What makes an eye piece great?

[manny]

I ask this because I currently own these eye pieces
T.V. 8mm plossl
T.V. 15 mm plossl
Orion Stratus. 5mm,17mm,21mm
Meade qx 26mm
A few days ago I had the opportunity to observe the Orion Nebula & Jupiter using a friends 21mm ethos in a 12" Lightbridge on Orion Nebula and 8mm Ethos on Jupiter the views were great but I didn't get that wow factor actually on Jupiter the 8mm plossl gave me the better view and on Orion Nebula I was hard pressed deciding which one gave the most pleasing visual, Ethos or Stratus as there is a significant price difference I would have assumed the Ethos would blow the Stratus out of the ballpark the fact that it did not surprised me. So my scope has a f5 focal ratio would that have any significance on the Ethos' performance? as my friend uses a Meade LX 90 10" with a focal length of f 10 he too was astounded by the Stratus . So what criteria comes into play when we buy eye pieces?. I am short sighted so don't need glasses at the eye piece .So do we really have to spend big bucks for little improvement? what do you think?

Manny

[Allan]

What makes an eye piece great? Green writing around the eyepiece of course.

Just kidding.

Wide field, multi element eyepieces like Ethos aren't the best for planetary viewing. They are very good, but simpler 3 and 4 element eyepieces are favoured for dedicated planet stuff. And the TV Plossls are often referred to as the best eyepiece for observing Jupiter, because it's warm tone brings out surface details the best.

Personally, I think the Ethos is one of the best DSO eyepieces. They do take a little practice to figure out the best way to see the whole field of view. But it's worth the effort for the view you will get out of them.

Ethos are very well corrected and handle short f-ratio scopes ok.

[AG Hybrid (Adrian)]

Originally Posted by Allan

What makes an eye piece great? Green writing around the eyepiece of course.

You know... I was going to say this too.

[David Niven (David Niven)]

What make a great eyepiece?
Great price, of course ...as it is good for your ego due to the fact that, not many can afford it and you are in an exclusive class!
I am kidding ....sorry.
Honestly, you don't need hundreds of dollar ep, to enjoy the hobby.
In my early days, I started out with the TMB planetary 6mm which cost less than a hundred dollars and they are good.
Since then, I have added a couple of ES and s Pentax XF but nothing more fanciful north of $200.
Pick your ep carefully. 3 good ep is sufficient but certainly not more than 5 IMHO.
Do not end up being an ep collector rather than a user.

[Wavytone]

My 2 cents...

1. Great image quality in the scopes you use,
2. Comfortable for long periods of use,
3. Minimise the fiddling when changing from one eyepiece to another. That means a set of par focal eyepieces (refocusing is minimised), all the same barrel size (no adapter to swap) and roughly similar weight to avoid rebalancing the scope.
4. wider field is nice but should not be the most important factor in choosing eyepieces.
5. Cost ... Set yourself a budget (upper limit). Below that I don't care about cost.

[MattT]

Think Wavy has summed it up perfectly
In my case White lettering ES 68º and Pentax XW's with an f12 refractor….perfecto!
Matt

[Don Pensack]

Well, reading eyepiece forums might lead you to believe there are vast differences in the quality of eyepieces in the center 25% of the field, and there just aren't.
I've owned over 300 different eyepieces through the years, and when the seeing was superb I was wowed by all but 3 of them and one of them was defective.
The point is, you won't see HUGE differences in the center of any functioning eyepiece in your scope (unless the eyepiece has poor color correction, like a Huygens).
At f/5, the differences that matter are:
--astigmatism in the outer 25% of the field
--field curvature that makes stars slightly out of focus at the edge when the center is focused.
--scattered light from bright objects outside the field of view caused by inadequate suppression of internal reflections
--differences in rectilinear and angular magnification distortions in the outer areas of the field
--light drop off at the edge (vignetting)
--overall shrpness of the star images (mostly in outer field)
--rendition of color, like a better revelation of red tints in nebulae, or a whiter image when the viewed object is white (e.g. Saturn's rings, certain lunar features)
--superior control of exit pupil aberrations
I could go on and on. The gist of it is that nearly all the differences show up in the outer 50% of the field, and not in the center 50%.
And last, an f/5 scope that is not using a coma corrector will also reveal substantial coma in the outer field. That's the optics, not the eyepiece, but it will be seen more easily in wider apparent fields.
So do you need the more expensive eyepieces to have a good time observing? No, of course not.
But for the outer 50% of the field? We have a saying: Wide field, inexpensive, well-corrected: Pick any two.

[Wavytone]

Don I disagree. You imply most eyepieces - even the cheap ones are reasonably good. This is simply not true - there are bloody awful ones out there which belong firmly in the trash. While it is true that something as deceptively simple as a plossl works well in a Newtonian, or a Ramsden or Huygens in a refractor - these are invariably a good match for the scope they are used with. And a little optical analysis will show why.

Your asertion assumes all telescopes are more or less equally good - and give flat fields free of the monochromatic aberrations. That simply isn't the case - compare the field curvature of newtonians to that of refractors, as well as SCT and maks.

It's already obvious that each type of eyepiece will suit some scopes, but not others, due to field curvature alone. Certainly not all. Several members in this forum have done side by side comparisons to establish this. To the extent a fair amount of buying and selling has occurred as observers try to optimise their eyepieces to match their scopes, once they know what works well - and what doesn't.

Anyone who made the mistake of buying Koenig eyepieces will understand this, most ended up fairly rapidly in the trash IMHO.

There are other issues with specific eyepieces, too. Some Naglers are notorious for "kidneybean", due to excessive amounts of spherical aberration in the eyepiece.

It's also evident that the designs of virtually all premium eyepieces since 2000 contain some amount of field curvature and negative coma, to suit fast newtonians while remaining tolerable in SCT's and maks.

IMHO it's high time eyepiece manufacturers started to state which type of scope their eyepieces are optimised for, instead of keeping this a dirty secrecy and leaving observers the task of finding out by trial and error.

If this happened buyers might actually be able to make rational choices - instead of finding out by trial and error.

I have been tempted to set up an optical bench to test eyepieces and publish the results (I have a physics degree and a long background in ATM and have designed optics before). I'm also quite sure some manufacturers will have a heart attack at the thought of this, and would dearly love to kill that information off.

[manny]

Thanks Don & Wavytone for your replies.

Wavytone I agree manufacturers should state what particular scope their
eyepieces are designed for ,and as you mentioned trial and error is just not good enough. How difficult would it be to say ideal for f/5 Newtonians etc,


Manny

[Harb]

So is there a data base somewhere that users have put together compiling which eyepieces work best withy which scopes ?

[Don Pensack]

Originally Posted by Wavytone

Don I disagree. You imply most eyepieces - even the cheap ones are reasonably good. This is simply not true - there are bloody awful ones out there which belong firmly in the trash.

Well, most people don't own Huygens and Ramsden eyepieces, and you will note that i mention the center 50% of the field in my post. The differences are largely in the outer field.

While it is true that something as deceptively simple as a plossl works well in a Newtonian, or a Ramsden or Huygens in a refractor - these are invariably a good match for the scope they are used with. And a little optical analysis will show why.

Your asertion assumes all telescopes are more or less equally good - and give flat fields free of the monochromatic aberrations. That simply isn't the case - compare the field curvature of newtonians to that of refractors, as well as SCT and maks.

And you're right. Different telescopes produce different aberrations. Eyepieces, in general, have far fewer serious aberrations to put up with. I certainly would not state there are not differences. And those differences may justify spending more for eyepieces. And certainly there are interactions between scopes and eyepieces. But just about any modern eyepiece will do OK in the center of the field with just about any modern telescope.

It's already obvious that each type of eyepiece will suit some scopes, but not others, due to field curvature alone. Certainly not all. Several members in this forum have done side by side comparisons to establish this. To the extent a fair amount of buying and selling has occurred as observers try to optimise their eyepieces to match their scopes, once they know what works well - and what doesn't.

Again, you're talking about the outer edges of the field.

Anyone who made the mistake of buying Koenig eyepieces will understand this, most ended up fairly rapidly in the trash IMHO.

Konig designed 28 different eyepieces in his time at Zeiss, and the modern Brandon and Clave Plossls were probably his design--possibly the 5 element "Astroplanokular", too--so you are generalizing. And some Konig eyepieces work just fine in some scopes. Had the commercially-produced ones (I'm thinking University Optics here) been confined to 50 degrees, they would have given Plossls a run for the money in terms of longevity in the market.

There are other issues with specific eyepieces, too. Some Naglers are notorious for "kidneybean", due to excessive amounts of spherical aberration in the eyepiece.

Only the first generation of Naglers had this "spherical aberration of the exit pupil" and once it was identified was eliminated from all future Naglers. The eyepiece itself did not have spherical aberration. And if you used them in scopes where the eyepieces didn't produce overly-large exit pupils, they worked fine. I owned them all and though you had to hold your head very steady to avoid the kidney bean type blackouts, it was possible to do so. And the fields were sharp very far out toward the edge.

It's also evident that the designs of virtually all premium eyepieces since 2000 contain some amount of field curvature and negative coma, to suit fast newtonians while remaining tolerable in SCT's and maks.

Completely false. I know many of the designers, and there are no commercial eyepieces currently produced that have inherent coma correction. It would then make no sense for TeleVue, Explore Scientifics, Baader, GSO, Keller and others to produce coma correctors were that the case. An eyepiece that doesn't have astigmatism or lateral color induced by the fast light cone of a short reflector works fine at longer focal ratios. It's not an either/or proposition. Earlier eyepieces weren't designed with such short Critical Focal Ratio figures because the scopes didn't exist. In this era of commercially available scopes down to f/3 an eyepiece designer worth his salt would have to pay attention to that.

IMHO it's high time eyepiece manufacturers started to state which type of scope their eyepieces are optimised for, instead of keeping this a dirty secrecy and leaving observers the task of finding out by trial and error.

I've advocated for years that all manufacturers should state the Critical F/Ratio of their eyepieces, but I understand why they don't. If an eyepiece wouldn't work well in your f/4 dob, you wouldn't buy it. The literally thousands of posts from people who state that a certain eyepiece doesn't work well in their scopes but they love the eyepieces anyway says that a lot of observers aren't very fussy, either.
However, that Critical F/Ratio figure is available on-line for most designs.
Here is one such place:
http://www.brayebrookobservatory.org...fEYEPIECES.pdf

If this happened buyers might actually be able to make rational choices - instead of finding out by trial and error.

Well, the issue is the continued production of eyepieces only suitable for long focal ratio telescopes in this era of short f/ratio telescopes. If you care about star images in the outer field, and you prefer wide fields, you will pay for those eyepieces. If you don't care about wide fields, inexpensive eyepieces will serve you fine down to whatever f/ratio your telescope turns out to be.
Of course, one could just avoid Huygens, Ramsden, Kellner, Erfle, Monocentric, and Abbe-orthoscopic eyepieces and you'd be far likely to have better results. Judging from how many laudatory posts I read for some of those designs, though, quite obviously many users don't really care about the quality of star images in the outer field.

I have been tempted to set up an optical bench to test eyepieces and publish the results (I have a physics degree and a long background in ATM and have designed optics before). I'm also quite sure some manufacturers will have a heart attack at the thought of this, and would dearly love to kill that information off.

You might try looking at the published reports on the Ciel et Espace website. Here are a couple examples:
http://www.cieletespace.fr/files/Ins...aires_10mm.pdf
and
http://www.cieletespace.fr/files/Ins..._oculaires.pdf
If your browser doesn't automatically translate and you don't read French, you can cut and paste sections of text into a translation site like Google Translate.
They test eyepieces down to f/3.5 and publish wavefront error and resolution figures for their test subjects.

[AG Hybrid (Adrian)]

What makes an eyepiece great? Majesty Factor. 'Nuff said.

[dannat (Daniel)]

Comfort...that when you use it you forget about it...

You can use it for long periods, little eye strain, no blackout/kidney beaming
Leave talk of edge correction to people who are never pleased no matter what they have in front of them...or the rich

[Wavytone]

Don,

I'll again call you disingenuous.

I am absolutely *sure* you know Plossls have negative coma and field curvature which just happens to match short focal-length newtonians.This is why such a simple eyepiece has survived so long, and continues today as a very good budget eyepiece among the users of short Newtonians.

I simply do not accept the makers of premium eyepieces - and I put Teleview, Explore, Pentax, Vixen and Nikon in this group - are not aware of the tradeoffs to be had by designing eyepieces to match about 50-60% of the field curvature and coma of the average light-bucket (a fast newtonian say 30cm f/4.5) on the basis that this will be equally a match in a smaller refractor (10-15cm f/7) or the average 20cm SCT.

Aberrations as seen by the observer are the sum of all the elements - scope + eyepiece - not eyepiece alone. I suggest you are well aware of Peztval's contribution in this area.

[Don Pensack]

Originally Posted by Wavytone

Don,

I'll again call you disingenuous.

I am absolutely *sure* you know Plossls have negative coma and field curvature which just happens to match short focal-length newtonians.This is why such a simple eyepiece has survived so long, and continues today as a very good budget eyepiece among the users of short Newtonians.

I simply do not accept the makers of premium eyepieces - and I put Teleview, Explore, Pentax, Vixen and Nikon in this group - are not aware of the tradeoffs to be had by designing eyepieces to match about 50-60% of the field curvature and coma of the average light-bucket (a fast newtonian say 30cm f/4.5) on the basis that this will be equally a match in a smaller refractor (10-15cm f/7) or the average 20cm SCT.

Aberrations as seen by the observer are the sum of all the elements - scope + eyepiece - not eyepiece alone. I suggest you are well aware of Peztval's contribution in this area.

Well, we may have to agree to disagree.
Plossls do NOT have negative coma and the field curvature that exists runs the wrong direction for newtonians (both positive). But typical dobsonians have such long focal lengths they essentially have no field curvature to speak of. Figure it out. In a 42mm field, your 30cm scope would have such a tiny amount of field curvature that designing an eyepiece to correct it would be very difficult. Flat fields make the most sense. And I have used far too many eyepieces (e.g.35 Panoptic, all 4 longer focal lengths of Pentax XWs, Nagler T4s, etc.) with field curvatures that should be the opposite direction to have any cancellation occur.
And I have certainly seen my fair share of coma in Plossls in short f/ratio dobs. All you have to do to test the hypothesis is to stick one in a Paracorr and watch the eyepiece get sharp to the edge. If they corrected coma, they would be worse in a Paracorr, not better.
A manufacturer would have to be an idiot to design an eyepiece that would only work in newtonians given that roughly 2/3 of the market is other kinds of scopes (SCTs, MCTs, Refractors, etc.). And so they don't.
Sometimes other corrections leave in some curvature, or astigmatism, in the attempt to create a flat Petzval surface.
The Plossl has survived as long as it has because the modern variants (Brandon, Clave, TeleVue, et.al.) were designed so that the oblique angles of f/4-f/5 scopes wouldn't induce extra astigmatism in the field.
Better correction is possible, though, and there are some eyepieces coming out now that are better corrected at such short f/ratios--even 25 degrees off axis.
The Plossl eyepiece pre-dates the popularity of short focal length newtonians. So does the Abbe orthoscopic. Yet both are popular for narrow field eyepieces in dobs and other scopes because they are fairly well corrected.
There have been eyepieces designed for dobs (the Praetoria design by Klee comes to mind, as well as his barlows), but they are the rare exception.
Look, I've seen the ray traces and spot diagrams for many of the modern eyepieces. I've seen the tests measuring astigmatism and wavefront error.
Have you?
I am NEVER disingenuous, and I resent your calling me that.
You know not whereof you speak.

[FlashDrive (Poppy)]

Originally Posted by dannat

Leave talk of edge correction to people who are never pleased no matter what they have in front of them...or the rich

...How true....How true ...!!

I like it....

ANYWAY.....for me it's....comfortable eye relief ....and good optics.

Flash......

[Tropo-Bob (Bob)]

Re Plossls, my experience has been that the longer the telescopes F ratio, then the better the image, so I respectfully disagree with the idea of negative coma.

However, I really dislike Possls below 15mm, as the eye relief is really too short because in part, I do not like my eyelashes touching and leaving marks on the lens.

Eyepieces that I favour generally have from 15mm to 20mm eye relief, at least a 60 degree field, do not weigh too much, and have a sharp image almost regardless of the F ratio.

Personally, I like the Radians (although the smaller focal lengths are a bit heavy), and I have a 13mm ethos (which is really uncomfortably heavy) which I also like.

Recently, I have taken some pleasure in trying to estimate the colour of the nova in Centaurus. I thought the radians gave a slighty false, warm colour, so out come a rarely used Meade 20mm SWA, which in my opinion is better colour corrected. So it can really be horses for courses.

At my age (58), I have become more fussy with eyepieces. I can remember being an enthusastic 13 year-old amatuer and both myself and a friend wondered why binoculars come with a fine focus for the second eye, as it always seemed in focus regardless of where we focused it. I wish my eye had retained that capacity to compensate, as getting that fine focus right is now very important requirement for me being able to see clearly. In a similiar vein, for general viewing, I used to greatly favour eyepieces that gave an exit pupil of about 5mm, now I prefer those with an exit pupil of about 3.5mm.

So it a nutshell, different eyepieces have come in and out of my favour depending on what I wish to use them for, and sadly, the state of my eyes, as I age.

I actually thought I had found the 'perfect' eyepiece when I brought a Unitron 25mm Kellner, some 44 years ago. I have found many perfect ones since, but I am still looking, as the improvements in my astronomical-lifetime have been absolutely amazing.

[WilliamPaolini]

Originally Posted by manny

So what criteria comes into play when we buy eye pieces?. ... .So do we really have to spend big bucks for little improvement? what do you think?

Manny,

Hello. This question is always an interesting one because I think the answer lies not where one expects. When talking an eyepiece I think most will think the list of criteria should be relative to the optical performance of the eyepiece. I think this is not the case. Sure it is a consideration, but by far not the entire story.

For me, I find what makes a great eyepiece is when all of its different attributes come togather in such a way that it meets or exceeds my personal expectations. For me, I generally look for a FOV that is sharp over 85%, so I'm not too concerned about that outer portion near the field stop since I am not a field stop observer Build quality and ergonomcs then come into play...I do not like overly large eyeieces and I like them to feel good when being handled. I am less concerned about eye relif and more concerned about eye positioning behavior...so how well is the exit pupil designed for my preferences. I don't like them to be too sensitive to eye placement...and further, the designer has a choice of where they form the image with the exit pupil...they can place the image formation near the cornea of the eye...or have it form in the center of the eye. In the case of the latter, you can then glance at the field stop in wide fields without the FOV going partially black. The XWs are like this...you can roll your eye around and the entire FOV stays brightly lit. Many other wide fields are not like this.

So it's lots of little things that define my personal preferences and optical quality is not the only one or the primary one. Case in point is I owned both a 12T4 Nagler and a 13mm Hyperion and kept them both for about half a year deciding which was best for me. The 12T4 put up a little better view, especially being sharper near the field stop (it was not sharp at the field stop), but to see the entire FOV I had to dip my eye very close to the eye lens. The Hyperion was more comfortable to view, and the FOV was almost as sharp in the off-axis as the 12T4, plus ergonomically its dual skirt design was much easier to use than the 12T4. In the end, I sold the 12T4 and kept the Hyperion.

So to make the determination of whether it is worth it to upgrade to another brand or line, I think it has less to do with the optical performance and more to do with is there some set of features in the new eyepiece that are accomplished much better in the new eyepiece. if so, then an upgrade is probably somethign that will satisfy you. For me now, I have the Pentax XWs as my wide fields. Some others out there have better off-axises, but none I have viewed through have better on-axises. The XWs have a superb on-axis being low in scatter and sharp and tone neutral and this all makes star fields for me to pop with a 3D-like view. While there are other eyepieces out there with more expansive AFOVs and maybe a better far off-axis in the longer focal lengths...this is not a big enough deal to spend more money. Now if someone could put the XW performance in the package of a Plossl, then that would turn my hear...and eye I'm sure

So in the end, I feel eyepieces are like gloves...you just gotta try them to see which fit you personally the best...and then they become the best, whether that is a Plossl or some uber wide field. And as long as you are not disatisfied with your eyepieces, then there is zero reason to replace them, even if they are Huygens!

-Bill

[bratislav (Bratislav)]

Originally Posted by Wavytone

I am absolutely *sure* you know Plossls have negative coma and field curvature which just happens to match short focal-length newtonians.This is why such a simple eyepiece has survived so long, and continues today as a very good budget eyepiece among the users of short Newtonians.

I simply do not accept the makers of premium eyepieces - and I put Teleview, Explore, Pentax, Vixen and Nikon in this group - are not aware of the tradeoffs to be had by designing eyepieces to match about 50-60% of the field curvature and coma of the average light-bucket (a fast newtonian say 30cm f/4.5) on the basis that this will be equally a match in a smaller refractor (10-15cm f/7) or the average 20cm SCT.

This is patently untrue. The only eyepiece with deliberately designed-in coma was now defunct Pretoria.
Televue, Pentax, Nikon etc will never design an eyepiece to match light-bucket (fast Newtonian) aberration pattern, primarily as their main telescope production are premium refractors. It wouldn't make sense for TV eyepiece to show coma and field curvature in one of their their ultra corrected, flat field refractors, would it?
You have also mixed things up; Newtonians have opposite field curvature to those of short refractors/SCTs. Say you design your premium eyepiece to match a ROC of a fast Newtonian, it would then be absolutely horrendeous in a SCT.
Not a smart market move, is it?

[Miaplacidus (Brian)]

It has Televue Panoptic 24 written on the side.