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2" eyepieces - how is bigger better? Or is it?

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#1 Jethro777

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Posted 07 December 2018 - 03:45 AM

I understand that a 2" focuser with a 2" eyepiece is optimal light. But, from a strictly visual observational point of view, what do you notice? Brighter detail?
Will a 2" 30mm eyepiece give you a wider fov than a 1.25" 30mm eyepiece?

#2 Jond105

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Posted 07 December 2018 - 03:49 AM

A 2" eyepiece with a 68 degree FOV will give you more than a 30mm plossl yes. Every eyepiece has a field stop. Every eyepiece is manufactured to a certain amount of FOV. Once the FOV cannot be reached in a 1.25", it then moves up to a 2". Some eyepieces all use a 2" barrel or 1.25 combined like Orion stratus'. I think mainly so you don't have to mess with adapters.

#3 sg6

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Posted 07 December 2018 - 04:43 AM

Basically 2" eyepieces are for lower magnification and so a wider view. So if that is paramount to you then you need to consider 2" eyepieces.

 

I have about 40 eyepieces, 1 is a 2" and I can honestly say I have never used it. I find I am quite happy with 1.25" eyepieces. Maybe I would like to drop a good 2" into the Megrez90 and view all of M31 in one go but that is about all I could think of. Presently I just use a 1.25" and a smaller 70mm scope.

 

A 2" eyepiece is big, go look at one first, they are not a little bigger they are 4x bigger. Owing to the additional glass and the aberrations from lens they tend to cost a fair bit more also.

 

The big disadvantage is they are for low power, people find a target then increase the magnification, and that magnification increase means 1.25" eyepieces. And the 2" to 1.25" swap is not eyepiece out-eyepiece in, there is the adaptor to take into account. And in the worst cases an extender for the eyepieces somewhere.

 

In a way rather like binoculars, 15x70's sound better, bigger etc but the vast majority of binoculars people use are 8x42's. That bird on a branch - wouldn't it look better in 15x70's then 8x42's ? So why are the smaller ones dominent?

 

A 2" eyepiece will be better for some uses, but I think the number of situations is more limited then expected, say 10% of the time, maybe less.


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#4 jallbery

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Posted 07 December 2018 - 05:01 AM

If an eyepiece design will fit without compromise in a 1.25" barrel, there is no optical advantage in putting it in a 2" format.   For 50-52-degree designs, the transition point happens around 32mm.   You can buy a 40mm 1.25" plossl, but it will show you the same field as a 32mm plossl, just with less magnification and a bigger exit pupil (a brighter view).  For 68-degree designs, the transition point is usually 24mm.  For 82-degree and wider AFOV designs, the transition is typically before it would be dictated by the field stop diameter due to the size and weight of these designs, but most 82-degree eyepiece's are in 1.25" format if they are 16mm or shorter.  For 100-degree designs,  the transition point is around 13mm.

 

 

As noted by Jond105, some eyepieces come with dual skirts that allow them to fit in either 1.25" or 2" diagonals.  Generally speaking, this is only for the convenience: a 17mm Hyperion (for example) won't perform any better in a 2" diagonal than it will in a 1.25", assuming both diagonals are of equal quality.


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#5 Jon Isaacs

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Posted 07 December 2018 - 05:58 AM

I understand that a 2" focuser with a 2" eyepiece is optimal light. But, from a strictly visual observational point of view, what do you notice? Brighter detail?
Will a 2" 30mm eyepiece give you a wider fov than a 1.25" 30mm eyepiece?

The field of view of an eyepiece is determined by the field stop, that's a ring at the focal plane that you see as the edge of the field. The larger the field stop, the larger part of the sky you can see. The maximum diameter of the field stop is determined by the barrel size, for 1.25 inch eyepieces, that's about 27 mm, for 2 inch eyepieces, about 46 mm.

To answer your question, a 30 mm 2 inch eyepiece has the potential to provide  a wider field of view than a 1,25 inch 30 mm and from a practical standpoint, nearly all of them do.

Unlike SG6, I have several 2 inch eyepieces and use them them frequently. The wider fields are an advantage but since they're generally longer focal lengths, they also provide brighter views. If one is organized swapping between 1.25 inch and 2 inch eyepieces only takes a few seconds extra and the views can make it worth the effort.

In general, I'm think one benefits from at least one low power, longer focal length 2 inch wide field eyepiece. Some objects are larger so depending on the scope, a 2 inch eyepiece may be necessary. The Pleiades, The Veil, the North. American nebulae require a 2 inch eyepiece in many scopes  to be seen in their entirety.  But with a 2 inch eyepiece, new vistas/views open. One is not necessarily just looking at a single object, multiple objects in one field, slowly scanning larger fields of nebulosity, large starfields, it another way of looking at the universe.

And too, for star hopping, the wide field provides two advantages. It's A bigger window so it's easier to put want object in the field of view. It is also easier to star hop in the main eyepiece , more stars, more room to work.

And of course, the views such eyepieces provide can be very special.

Jon


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#6 junomike

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Posted 07 December 2018 - 08:12 AM

For me It's all about the largest FOV possible (for DSO's). That's almost  always a +30mm Field Stop which requires a 2" eyepiece.


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#7 rogeriomagellan

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Posted 07 December 2018 - 08:23 AM

The field of view of an eyepiece is determined by the field stop, that's a ring at the focal plane that you see as the edge of the field. The larger the field stop, the larger part of the sky you can see. The maximum diameter of the field stop is determined by the barrel size, for 1.25 inch eyepieces, that's about 27 mm, for 2 inch eyepieces, about 46 mm.

To answer your question, a 30 mm 2 inch eyepiece has the potential to provide  a wider field of view than a 1,25 inch 30 mm and from a practical standpoint, nearly all of them do.

Unlike SG6, I have several 2 inch eyepieces and use them them frequently. The wider fields are an advantage but since they're generally longer focal lengths, they also provide brighter views. If one is organized swapping between 1.25 inch and 2 inch eyepieces only takes a few seconds extra and the views can make it worth the effort.

In general, I'm think one benefits from at least one low power, longer focal length 2 inch wide field eyepiece. Some objects are larger so depending on the scope, a 2 inch eyepiece may be necessary. The Pleiades, The Veil, the North. American nebulae require a 2 inch eyepiece in many scopes  to be seen in their entirety.  But with a 2 inch eyepiece, new vistas/views open. One is not necessarily just looking at a single object, multiple objects in one field, slowly scanning larger fields of nebulosity, large starfields, it another way of looking at the universe.

And too, for star hopping, the wide field provides two advantages. It's A bigger window so it's easier to put want object in the field of view. It is also easier to star hop in the main eyepiece , more stars, more room to work.

And of course, the views such eyepieces provide can be very special.

Jon

Jon,

 

Some high power eyepieces have be used in a 2" format like the Baader Morpheus series. One of the biggest advantages would drifting time. Would that be the only gain?

 

 http://www.eyepieces...e_p/1103090.htm

 

I know that the particular eyepiece in question is well-made but from your point of view, do you think that this is worth it only for the Moon and planetary work?



#8 25585

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Posted 07 December 2018 - 08:56 AM

Where 2 inches, either as an only option, or a skirt to a 1.25" stem, is when an eyepiece is top heavy and tall. A 2 inch diameter is stronger, dispersing weight better, and putting less strain from leverage on your focuser, especially if racked out &/or also burdened with other optics underneath.

 

Tele Vue refractors have always come with sturdy 2 inch focusers to cope with their heavy, quality TV optics. 



#9 jallbery

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Posted 07 December 2018 - 09:06 AM

Jon,

 

Some high power eyepieces have be used in a 2" format like the Baader Morpheus series. One of the biggest advantages would drifting time. Would that be the only gain?

 

 http://www.eyepieces...e_p/1103090.htm

 

I know this was directed at Jon, but I don't understand the premise of the question.

 

The 9mm Morpheus is a dual-skirted eyepiece.  It does not have to be used as a 2" eyepiece. I suppose in a scope with limited focuser travel (like many Newts), it may only achieve focus as a 2"  (or alternatively, only as a 1.25", unless you use an extension tube).  But as long as you can achieve focus either way, I don't know why it would have to be used as a 2-incher.

 

The 9mm 76-degree 1.25"/2" Morpheus eyepiece isn't going to have any drift time advantage over the 1.25"-only  82-degree 9mm TeleVue Nagler or 8.8mm ES82.


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#10 Lt 26

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Posted 07 December 2018 - 09:13 AM

They make nice counter weights for front heavy short triplets. Anything over 1/2 pound goes in 2" adapter. These 1 pound 1.25" eyepieces don't make much sense to me.

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#11 jallbery

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Posted 07 December 2018 - 09:58 AM

I understand that a 2" focuser with a 2" eyepiece is optimal light. But, from a strictly visual observational point of view, what do you notice? Brighter detail?
Will a 2" 30mm eyepiece give you a wider fov than a 1.25" 30mm eyepiece?

Here's another way of looking at things...

 

The Vixen 30mm NPL is a very good 50-degree 1.25" eyepiece.  It costs about a $60.   In an 8" F/10 SCT with a 2" diagonal, it will give you a true field of view of about 0.74 degrees at 70X with a 3mm exit pupil.

 

The 30mm Explore Scientific 82 is a very good 82-degree 2" eyepiece.   It costs  $300.   In that same scope, it will give you a true field of 1.2 degrees at 70X with a 3mm exit pupil.

 

Both eyepieces offer the same brightness, and the same magnification.   The 30mm ES82 gives you a substantially wider field-- 1.6X wider, and almost 2.5X the area.   

 

Or I suppose instead of the Vixen 30mm, we could compare the Explore Scientific 30mm 52-degree, which would provide similar view, but is argon purged, etc. like the ES82, and costs $99.

 

That 1.6X wider view comes at a substantial expense. 

 

Now, in an SCT, there other ways of getting a 1.2-degree field.   You could buy a 55mm (or 56mm) 2" plossl.  Now you can have your 1.2-degree true field of view, but now the magnification will be about 38X.   Your exit pupil will be 5.5mm.   So you get less magnification, but a brighter view.  And a Meade 56mm 2" plossl is a decent eyepiece and costs about $80.     So you get the same true field, but at lower magnification.  But things are brighter.   And it costs less.   A 55mm Tele Vue Plossl-- as good as any max field 2" plossl you can find, costs about $240.   In contrast, the 31mm 82-degree Nagler costs over $650.

 

Or on an SCT, you can purchase the F/6.3 Reducer/Corrector for $130 and get a 1.2-degree field with that $60 plossl (or even a $35 one).

 

But a 30-31mm 82 degree eyepiece gives you (approximately) the same field you get with that big 2" 55-56mm plossl, but with the magnification and detail you get with a 30-32mm Plossl.   Many people find this wider apparent field at higher magnification to be more immersive and majestic. 

 

Different scopes have different requirements, though.   A 55-56mm Plossl is not a viable choice for an F/5 (or even faster) Dobsonian.  The human eye cannot accommodate the 11mm exit pupil (a 7mm is about as big as many people can go), so the effect is to stop down the scope, which on an obstructed telescope will make the shadow of the secondary hard to ignore, in addition to losing resolution and brightness.   Fast scopes require wider AFOV 2" eyepieces to maximize their fields of view.  So that $300 ES82, or the $650 Nagler will be required.  A relatively lomg, wide AFOV eyepiece that can handle fast focal ratios is big and heavy and expensive.

 

So the 2" format doesn't just allow you to wider apparent views, it allows you have longer focal lengths in more moderate fields of view.  A 2" 55-56mm plossl may be expensive compared to your basic $35 1.25" plossl, but its an absolute bargain compared to wide and ultrawide designs that will provide a similar true field.   But such an eyepiece is only viable for telescopes with slower focal ratios.


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#12 dan_h

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Posted 07 December 2018 - 02:21 PM

For me, two inch versus 1.25", isn't about what the differences in the eyepieces are. It is more about what the target is and what scope is being used. These two factors alone determine what size the primary image will be and that's what determines the needed eyepiece.  Image size = tangent of the taget size X focal length of the scope. 

 

For example, consider that a nicely framed image of the double cluster, (about 2 degrees), is just about 0.035 X focal length of the scope.  In a 1000mm refractor, this is about 35mm and it simply doesn't fit in a 1.25" eyepiece.  You can either use a two inch eyepiece that will field 35mm, or use a shorter focal length scope to get a smaller image to fit in a 1.25" eyepiece. (Alternatively, you can forget that target and look at something smaller.)

 

If you are strictly a planetary observer, you can probably get by with 1.25" eyepieces and never have to deal with the added weight, expense, and adapters involved with using two inch eyepieces.  But if you want to see all of the Pleiades nicely framed and you are using a scope 1000mm or longer, you need a two inch eyepiece. 

 

It's all about the target and the scope in use.  Brightness, field of view, drift time, balance, and expense are secondary considerations. 

 

dan


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#13 Spartinix

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Posted 07 December 2018 - 03:37 PM

If you want the maximum available true field you can not skip 2" eyepieces with as big as an apparent FOV possible that still provides enough eye relief your eyes (wearing glasses or not) require.

For now, the ES 92 degree series provide the biggest AFoV combined with the most eye relief (for observers who use glasses for observing), that I know of.


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#14 MitchAlsup

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Posted 07 December 2018 - 03:47 PM

For me the issue is not 2" versus 1.25".

For me I convert all my 1.25" EPs to 2" and put parfocal rings on them.

If the Ep is too light, I will machine up a 1.25"-to-2" adapter out of naval bronze.

I like to keep the entire set close to the weight of 31NT5


Edited by MitchAlsup, 07 December 2018 - 03:48 PM.


#15 Barlowbill

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Posted 07 December 2018 - 08:05 PM

Simply stated, you should have at least one (1) 2" eyepiece.  That's why they make so many eyepieces!  I have three (3), but only use them occasionally.  A 42mm producing 28.4 X; a 32mm producing 34 X; a 28mm producing 42.8 X.  More toys!  It really is great to see more sky.  Slewing with a wider field of view is just fun.  Get one and enjoy it.


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#16 CrazyPanda

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Posted 07 December 2018 - 08:21 PM

Jon,

 

Some high power eyepieces have be used in a 2" format like the Baader Morpheus series. One of the biggest advantages would drifting time. Would that be the only gain?

 

 http://www.eyepieces...e_p/1103090.htm

 

I know that the particular eyepiece in question is well-made but from your point of view, do you think that this is worth it only for the Moon and planetary work?

That eyepiece you linked to doesn't have a 2" barrel to increase drift time, it has a 2" barrel as a convenience for astronomers who either want a more secure point of attachment, or don't want to swap a 1.25" adapter in and out of their focuser.

 

The bottom line is that that eyepiece, optically speaking, requires only a 1.25" barrel. 


Edited by CrazyPanda, 07 December 2018 - 08:49 PM.


#17 ShaulaB

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Posted 07 December 2018 - 08:36 PM

Brightness is a function of the diameter of the primary mirror or objective lens(es).

Good contrast between the dark sky and the object viewed is definitely a quality to consider when choosing an eyepiece of any barrel size. As I get older, I crave nice contrasty views.

When the object you are viewing fills the 2 inch eyepiece just right, it is a wonderful thing. An app like Sky Safari or Starry Night has features that let you input scope and eyepiece parameters, then shows you how an object would look with that combination. Play with the software to get some idea of what to expect.

#18 Jon Isaacs

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Posted 08 December 2018 - 12:46 AM

Brightness is a function of the diameter of the primary mirror or objective lens(es).

 

 

The brightness of a star depends on the aperture of the scope .

 

The brightness of an extended object (nebula/galaxy ) depends on the exit pupil. 

 

Jon


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#19 25585

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Posted 08 December 2018 - 02:22 AM

If you want the maximum available true field you can not skip 2" eyepieces with as big as an apparent FOV possible that still provides enough eye relief your eyes (wearing glasses or not) require.

For now, the ES 92 degree series provide the biggest AFoV combined with the most eye relief (for observers who use glasses for observing), that I know of.

ES92s are excellent, beating Tele Vue at their own game. Hoping for more next year, a low 20s would be cool as neither Nagler 4 or Ethos have the eye comfort ES92s give.



#20 jallbery

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Posted 08 December 2018 - 10:45 AM

For me, two inch versus 1.25", isn't about what the differences in the eyepieces are. It is more about what the target is and what scope is being used. These two factors alone determine what size the primary image will be and that's what determines the needed eyepiece.  Image size = tangent of the taget size X focal length of the scope. 

 

For example, consider that a nicely framed image of the double cluster, (about 2 degrees), is just about 0.035 X focal length of the scope.  In a 1000mm refractor, this is about 35mm and it simply doesn't fit in a 1.25" eyepiece.  You can either use a two inch eyepiece that will field 35mm, or use a shorter focal length scope to get a smaller image to fit in a 1.25" eyepiece. (Alternatively, you can forget that target and look at something smaller.)

 

If you are strictly a planetary observer, you can probably get by with 1.25" eyepieces and never have to deal with the added weight, expense, and adapters involved with using two inch eyepieces.  But if you want to see all of the Pleiades nicely framed and you are using a scope 1000mm or longer, you need a two inch eyepiece. 

 

It's all about the target and the scope in use.  Brightness, field of view, drift time, balance, and expense are secondary considerations. 

 

dan

>>Brightness, field of view, drift time, balance, and expense are secondary considerations.

 

I assume by "field of view" you were referring to "apparent field of view" since true field of view seems to be your primary driver.

 

In many ways I think of things similarly.  I want the right eyepiece to give me an aesthetically pleasing view of the target object.  And certainly the true field delivered with the scope in question is probably (for me) the most important factor-- at least for anything but planets or other (angularly) small objects, where magnification probably becomes the biggest driver.  At least when it comes to choosing what comes out of the eyepiece case and goes into the telescope.

 

But as to what goes into the case to begin with, a whole lot of factors go into that:

  • Viewing comfort--  if it's too much hassle to look through, I don't want it.  I like eye relief, and I don't like kidney beaning and black outs.
  • On the low-power side of things, I need eyepieces that will maximize the true field of view for each of my telescopes.  So I have a 31mm Celestron Axiom (82-degree), a 38mm SWA (70-degree),  and a 56mm plossl.  For my F/6.1 refractor, the 31mm 82 is the best pick as the plossl delivers too big an exit pupil and the SWA's edges get fairly messy.  My other scopes all come in at F/10-F/15, where any of the three could be viable.   I also have a 40mm plossl, 35mm Ultima, 32mm plossl, and 24mm ES68 to max out the field in 1.25" format. 
  • In the mid range, I have assorted eyepieces for views at 50-52, 68-70, and 82 degrees.   It allows me to get the field of view and exit pupil that works best of an object.   I'm not overly enamored with ultrawide views.   In the mid ranges, my 68-70-degree eyepieces get the most use, but sometimes more or less magnification works better.
  • On the high power end, I want options that allow me to go up to 50-60X per inch of aperture.   Here, I don't really care about AFOV, as I almost exclusively use tracking mounts.  Little planets look bigger to me in a smaller field.  At 12.5mm and under, I have an assortment of Vixen LV long-eye-relief eyepieces,  and Meade HD60s.   Plus a couple of nice orthos, even though I generally desire more eye relief.
  • And then there are the favorites-- eyepieces that just work for me.  For example, I love the Celestron 26mm Halloween eyepiece.   I think I feel about it the way some folks feel about the 28mm RKE.   It has a nice big eye lens and it just seems to get out of your way and show you the sky.  It's sharp, and easy to look through.   It's comfortable for me with or without glasses.   If I don't need a little more field, I'll pick it over the 24mm ES68.
  • And on all of the above, price is-- of course-- a practical concern.   That's why I have 31mm Axiom instead of a 31mm Nagler.   And a 24mm ES68 instead of a 24mmPan.   And a 38mm SWA instead of a 41mm Pan (or even a 40mm ES68).   And HD-60s instead of DeLites.  And Vixen LVs and and NLVs instead of Radians.  I'd like to have the more expensive options, but with mostly slower scopes, the cheaper alternatives work satisfactorily enough for my needs.

On the last point, I'm sure some folks are thinking, "you know, he could sell all that mid-range stuff and probably get enough money to buy a few really good eyepieces."   And that's probably true.  And I get the whole "a few really good eyepieces is better than a whole bunch of mediocre eyepieces argument," and I understand how with wider eyepieces, you could get buy with just a few really good eyepieces.   I'm fussy about how I like objects framed though.  And so I like to have choices.  Furthermore, many (of not most) 82+ degree eyepieces don't have enough eye relief for me to be comfortable, even with my glasses off.


Edited by jallbery, 08 December 2018 - 11:18 AM.


#21 CrazyPanda

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Posted 08 December 2018 - 01:25 PM

ES92s are excellent, beating Tele Vue at their own game. Hoping for more next year, a low 20s would be cool as neither Nagler 4 or Ethos have the eye comfort ES92s give.

A full line of ES92s with the same optical quality as the 17 (17 is my only frame of reference with this series), would really be a winner. Right now I get the impression that ES has a reputation of being a budget-conscience alternative to Tele Vue, but their 92 series stands completely on its own merits. The *only* limiting factor to that series, is the lack of a good spread of focal lengths. It makes me wonder how many people don't want to bother investing in the series because they want a homogenous kit of a good spread of focal lengths. 

 

A full line of 92s with that kind of eye relief and quality from 3mm to 17mm (maybe a 21 or 22 if they could find a market willing to tolerate a 3+ pound eyepiece), would be incredible. 



#22 Spartinix

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Posted 08 December 2018 - 02:42 PM

ES92s are excellent, beating Tele Vue at their own game. Hoping for more next year, a low 20s would be cool as neither Nagler 4 or Ethos have the eye comfort ES92s give.

I had these 92s' in mind for a long time. An Ethos 13 changed my mind. I realize now that I LOVE the field stop being way out. I believe the 92s' are more comfortable (and others like the Docter 84°, Pentax etc..), but I will probably buy more lower eye-relief 100° ep's before I try something else.



#23 25585

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Posted 08 December 2018 - 07:42 PM

I had these 92s' in mind for a long time. An Ethos 13 changed my mind. I realize now that I LOVE the field stop being way out. I believe the 92s' are more comfortable (and others like the Docter 84°, Pentax etc..), but I will probably buy more lower eye-relief 100° ep's before I try something else.

If you can manage with less go for it! My 92s were bought on the back of personal disillusion with all Naglers as to their being unsuitable for my eyesight, and little promise from any other make or type, bar the Orion LHD LER 80° range (I own the 14 and 20).

 

Those Orions are made in Taiwan. It was the, I presumed,  mainland Chinese made Baader Morpheus range, which showed me that good eyepiece optics were not just made in Japan, Taiwan and Europe. 



#24 Starman1

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Posted 10 December 2018 - 12:17 AM

Jon,

 

Some high power eyepieces have be used in a 2" format like the Baader Morpheus series. One of the biggest advantages would drifting time. Would that be the only gain?

 

 http://www.eyepieces...e_p/1103090.htm

 

I know that the particular eyepiece in question is well-made but from your point of view, do you think that this is worth it only for the Moon and planetary work?

The Morpheus eyepieces are all 1.25" eyepieces and are used that way, normally.

For convenience in some scopes, they have 2" machined surfaces on the outside of the upper barrel so they CAN be used as 2" eyepieces, but that 

doesn't change the fact they are 1.25" eyepieces.  All have field stop diameters that fit in 1.25" barrels.


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