.25
Pentax SMC-XW Wide-Field 14.00 1.25
Telescope Service Paragon ED 14.00 1.25
TeleVue Delos Wide-Field 14.00 1.25

#21 Deep13

Deep13

    Mercury-Atlas

  • *****
  • Posts: 2789
  • Joined: 25 Jan 2005
  • Loc: NE Ohio

Posted 20 September 2013 - 01:27 AM

I use a TV 27 Pan. without a Paracorr and it is sharp edge to edge.

#22 coutleef

coutleef

    Skylab

  • *****
  • Posts: 4025
  • Joined: 21 Feb 2008
  • Loc: Saint-Donat, Quebec, Canada

Posted 20 September 2013 - 05:48 AM

thanks Don

great explanation of coma in a dob.

now i better understand why i like my paracorr

#23 REC

REC

    Fly Me to the Moon

  • *****
  • Posts: 5352
  • Joined: 20 Oct 2010
  • Loc: NC

Posted 20 September 2013 - 07:59 AM

Yeah, the 13t6..... :lol:






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics