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Long ER eyepieces


horseheadnebula
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I have had Orion XT10 intelliscope (1200mm focal length / 254mm mirror / f 4,72) over a year now with two Orion Sirius plossls eyepieces (10mm and 25mm) which came with the telescope and now would be time to upgrade new eyepieces.

10mm plossl is useless for me as I need to wear eyeglasses due to astigmatism. So I badly need new eyepiece in higher magnification area. 25mm is somewhat usable, I cannot see entire field stop, if it is right term, unless I push eye and glasses onto eyepiece which means glasses might get bit dirty. Manufacturer list on their website that 25mm eyepiece have 16,9mm eyerelief so it would be nice to have couple mm more eyerelief.

Right after I bought this telescope I borrowed some Baader Hyperion & Aspheric and Orion Epic eyepieces. Back then I was totally newbie with telescopes and eyepieces but noticed that Hyperion was comfortable to use but Aspheric had horrible views around the edges. Later I read that it is some sort of aberration, maybe astigmatism. This was surprise as Aspheric is quite expensive eyepiece. So I started to read information about eyepieces and ended up into this very nice forum and looked eyepieces like Pentax xw and Delos.

As with student budget I'm not exactly rich but I think that quality eyepiece would get years of use so I could buy one or two good eyepiece per year. Atm my budget would be couple eyepiece in Pentax / Delos price range. 

I read somewhere that eyepiece with 2mm exit pupil would be most versatile eyepiece. Is it so and would it be good focal length for first eyepiece? If it is then many have praise 10mm Pentax xw and that would be probably best in xw series. But in longer focal lengths some other manufacturer would be better. And if 14 or 17mm would be more practical all-rounder Delos might be good choise.

So I guess my question is which one or two focal lengths would be best starting point?

It might be that I order one eyepiece at first and look how it performs.

I have also looked astro buy & sell site. At the moment there would Vixen LVW 5 & 8 mm and Vixen SLV 6mm. Those seems to be good eyepiece as well and are parfocal with Pentax xw (which is very nice) to my knowledge. There is also Televue nagler 17mm type 4, even 17mm eyerelief is bit tight and it might be annoying to have 1,25" and 2" format but second hand it wouldn't be so expensive. Also there is Pentax xw 5mm but even it would be nice pair with xw 10mm maybe it is too much magnification and less usage. This is more theoretical speaking as I haven't checked yet would any of them send outside to UK.

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I have looked at the Tele Vue Delos Range,  with their 20mm eye relief ( I was thinking of a possible future upgrade to my telescope,   larger aperture -  faster focal ratio ) and they are also compatible with their Dioptrix  system, which compensates for astigmatism, and supposedly better than wearing glasses alone?

http://www.televue.com/engine/TV3b_page.asp?id=54#.VhkFkPlVhBe

Edited by Charic
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I use the Nagler 17T4 with glasses without issues. Great EP and very versatile. I also have a Pentax XW10 and it is superb. The 8mm Delos I have is its equal, but isn't parfocal with it.

Sounds like all are nice eyepieces. Do you mean that Delos isn't parfocal with Pentax xw but 17T4 is (at least somewhat) parfocal with Pentax? Would that Pentax xw 10mm be good choice for first eyepiece? And how about if I order two? Is 10mm and 17mm better pair than 10mm and 14mm (along with somewhat usable 25mm plossl)? I could also buy 2 x focal extender and also get 5mm and 7mm or 5mm and 8,5mm. 

I have looked at the Tele Vue Delos Range,  with their 20mm eye relief ( I was thinking of a possible future upgrade to my telescope,   larger aperture -  faster focal ratio ) and they are also compatible with their Dioptrix  system, which compensates for astigmatism, and supposedly better than wearing glasses alone?

http://www.televue.com/engine/TV3b_page.asp?id=54#.VhkFkPlVhBe

You are probably right that Dioptrix would be better than glasses but I'm practically blind without glasses and need them while reading star charts etc. Though it would be nice to try it with Explore Scientific 100 degree eyepieces and feel the spacewalk experience! I have read that someone use dioptrix with those and ES eyepieces wouldn't cost Ethoses. But I don't know how practical this kind of system is.

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Most of the Delos will reach focus a good 8mm or so further out than the Pentax XW's do. The 17.3mm and 14mm Delos have different focal points though which are around 12mm futher in than the other Delos models and somewhat closer to the XW focus point.

I've used a Pentax XW and it's a superb eyepiece - nothing to pick between it and the 10mm Delos in my opinion. 

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The Delos 17.3mm would be a killer EP for hunting down DSO's and would probably end up as a workhorse EP.   It's FOV would be only slightly smaller than the 25mm Sirius plossl that comes with the XT10.   However it would be somewhat redundant with the 25mm.   If your 10mm ER is too short to use comfortably, then probably that would be the EP to replace first.   You mentioned the 5mm, 6mm  and 8mm Vixen EP's.   Those are all good.  I think you would get most use out of the 8mm.    All of the Pentax XW's or Delos EP's are good and you can't go wrong with any of them.   Other options are the new Baader Morpheus EP's. They've gotten good reviews and they are  a little less expensive than the Pentax or TV EP's.  The Starguider EP's are even more less expensive.   These are pretty good, but they will  get a bit sloppy at the edges.   I use them with my Z10 (F 4.9), I like them, but you will see a little more sloppiness at the edges with  a 4.7 scope

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  • 2 weeks later...

Thanks everyone from answers. Seems quite hard to decide which focal lengths would be best. There is lot of good focal lengths between 8-17mm but I think I settle on 10mm and 14mm. I also emailed to Firstlightoptics and Steve suggested these FL. I would get with 2 x focal extender:

14mm / 7mm = 85x, 170x. (2,96 exit pupil with 14mm)

10mm / 5mm = 120x / 240x. (2,11 exit pupil with 10mm)

Those new Baader Morpheus EPs looks promising. Still probably would be wise to wait John review and decide after that which 14mm I´ll buy. I have read that 14mm Pentax xw would have some field curvature. How bad it is actually? Is it reason not to buy it?

At the moment in my shopping basket is

Pentax xw 10mm

Rigel finder

Premium cheshire

Celestron Lens pen

Either Bresser SA barlow or Explore Scientific 1.25" 2x focal extender

Star map

I think it is good starting packet and will buy other EPs later.

The Nagler 17T4 isn't parfocal with my XW10, as far as I can see. However, it is a 2" EP, unlike the XW. Much will depend on the 2"-1.25" adapter.

Yes it is 2" Ep and that's why I decided to not to buy it. For some reason I have bought second hand 1.25" Lumicon UHC filter and wanted to use it with new EPs. Even though I haven't really seen anything with it but wanted to give it second chance with better EPs. Also it would be cheaper to buy 1.25" than 2" focal extender. But that second hand 17T4 was sold quite cheap price so hopefully my decision wasn't bad.

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I have the SkyWatcher equivalent of your scope and like a decent amount of eye relief.

I'm happy with my collection barring a hankering after a Ethos 21mm at some stage (breaking my own eye relief rule)......

- 50° Vixen 6 & 5mm for High Mag (the 5 doesn't get much use due to UK sky! You get much more use from 200x than 240x)

- 72° Delos 8, 12 & 17.3mm (all great but 17.3mm non parfocalness is a minor irritation)

- 82° Explore Scientific 24 & 30mm (30mm needs dark dark sky to really fly)

Hope that this helps.

Paul

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  • 3 months later...

Four months and still undecided :S

Many of you who have posted in this thread seem to have 8mm and 12mm rather than 10mm eyepieces for 10 inch dob. Would 8 and 12mm be better "base line" than 10mm and 14mm?

If using 1,4x factor rule and one would have 12mm eyepiece he would get 6,1mm - 8,6mm - 12mm - 16,8mm and 23,5mm focal lengths eyepieces. Now if I add 17mm eyepiece and 2 x tele-extender I would get 6mm - 8,5mm - 12mm and 17mm. Then some 24-31mm. Sounds like a plan? 

Let's say if I had 92 degree apparent field of view with new Explore Scientific 12mm ocular and  barlowed to 6mm, it would have 0,46 degree true field. Would it make any sense to buy for example 7mm pentax xw with 70afov? It would have less true field (0,41degree) than 6mm ex.sc (or same true field than barlowed 12mm nagler with 82 afov).

Maybe I should add that probably I have enjoyed most to watch globular clusters. Would that 8,5mm be too much for M13? So should I consider 10mm after all?

Anyone have experience about new Explore Scientific 92 degree eyepieces? Looks very promising with decent eyerelief. Atleast in Cloudy nights forum there is some hype. Only quite expensive.

http://www.bresser.de/en/Astronomy/Accessories/Eyepieces/Explore-Scientific-92-LER-Eyepiece-17mm.html?listtype=search&searchparam=92

 http://www.cloudynights.com/topic/528192-new-explore-12mm-92-degree-is-in-game-changer/

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2 hours ago, horseheadnebula said:

Four months and still undecided :S

Many of you who have posted in this thread seem to have 8mm and 12mm rather than 10mm eyepieces for 10 inch dob. Would 8 and 12mm be better "base line" than 10mm and 14mm?

 

........my base line (now) is the 6mm, it matches the focal ratio of my f/6 scope, a good starting point for my short focal length eyepiece. A 12mm could have been just as good, as it seems to give me a sweet spot when observing, and could still be 2x Barlowed to produce  200x power, which this scope is capable of producing.

Not sure if you can get a  4.7 or 4.8mm EP for your scope,  but a 5mm would be a good  base line for a 10" scope. Its just a matter of choice/ taste, also an  8mm and  10mm at 2x Barlow would work  either-side of your focal ratio
I own several eyepieces, and the one  that gives me the best view  is the right one to use.  If  it looks good, it is good. (when the weather allows :angry8: )

My first upgrade was an 8mm  Starguider, 60°afov with about 13mm eye-relief, Its very comfortable to use.
My recent additions,  the Delos, were  collected in order to match my new 12" or 10"  Skyliner? ( still waiting )  They would work well on your faster scope, given that their  designed to work at f/4 and slower, their field of view would be wide enough, the eye-relief  adequate at about 20mm. 

 

Edited by Charic
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I wear spectacles for astigmatism and all the eypieces in my signature are comfortable to me in terms of eye relief, give views that vary from good to superb and vary is field of view but all have a place depending on what I am viewing from double stars to nebula or globulars to galaxies and open clusters.

 

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Thanks for your response. I ordered 8mm Delos. It helped the decision that there is bit discount on Deloses in http://okularum.eu.

bomberbaz, good to know that eye relief in Nagler 26mm and Nikon 17hw is enough. I would have assumed 16mm eye relief is bit tight with spectacles. Not that I could afford for Nikon but I could looking for second hand Nagler.

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20 hours ago, bomberbaz said:

16mm ER is the limit, it is this that stopped me getting a 21mm Ethos. The Nikon takes some getting used to and I am still adapting but each time I use it I start to love it just that little bit more.

My experience too.

I do have a hunch that it kind of dependend on AFOV too, up to about Nagler's 82 degree, 16mm might be enough. But for 100 degree EPs, glasswearer might need a couple of more mm ER. 15mm ER should be plenty for none-glass-wearers(Nagler T6 has 12mm ER, which work very well for many none-glass-wearers) , but there are quite many have difficuty with 100 degrre EPs' 15mm ER.

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20 hours ago, michael.h.f.wilkinson said:

My experience too: 16mm is the minimum, 15mm and you keep nudging the EP with your glasses. I have used a 26mm Nagler (Olly's) and it was fine. The 14mm Meade Series 5000 UWA (mk1) was just a touch short, as was Olly's 13mm Ethos.

 

I think that acceptable eye relief for use with glasses varies more than this indicates.  

Eye relief, as I understand it, is the distance from the eyepiece where the light rays cross for a point on axis.  In fact the rays for a particular point on the image come in as a parallel bundle, generally referred to as the exit pupil.  See the diagram at: http://www.telescope-optics.net/eyepiece1.htm.  Suppliers generally quote the optical eye relief from the centre of the eye lens, however this lens may be concave and/or deep set in the housing reducing the effective eye relief.  Now your eye or more precisely your iris does not need to be at this point, but instead can be further back provided the iris (which when dark adapted has an opening of perhaps 5mm to 7mm in diameter) does not obstruct too much of the of the bundles of light rays, which is the cause of kidney beaning.  In practice your iris can be beyond the eye relief, particularly with a narrow apparent field of view or at high magnification (when the exit pupil is small). Further, if you are short sighted then your glasses will act as a mild barlow extending eye relief slight and the opposite for long sight.  Finally, some have thin glasses close to the eyes and others may have thicker glasses with deep set eyes.

While 15mm (or some would say 20mm) eye relief is good for glasses it is at best a starting point and you need to try for yourself.  I have been surprised at what works for me and what does not.  I am very short sighted (-11 dioptres) with close fitting glasses.   Some of my findings follow.

TMB type Planetaries: fine

Dual ED (Paradigm, Explorer): tight

Vixen NPL, 20mm (guard down) and 30mm (guard up): fine

Antares Orthos (similar to BGO), 9mm, 12.5mm: fine; 6mm: very tight

Vixen NVL, too tight with guard up, too long with it down...

Pentax XL, 8.5mm: tight

Baader Hyperion: fine

Baader Hyperion Aspheric 36mm: fine

Explore Scientific 68* with eye cup down, 24mm: fine; 16mm very tight

Explore Scientific 82* with eye cup down, 14mm: unusably tight; 8.8mm, 11mm: fine; 6.7mm: tight; 4.7mm: very tight

I hope this is useful...

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Just so as you know when i use the nikon i wear an old pair of ultra thin lens specs in a fine qire type frame that fits very tight to the face and this makes it easy to use. 

However i have no idea what someone without glasses sees when they use the ep without moving thier head to get a comparison.  Next time out i will do just this to see how much i am missing out on if indeed anything at all. 

If resilts suggest little or no loss then i believe you may be onto a winner Michael. ?

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I have been using Pentax XLs for almost 20 years to good effect with glasses.  The XWs are slightly more difficult to use thanks to their eye lens being recessed about 3mm.  The Delos don't have this issue and are also as easy to use as the XLs.  The 12mm and 17mm Nagler T4s are a bit difficult to hold the view after mashing your glasses into them.  The 27mm Panoptic is similar, plus it will scratch up your glasses if you try mashing them into the eyecup.  The original 30mm ES82 with the removable mushroom eyecup is just useable with eyeglasses.  The 40mm Meade 5000 SWA is a dream to use with glasses once the onion eyecup is removed.  The 22mm Astro-Tech AF70 is easy to use with glasses once you unscrew and remove the eyecup, plus it is nearly sharp to the edge.  The 17mm and 13mm versions are equally easy to use, but have increasing amounts of lateral color and astigmatism toward the edge.  I also like the Celestron zoom eyepiece for Regal M2 once the eyecup is unscrewed and removed.  The original Vixen LV line is super easy to use with glasses, and sharp, but only yield a 50 degree AFOV from 9mm and up.  Below that, only 45 degrees.  I'd say your start with a Delos is a good one, but you'll want something producing around 75X to 100X as well.  That would be something in the 12m to 16mm range.  The 12mm Delos should be parfocal with your 8mm, so it would seem the logical choice.  I love my 10mm Delos.  Sharp and flat field, super dark background.

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