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ES14 v.s. Ethos 13

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#26 Daniel Mounsey

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Posted 01 May 2009 - 06:25 PM

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#27 Jim Romanski

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Posted 01 May 2009 - 07:27 PM

With regard to field curvature, you don't mention what kind of scope the 80mm refractor is. I have come to be skeptical of field curvature claims unless I read that said eyepiece was tested in a flat field scope such as the NP101/NP127 or other scope with a field flatener.


What field curvature did I say I saw, please correct me if I am in error? I basically advocated what appeared to be a tad more rectilinear distortion in the 14ES and a bit more pincushion in the 13 Ethos. It doesn't mean that it's a fact as some observers claim they see aberrations others don't. Many observers claim that the Pentax 20XW has a lot of field curvature, yet I personally don't find it obtrusive at all in fact I see considerably more pincushion in my 22 Panoptic than there is, field curvature in a 20XW.

I think you're confusing field curvature which is a distortion in the vertical plane with rectilinear distortion of which pincushion is one type that are in the horizontal plane. You see field curvature when an eyepiece focuses in the middle but not on the edges. Then if you refocus the edges and the center is out of focus...that's what field curvature is. It means that the focus point is different in the center of the field vs. the edges.

I also wish you would spare us the discussion of your distaste for the barrel undercut. It's been done and over done here. All the Televue eyepieces have it so it's really not relevant to the comparison and I found the discussion distracting. I know many people don't like it but some of us in the minority think it's a great idea. In fact I would argue that it's more useful as an eyepiece safety feature than the additional 21% Nitrogen in the ES eyepiece. You just have to remember to loosen the thumbscrew more with compression rings to clear it.

You sound a bit upset. :) I'll try and take it easy on the barrels for you.

Thank you for your concern over how I feel but I was just trying to make a point that what most of us are interested to read about in this comparison is the optical differences. A passing reference about how you prefer the smooth barrel of the ES to the undercut of the TV would have been sufficient...in my opinion. I'll go easier on you next time with my critque. :ranting:
 

#28 Tom T

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Posted 01 May 2009 - 09:43 PM

I basically advocated what appeared to be a tad more rectilinear distortion in the 14ES and a bit more pincushion in the 13 Ethos.


Daniel,

Pincushion *is* a type of rectilinear distortion.

And in regards to your earlier quote of my statement - you are most certainly entitled to your opinion. However, optical definitions aren't really a matter of opinion.

T
 

#29 OuterSpaced

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Posted 02 May 2009 - 02:21 AM

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#30 Daniel Mounsey

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Posted 02 May 2009 - 03:58 AM


I basically advocated what appeared to be a tad more rectilinear distortion in the 14ES and a bit more pincushion in the 13 Ethos.


Daniel,

Pincushion *is* a type of rectilinear distortion.

And in regards to your earlier quote of my statement - you are most certainly entitled to your opinion. However, optical definitions aren't really a matter of opinion.

T

I realize this statement sounds like a contradiction. I was merely indicating that while viewing an object (a particular tree in fact) during the day near the edge of field in each eyepiece, that the 14ES appeared a tad less straight than the Ethos, but once again and as I stated in my review, it was very subtle. I simply related that to rectilinear distortion because the term is usually related to straight lines seen during the day while pincushion is something we relate to more often during the night when stars appear pinched along the center. Are they the same thing? I suppose, but they are still two different terms and if they ARE exactly the same thing, then why bother to give them two different terms? I applied them both.

Regardless and Ironically, the center of the field still seemed more pinched along its "center" more so in the 13 Ethos during the night while viewing the stars, while the 14mm ES appeared more uniform, flatter or corrected along most of the field of view and everyone agreed, myself included.

In your defense, perhaps that part of the review is a bit vague and should be more clearly stated, but remember that these eyepieces have huge fields of view and a lot can happen in that field. You can't just lay optical laws in stone and say that's exactly how it's going to appear at night. That wouldn't be open minded now would it? I gave the slight edge in light through-put and contrast to the Ethos.

In my opinion, it isn't wise to sell certainty with optical terms and definitions without "experience". It's better to remain open minded about what you appear to be seeing and try to express it constructively. Quite frankly, it's very disappointing listening to some of the comments in forums with those who spend most of their time just reading and chatting yet, don't even have an inkling of experience in the field to back their claims. They read books and all the sudden they're optical experts. I'll give you an example. These discussions about OK4 vs. FPL53. If a person thinks it's a major concern, it's clearly an indication that they don't have the experience to realize they're asking the wrong question about their concerns. The observers mind is polluted with confusion because things on paper are very misleadng and things DO NOT always behave as the papers claim and you of all people should know that Tom. This is why I tell many of my customers to STOP gargling the forums and get out in the field and get experience. That's why I hold my own star parties twice a month. I help beginners by allowing them to see through different telescopes in the field.

There's nothing wrong with people trying to read books and reviews but at least "apply it in the field" for crying out loud, there's a BIG difference. You and I have been members of CN since 2002, longer than everyone. I have over 3000 posts to my name. The purpose of the forums should be to offer constructive insight and meaningful forums. Sometimes I admit having some fun in the forums, but I try to keep my posts short and meaningful so there's less for people to gargle and Instead what I see happening in many cases, is the forums being used like Facebook or Myspace.

I'm shocked that Televue openly admitted the change in coatings. With regard to Televue saying they use the same newer coatings with all their eyepieces, your statement is very misleading and you're trying to discredit the comments in my review. First off, most of the Televue's in circulation DO NOT have the newer coatings and the reason I know that, is because Televue told me they were just starting to use the newer coatings during last years open house at OPT. If that's not the case, then you and I are getting conflicting stories from Televue. From what I was told, the green and red stickers on the plastic sleeves the eyepieces come wrapped in are simply to inform Televue which eyepieces have the newer vs. older coatings but that's been going on a while. I also know Televue is reading and following this forum very carefully.

Secondly, Televue has been around for over 30 years. I find it very unlikely that the majority of consumers who own Televue's all decided to gather up and throw their Televue's in the garbage and buy new ones within one year. What I sated in my review about the coatings was valid. The Ethos do have the latest, greatest coatings and most observers who compare them will see a difference. :troll:
 

#31 Tom T

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Posted 02 May 2009 - 05:31 AM


I basically advocated what appeared to be a tad more rectilinear distortion in the 14ES and a bit more pincushion in the 13 Ethos.


Daniel,

Pincushion *is* a type of rectilinear distortion.

And in regards to your earlier quote of my statement - you are most certainly entitled to your opinion. However, optical definitions aren't really a matter of opinion.

T


I realize this statement sounds like a contradiction. I was merely indicating that while viewing an object (a particular tree in fact) during the day near the edge of field in each eyepiece, that the 14ES appeared a tad less straight than the Ethos, but once again and as I stated in my review, it was very subtle. I simply related that to rectilinear distortion because the term is usually related to straight lines seen during the day while pincushion is something we relate to more often during the night when stars appear pinched along the center. Are they the same thing? I suppose, but they are still two different terms and if they ARE exactly the same thing, then why bother to give them two different terms? I applied them both.


Daniel,

We're still not communicating.

Your initial statement was not a contradiction, it simply does not make sense.

There are two types of distortion that we need to worry about for astronomical eyepieces. Angular Magnification Distortion and Rectilinear Distortion. Further rectilinear distortion can be classed as one of two types - Pincushion or Barrel.

Pincushion and Barrel are a subsets of RD, RD is the superset.

To use an analogy, in saying that the Ethos has more pincushion and the ES has more RD - well, it's like you're talking about two cars, and you say one car is a sedan, but the other car is more of a car. They are both cars, but sedan is the particular type.

that the 14ES appeared a tad less straight than the Ethos, but once again and as I stated in my review, it was very subtle.


I think this statement, however, is indeed a contradiction with what you previously wrote.

Regardless and Ironically, the center of the field still seemed more pinched along its "center" more so in the 13 Ethos during the night while viewing the stars, while the 14mm ES appeared more uniform, flatter or corrected along most of the field of view and everyone agreed, myself included.


Ok. But here again, we run into problems - what do you mean by flatter? It too has an optical definition. Do you mean in terms of Distortion (either AMD or RD) or Field Curvature? These are fundamentally different aberrations. Optically to describe it as a flat field specifically refers to a lack of field curvature. (IE - focus does not change across the field.) But your statement sounds like you're talking about distortion.

In your defense, perhaps that part of the review is a bit vague and should be more clearly stated, but remember that these eyepieces have huge fields of view and a lot can happen in that field. You can't just lay optical laws in stone and say that's exactly how it's going to appear at night.


In the case of distortion, yeah - I think you pretty much can. There are lots of other things that can be affected by implementation (scatter for instance), but distortion is a design characteristic.

That wouldn't be open minded now would it?


It's not a case of being open minded. It's a case of understanding what's going on and why. These are basic optical concepts with established definitions.

You rather dismissively state that book learning without experience is of limited value - and there's certainly truth to that - as far as it goes. But ideally, people develop BOTH their education and their experience. Understanding without seeing is one thing. Seeing without understanding is another. IMO, everyone, but especially people who attempt to educate others (especially where technical items are concerned) should have or consider it a must to develop a good balance of both.

It's an ongoing process. In education we use the phrase "Lifelong Learner".

I gave the slight edge in light through-put and contrast to the Ethos.

In my opinion, it isn't wise to sell certainty with optical terms and definitions without "experience". It's better to remain open minded about what you appear to be seeing and try to express it constructively. Quite frankly, it's very disappointing listening to some of the comments in forums with those who spend most of their time just reading and chatting yet, don't even have an inkling of experience in the field to back their claims. They read books and all the sudden they're optical experts. I'll give you an example. These discussions about OK4 vs. FPL53. If a person thinks it's a major concern, it's clearly an indication that they don't have the experience to realize they're asking the wrong question about their concerns.

The observers mind is polluted with confusion because things on paper are very misleadng and things DO NOT always behave as the papers claim and you of all people should know that Tom.


Daniel, there are at least two phases - design and implementation. Design absolutely goes by the book. It has to. People can't begin to design things if they didn't have some assurance they'd have a working product. To see what they may have overlooked, as well as what may be implementation issues (that may not have been considered) you go through the prototyping and production prototyping process. When you're looking at a piece of gear critically it's important to know what is design and what is implementation. For example, IIRC Tak states the TSA has a design strehl of .992. We both know that does not mean every TSA has a strehl of .992, rather just that's the maximum design value - real world values will be lower. This is where a sound knowledge of theory comes it. It allows you to interpret what you see and effectively communicate it to others.

FWIW, I look at the times I'm confused (and there have been lots over the years) as an opportunity to merge practice and theory. I know the chances I'd develop a new optical theory are vanishingly small, ergo when I see something in practice that apparently goes against the knowledge of theory I have, it's almost certainly because my knowledge is flawed. These are learning experiences, but you have to recognize them as such.

This is why I tell many of my customers to STOP gargling the forums and get out in the field and get experience. That's why I hold my own star parties twice a month. I help beginners by allowing them to see through different telescopes in the field.

There's nothing wrong with people trying to read books and reviews but at least "apply it in the field" for crying out loud, there's a BIG difference. You and I have been members of CN since 2002, longer than everyone. I have over 3000 posts to my name. The purpose of the forums should be to offer constructive insight and meaningful forums.


I completely agree that people need to see what they like for themselves, and I always emphasize that, but that's not the point here.

I'm shocked that Televue openly admitted the change in coatings. With regard to Televue saying they use the same newer coatings with all their eyepieces, your statement is very misleading and you're trying to discredit the comments in my review. First off, most of the Televue's in circulation DO NOT have the newer coatings and the reason I know that, is because Televue told me they were just starting to use the newer coatings during last years open house at OPT. If that's not the case, then you and I are getting conflicting stories from Televue. From what I was told, the green and red stickers on the plastic sleeves the eyepieces come wrapped in are simply to inform Televue which eyepieces have the newer vs. older coatings. I also know Televue is reading and following this forum very carefully.

Secondly, Televue has been around for over 30 years. I find it very unlikely that the majority of consumers who own Televue's all decided to gather up and throw their Televue's in the garbage and buy new ones within one year. What I sated in my review about the coatings was valid. The Ethos do have the latest, greatest coatings and most observers who compare them will see a difference. :troll:


Daniel, that's not what my earlier coating statement was about. The purpose of coating an optical surface in an eyepiece is (typically) to increase throughput. According to them, Tele Vue's coatings do not now, nor ever have, changed the tone from warm to cool. Yes, coatings have changed over the years. (In fact, Tele Vue told me they had changed coatings several years back, and just reconfirmed it for me.) And their coatings probably will continue to change as better ones come out. (I'd expect that from any manufacturer.) And yes, older eyepieces will have different coating - But again - that's not the point. The point was you specifically stated that their coatings were responsible for changing the hue from warm to a cooler tone. According to them that's incorrect. Period.

Look, we're going in circles here, so this is my last word on the subject.

As I mentioned above, I think it's very important to both see and understand if you're trying to educate others. If one does not, the educator may unintentionally do a disservice to both the learner and the field. Misconceptions, once formed, can be very difficult to overcome.

Learning is an ongoing process. You have a great love of astronomy, and for that I commend you.

Please consider the following: One does not have to present things technically, and many folks benefit from that immensely, but if someone is going to speak technically and in an authoritative voice about technical items, then they have a responsibility to understand and use the correct terms for what they are describing, as well an obligation to ensure that the information provided is as accurate as possible.

Thank you.

T
 

#32 rob cos.

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Posted 02 May 2009 - 06:34 AM

I can't help thinking that no matter how Daniel had described his experience(technical or subjective) with these two eyepieces...he was still going to experience passive/aggressive posts in defense of Televue. :lol:

Getting past the technical jargon, I understood perfectly what Daniel was trying to say without the further discussion of his use of technical jargon or mentioning of undercuts.

And i'll bet plenty others did too.
 

#33 EdZ

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Posted 02 May 2009 - 06:44 AM

Field curvature usually causes the issues discussed rather than pincushion and I added some clarification regarding my statement "per your comments", so there were less misunderstandings. The problem is that when I moved the eyepiece left and right to check for either aberration, there was unquestionably a tad more pincushion in the 13 Ethos and so it's difficult to say for sure what it could be.


Field Curvature causes stars to progressively grow in size, from center to edge, from a tiny pinpoint into larger out-of-focus blobs. Identifying Field Curvature and separating it from other aberrations is fairly easy, since it is the only aberration that can be focused out.

Degree of field curvature can actually be measured. Not exact, but surprisingly fairly accurate. Using a variety of double stars, for instance a 10" pair at 60% out, a 20" pair at 70% out and perhaps a 30-40" pair at 90% out, (might need 5" 10" and 20" pairs, but I'll continue with those in my example) note the degree of aberration by how large do the disks of the stars grow at that position. Then refocus and note how large they appear to be grown again.

An example: eye piece in use gives 50 power; double star pair observed is 20 arcseconds. Position of pair is 70% out from center.
When precisely focused at center of fov, 20" pair positioned at 70% out shows bloated images just touch each other. Therefore at 70% out, "total aberrations" are causing 50 x 20" = 1000 arcseconds apparent aberration. Now leave pair at same 70% position and refocus "on them". If total aberration removed from image of the pair is half of bloated distorted image, then curvature removed by refocusing on them was responsible for 50 x 10" = 500 arcseconds apparent aberration, and the remaining total aberration is due to some combination of astigmatism, coma and/or spherical aberration. Curvature has now been measured at that position. In the absence of a field flattener, it almost always increases further out from center.

Pincushion shows no error in the image. It simply moves the image in the fov, so is almost impossible to see at night, unless it is extremely strong. BTW, pincushion is not necessarily an undesirable aberration, since it may be designed into the eyepiece to eliminate astigmatism. Pincushion to a small degree can be advantageous for daytime viewing since it reduces the rolling-ball effect. However, in general, these would not be considered daytime eyepieces.

edz
 






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