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Go Back   IceInSpace > Equipment > Eyepieces, Barlows and Filters

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  #21  
Old 29-04-2012, 01:06 AM
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mental4astro (Alexander)
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Dear, oh Dear!

I've just come in from a very interesting couple of hours with my 17.5" f/4.5 dob. Ol' Wavytone was very generous today (Saturday), and lent me a couple of his most prized pocessions, two of his LVW's, the 13mm and the 8mm. I was hoping to be able to compare them to my problematic 13mm Hyperion, and gererally be prepared to have my socks blown off. What happened in the end I did not expect.

What spurred this lending of Wavy's LVW's was both THIS thread, and my poor experience of my recently acquired used 13mm Hyperion. This thread without saying is a gem. My Hyperion however was a disappointment. Using the same 17.5" scope, the stars in the Hyperion refused to come to a nice, crisp, sharp focus. Sure, if you concentrated on a single star the image became pin-point, but it didn't hold. There was some sort of mismatch happening between the optics and my eyes. The field curvature was appauling too! I have never seen such a "fishbowl" effect in any eyepiece. My observing companion that night, erick here on IIS, also saw this. Major disappointment.

When Wavy' dropped of the eyepieces, we examined both 13mms. We noticed that the field lens of the LVW was convex, but that of the Hyperion was concave. Odd since this field lens arrangement is supposed to be a barlow, and should be the same if the Hyperion is a copy of the LVW.

I should note here before continuing that the bottom 1.25" section of all Hyperion EPs unwinds from the two inch barrel fitting. This is part of the modular construction of these EPs that allows for different extension rings to be used, there by allowing one EP to become of two, three or maybe even four different focal lengths. The 24mm (of which I also have one) the 1.25" barrel has no lens in it, therefore is an empty shell with a thread for filters.

My test DSO was Eta Carina. The Hyperion was terrible, as the first time I used it. The LVW was in a league of its own here. The added 3 degrees FOV of the Hyperion only provided a slightly larger AFOV, but the field stop was soft, while that in the LVW was a nice sharp edge.

Then, a fit of maddness overtook me. I swapped the 1.25" barlowed barrel of the 13mm Hyperion for the empty barrel of the 24mm Hyperion, AND to it added the barlow lens element of my $30 1.25" GSO 2X barlow. Man-oh-man! What a difference! All of a sudden, the "modified" 13mm Hyperion had found its Mojo. The bugger focused as sharp as the LVW. The field curvature was gone. The field stop was still soft, but not really of consequence, as the extra 3deg of FOV remained the same.

HOWEVER, the real difference came when I nit-picked the faint stars around in Eta Carina. Switching between modified Hyperion and LVW constantly, I was actually seeing more stars in the modded Hyperion that the LVW. A faint cluster of stars immediately beside the star Eta Carina in the LVW required averted vision to JUST see them. With the modified Hyperion, I could see these same stars directly! and them even more stars with averted vision!

Holy Crap!

Contrast wise I could not really notice any difference. Probably due to the heavy light pollution I was viewing from. But, I cannot get away from the fact that I could see more in the modified Hyperion that I could in the LVW! I was considering rolling my 13mm under a fast moving truck earlier today. I'm keeping her now! "Frankenstiened" and all.

I then moved onto the 8mm LVW. As Eta Carina had now moved into a more light polluted section of my sky, I the test DSO became the open cluster in Scorpio NGC 6231. My comparison eyepiece was my $50 9mm TMB Planetary Type II. This TMB eyepiece only has a 60degree FOV, compared to the 65degrees of the LVW. I was in for another surprise.

This modest TMB eyepiece showed better contrast than the LVW. At this magnification, approx. 200X, the background sky in the TMB was a little blacker than in the LVW. Really small, but noticeable. The same thing also happened with this TMB, where I was able to see more stars through it than in the LVW. It also focused sharper. While the FOV of the TMB was smaller, the AFOV was larger than that of the LVW, maybe 4" or 5" (minutes of arc that is).

All of a sudden, I am at a bit of a loss at what has happened tonight! I had expected to have my eyeballs assulted by the quality of the LVW, but they have been out done by a modified Hyperion, and a $50 TMB. I am guessing that the edge that the TMB also has is the bugger all glass it contains compared to the LVW. Still, I would not have imagined such a significant difference.

I have now reconsidered my eyepiece collection from what I had been thinking only upto four hours ago. Sorry all of you LVW affeccionados - you have lost me. Coming to this shoot-out tonight, I had been gunning for the LVW's. In the end I've got new champions, and they were in my eyepiece collection all this time!

Mental.
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  #22  
Old 29-04-2012, 03:37 AM
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Looks like you had a defective LVW because there is no way that any Hyperions or TMB planetaries would be any better than those eyepieces. I have tested an 8mm LVW and stars were all pinpoints from the center right out to the edges in my 10" f/4.72 reflector. I am talking nice tiny points of light here. I also put an LVW up against a barlowed 13mm Hyperion and the LVW bested it.

BTW, The field curvature is not coming from your eyepiece, it is coming from your mirror as I see it is @ f/4.5. Another thing, the field lenses of both the hyperion and the LVW do not a have a "barlow",they have a "smythe" lens.

Cheers,
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  #23  
Old 29-04-2012, 07:39 AM
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mental4astro (Alexander)
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Hi Markus,

First, I can't make an appology for what I saw down the eyepiece. I came to this evenings session completly with an open mind. No prejudice towards my gear, actually I favoured the LVW's. I very much looked forward to using these LVW's, particularly after reading your comments and Wavy's.

Symthe lens or barlow, I used the term as a description only by the way this lens has been described in many other threads I've read. Doesn't change things though. The only true "barlow" then is the one I stuck in the end of my Hyperion.

No, niether of these LVW's are defective. They are both superb eyepieces.

Field curvature comeing from the mirror. Could be. My definitions on optics is limited, so I apologise if I used the incorrect term here. "Fishbowl" effect then. The image displayed a distinct deformation as the scope was moved across the field, like that seen in a big, fat magnifying glass. I can only guess that there is some miss-match of "smythe" lens with my 13mm Hyperion. I have read only good reports from other 13mm Hyperion users, so I'm at a loss to know what happened there.

Come to think of it, yes, the field was tighter across a wider stretch of the FOV of the LVW, but the FOV distortion in the Hyperion only occured in that area that extends beyond the field stop of the LVW. Over the same FOV area, nope, I can't say I noticed any real difference.

Like I said, I came to this evening's comparison session expecting fantastic things from the LVW's. I wasn't disappointed. Fact remains that my modified Hyperion and my humble TMB out performed the LVWs. I saw more stars in them. Isn't that what it's all about? Even if at the extremes the FOV the stars didn't remain pin point, any softening in the Hyperion happened beyond the field stop of the LVW. And, it is not really an area that is used very much when observing. When the object gets so close the extreme edge, you will always move the scope to centralise the object in the FOV anyway. So, for me, this is good enough.

I have no bone to pick with anyone here. I could not be more objective in coming to an observing session. I would not write about what I did not see, especially as I have been seriously considering purchasing some LVWs from what had be written here by yourself and Wavytone - two very learned fellows! I've known Wavy for quite some time too. I consider my purchases very, very carefully, researching as much as possilbe. In the end I saw what I saw. Simple as that. I saw more stars.
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  #24  
Old 29-04-2012, 07:57 AM
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Hi Alexander!

Well, when you see something, that's the result! The link I posted earlier of the LVW's was not done by me, it was done by another astronomer, and I thought I would pass that info along.

From what I have saw in the LVW's, the views of stars were pinpoints right out to the edges with superior transmission in my 10" f/4.72 when I did own the 8mm Orion LVW and also tried a 22mm and 17mm LVW.

All three of them showed perfectly tight stars with excellent transmission, albeit a bit of lateral color. I had a 13mm Hyperion and an 8mm Hyperion and the edges showed some edge aberrations. The 13mm has some field curvature, which obviously comes from the mirror and maybe a bit from the eyepiece as well.....not 100% positive on that one.

If you see field curvature in an eyepiece, I believe it is always coming from the mirror no matter what eyepiece you use, ( I think?), but some eyepieces will show this more than others. If you see astigmatism in an eyepiece, it is the eyepiece at fault. I believe the "fishbowl effect" comes from rectilinear distortion.

Quote:
Even if at the extremes the FOV the stars didn't remain pin point, any softening in the Hyperion happened beyond the field stop of the LVW.
The LVW's and Hyperions almost have the same apparent field of view.

LVW's = 65
Hyperions = 68

As to your post: If it makes you happy to see what you saw, that is the bottom line and that is all that matters! if I or someone else sees things differently, it really doesn't matter! I wish you well, and hope you had a great observing session! Having a 17.5" f/4.5 is a great light bucket to have and I would hand over ALL of my eyepieces and keep just ONE just to own one of those size telescopes!

You sure do have a nice size scope there good sir!

Have yourself a great weekend and may you enjoy thousands more nights looking through that incredible light bucket!

Cheers,
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  #25  
Old 29-04-2012, 10:02 AM
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Hi Mental4Astro

Not to malign the TMBs & 13mm Hyperions (I have the latter too) nor act the champion of the Vixens but it might be worthwhile doing a comparison and thus test where relative parity exists in the designs.

In terms of the LVW you are comparing a widefield 8 element design against a smaller EP in the TMB. It might be worthwhile doing a comparison of the TMB against a LV or their contempoary incarnation the NLV.

With respect to the LVW's physically the Hyperions, LVWs, Stratus and Saxon widefields all look incredibly similar once you look past the different brand labels/paintwork. I have never looked through a LVW (only physically at them in stores) so I can't comment on their optics but what I like about Hyperions are their modular design and use of the FTR rings.

In my humble opinion and experience the few times you can most often discern some sort of consistently tangible yet significant difference occurs when the atmosphere conditions are really optimal. It is in those odd excellent times that my money bags colleague with his $1000 ZAO-II takes me to the cleaners (with my more modest EP collection) and I can really see differences when we try his EP's on different scopes while trying to keep everything to some degree of parity.

I think for $60 the TMBs are great and for $80-$120 a LV (2nd hand) is great too. However, when I start approaching anything over $300 I start thinking about light green painted letters or Pentax. When money is not an issue - well....... take your pick of the superleagues - I wonder how the new Takahashi widefields fair each at roughly $1000 -OUCH!! - My wallet is already trembling at the thought
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  #26  
Old 29-04-2012, 10:06 AM
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Alexander wrote:
Fact remains that my modified Hyperion and my humble TMB out performed the LVWs. I saw more stars in them. Isn't that what it's all about?

bad galaxy man writes:
Have you seen my post in this thread, comparing a 22mm LWW with a 20mm type II nagler (which is probably an unfair comparison (!!), as this Nagler is one of the very best designs in Nagler's "super premium" line of eyepieces).
The stars seen in the Nagler were noticeably brighter, and I had a fainter magnitude limit with the Nagler.

My impression of the LVW was that the actual light transmission of the LVW eyepiece was noticeably worse than the light transmission of the Nagler, leading to fainter images.

Could it be that the difference between the LVW and the other eyepieces you compared it with is something to do with the relative light transmission of the eyepieces?
(there are definite variations in the coatings, between different eyepieces......I don't think all of the antireflection coatings applied to lens surfaces are equal in effectiveness)

Sometimes, the images are brighter in a simpler eyepiece simply because it has fewer air-glass surfaces to reflect and scatter light!!

The use of a barlow is also a major factor; the fact is that , despite the bad reputation of barlows in some quarters, the narrower light cone of a barlow - at greater effective focal length - often also reduces the aberrations in the star images provided by an eyepiece.
(In my view, the idea of the bad effects of a barlow on views through an eyepiece has become something of an urban myth; an often repeated statement that has become
so-called "truth" due to constant repetition)

Last edited by madbadgalaxyman; 29-04-2012 at 10:19 AM. Reason: more
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  #27  
Old 29-04-2012, 11:18 AM
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Quote:
Originally Posted by mental4astro View Post
"Fishbowl" effect then. The image displayed a distinct deformation as the scope was moved across the field, like that seen in a big, fat magnifying glass.
Alex, that's pincushion distortion. It is common in eyepieces incorporating the Smythe lens design; essentially it means magnification is not constant across the field and varies radially from the centre.

Hehe I'm not surprised at your other remarks especially transmission, I have noticed that before. You tried the LVW's before at Katoomba and decided they were not exceptional so it' not really news...

As Robert said, there is a huge tradeoff in how much glass and how many surfaces vs field of view, transmission, contrast and image quality. For this reason if you're really serious about smallest objects rather than wide fields the best choice is an eyepiece with only 2-4 elements and few glass/air surfaces. This is why designs such as super-monocentrics, RKE, Plossl, orthoscopic and even Kellner are still useful. I often wonder what could be done if some of these older designs were revamped to take advantage of modern glass types, in particular ED glass.

Choosing eyepieces is an area where there are too many conflicting variables, about which most of us have little or no real information to make a decision. That leaves 'trying before buying' or pot luck. You're fortunate to be able to try alternatives, which was something I couldn't do at the time I bought them (they were half the price of Naglers too).

Last edited by Wavytone; 29-04-2012 at 11:33 AM.
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  #28  
Old 29-04-2012, 04:57 PM
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Wavytone,

your comments about using only a 2-4 element eyepiece for certain applications are very very interesting and very worthwile;
though there are some experts who would regard these comments as being highly controversial or questionable.

This sort of argument lead to the idea of a "planetary eyepiece" designed, for instance, to maximize freedom from scattered light in the field that is caused by reflections from multiple air-glass surfaces. For instance, the planetary observers swear that a good orthoscopic eyepiece can give planetary views that are better than those provided by many of the more complex eyepieces.
(Planetary surfaces are a severe test for any combination of optical elements, as the slightest unwanted or excess light that is in the diffraction disk or in the field....can lead to a loss of low contrast detail)

I note, however, that maximizing the contrast between the object and the surrounding field, also can improve the observer's view of a deep sky object. On stellar and non-stellar deep sky objects, the particular Nagler eyepiece that I mentioned had considerably superior contrast to the LVW I tested, to such a large extent that the difference was blatantly obvious even after a few seconds viewing;
but exactly what combination of smaller star images and/or greater light transmission and/or a smaller amount of scattered light, was actually the cause of this noticeably better performance by the 20mm typeII Nagler..... I do not know.

cheers, bad galaxy man

Last edited by madbadgalaxyman; 29-04-2012 at 04:59 PM. Reason: typo
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  #29  
Old 29-04-2012, 10:24 PM
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Well... there is an interesting comparison - one which I hope Alex might read too. The first part is comparison of the TMB supermonocentric against other modern high-contrast eyepieces - by Gary Seronik and appeared originally in S&T.

OK, most of you will think it is OK to do this kind of comparison, and those of you using f/4 Dobs with a paracorr will be having warm fuzzy feelings.

But this is followed by a critique by Chris Lord (Brayebrook Observatory) as to what is wrong with the test - starting with why a fast Newtonian reflector is a lousy choice of telescope to do eyepiece comparisons:

http://www.brayebrookobservatory.org..._critique.html

But I think Chris Lord was also a little harsh - there are examples of eyepieces having been designed to match the aberrations of specific telescopes - starting with the (now rare) Pretoria eyepieces and RKE's. So in this respect if you have found an eyepiece that YOU like, on YOUR scope, I'd say fine, stick to it !

Now let's look at Alex's test. He used a larger fast Newtonian. Aside from whatever the eyepieces are doing, the diffraction-limited field of view in his scope is tiny - smaller than the FoV of the 13mm eyepieces for sure. Secondly the aperture of his scope means he wouldn't have come anywhere near the diffraction limit from his home. Then there is a question as to vignetting due to the secondary mirror - most fast Newtonians have secondaries that are somewhat undersize simply to avoid them exceeding 30% of the aperture of the primary - and lastly collimation - fast Newtonians are very sensitive to this.

Consequently any conclusions concerning off-axis performance of the eyepiece I would tend to take with a grain of salt because the effects of off-axis degradation due to the scope.

FWIW for a while I used an even more extreme 'scope - a 32 cm f/3.7 Newtonian - and knew all about what was wrong with fast Newts.

If you want tack sharp images at medium to high magnification nothing beats good-ol LONG LONG LONG FOCAL LENGTH, with a small secondary obstruction (none if it's a refractor) and virtually any eyepiece will perform well, apart from contrast.

Ultimately... this is why my current scopes are an f/7 refractor and f/15 Mak, and in some respects I dream of one of these http://www.skylightelescopes.co.uk/. Maybe one day when I can afford a decent mount, and the country house to go with it.

Last edited by Wavytone; 30-04-2012 at 12:05 AM.
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  #30  
Old 30-04-2012, 10:07 AM
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Choosing eyepieces is an area where there are too many conflicting variables, about which most of us have little or no real information to make a decision. That leaves 'trying before buying' or pot luck.[/QUOTE]
Hi all,
This from Wavytone sums it up for me pretty well. Obviously an area where lots of cash wins every time...so while waiting for the long lost uncle's inheritance to turn up it's time to let it all sink in, and for the moment, stick with my GSO plossls and ES eyepieces. Some really good things in this thread thanks all ...wow such a simple question, or so I thought. Wavytone a very nice bunch of scopes from skylight too...also dreaming of a long refractor in the country...
Matt
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  #31  
Old 30-04-2012, 11:21 AM
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Matthew, yeah, who would have thought from "such a simple question", !

Wavy's brought up another point - the lack of information on the matching optical properties of different scopes vs those of eyepieces. Newtonians, Maks, refractors, SCT's, these have different properties inherent to them, to not even mention differences between f/ratios in each lot. Different EPs perform differently in each scope type. You will never read in a manufacturer's literature that a particular EP of their's performs poorly in any scope type. It's bull to think that any one EP will be as good in an f/3.7 Newt. as it will an f/15 Mak.

A new RKE which uses ED glass types? I'm in for using it in my fast Newts! 30mm to 5mm, 68 degree FOV, three elements, good eye relief, down to peanut sized, no astigmatism and deals with coma! Brilliant. More like dreaming...
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  #32  
Old 03-05-2012, 07:05 PM
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I have the LVW22mm.
On my 10" dob which is a fast scope at 4.7, it performs exceptionally well. Pin point, crisp stars right to the edge. It's one of my favorite eyepieces.

Quote:
mental4astro

First, I can't make an appology for what I saw down the eyepiece
Ya should, you in real trouble, this is war mister!

That's actually the first I've heard of a Hyperion trumping an LVW, but as pointed, much has to do with the telescope. I have a fast newt as well, but obviously mirror size etc has to be taken into consideration.

So... the bigger the scope, the cheaper the eyepiece, lol.
Sorry, I couldn't resist, forgive me, I mean no harm. I'm kidding, really I am... eeeeeek
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  #33  
Old 03-05-2012, 07:12 PM
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Quote:
Originally Posted by madbadgalaxyman View Post

I note, however, that maximizing the contrast between the object and the surrounding field, also can improve the observer's view of a deep sky object. On stellar and non-stellar deep sky objects, the particular Nagler eyepiece that I mentioned had considerably superior contrast to the LVW I tested, to such a large extent that the difference was blatantly obvious even after a few seconds viewing;
but exactly what combination of smaller star images and/or greater light transmission and/or a smaller amount of scattered light, was actually the cause of this noticeably better performance by the 20mm typeII Nagler..... I do not know.

cheers, bad galaxy man
Hi Robert,

The Naglers have got a "coffee tone" colour to them as opposed to XW's for instance that are neutral.
Some people like the colour tone of the Naglers, while some find it annoying as being a false colour tone on stars. I wouldn't know, I don't own a Nagler, but I've read plenty on the "coffee tone" aspect of it.
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Old 03-05-2012, 07:31 PM
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Hi Robert,

The Naglers have got a "coffee tone" colour to them as opposed to XW's for instance that are neutral.
Some people like the colour tone of the Naglers, while some find it annoying as being a false colour tone on stars. I wouldn't know, I don't own a Nagler, but I've read plenty on the "coffee tone" aspect of it.
Suzy, as you know I have 3 Naglers, I am looking forward to comparing eyepieces.
I have never as far as I know looked through an XW so it should be an interesting exersize .
Cheers
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  #35  
Old 04-05-2012, 11:49 AM
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Quote:
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Hi Robert,

The Naglers have got a "coffee tone" colour to them as opposed to XW's for instance that are neutral.
Some people like the colour tone of the Naglers, while some find it annoying as being a false colour tone on stars. I wouldn't know, I don't own a Nagler, but I've read plenty on the "coffee tone" aspect of it.
I admit, Suzy, that I have never paid much attention to the colour tone of eyepieces.

I have a nagging feeling that certain specific so-called "fully coated" eyepieces actually do have an uncoated air-glass surface that is hiding somewhere inside the eyepiece. A single uncoated glass surface usually reflects 3-4 percent of the light that hits it, instead of transmitting that light;
which, in itself, is probably too small a brightness difference for the eye to notice.
BUT - certain glasses of high refractive index can reflect 6-8 percent of the light hitting an uncoated air-glass surface.

I do think that 6-8 percent could be a visually noticeable loss of the light that ought to be reaching the eye, if one takes into account the fact that the unwanted reflected light is going somewhere into the field, instead of into the image of the object.....thereby leading to a loss of contrast between the light from the object and the light coming from the field (the light in the field has a measurable value)

For a couple of years, I was totally obsessive about visually observing vanishingly faint emission nebulae......and I did find that the various small & not-so-small losses of light taking place in the optical train actually did make a difference to the quality of the views of these very challenging objects that are at or near the fringes of visibility.

cheers, robert
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  #36  
Old 05-05-2012, 01:15 AM
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I have noticed the ' coffee tone ' in my 8mm Radian , but that dissapares soon after using it , then its real strengths come into play , great eyepiece . The coffee tone does not worry me at all , and I have compared my 8mm Radian with my , 9mm Orthoscopic , 9 and 10mm Vixen Lanthium's and my Baader 9mm ' real' ortho , and they all have their strenght's . and I love them all .
On the Nagler coffee tone , I have not seen it in mine , I will look for it now , but it must be very slight ..
Brian .
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  #37  
Old 05-05-2012, 02:10 PM
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LVW for me.
But I reckon ES ep are better value.
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  #38  
Old 06-05-2012, 09:36 PM
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Quote:
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I have noticed the ' coffee tone ' in my 8mm Radian , but that dissapares soon after using it , then its real strengths come into play , great eyepiece . The coffee tone does not worry me at all , and I have compared my 8mm Radian with my , 9mm Orthoscopic , 9 and 10mm Vixen Lanthium's and my Baader 9mm ' real' ortho , and they all have their strenght's . and I love them all .
On the Nagler coffee tone , I have not seen it in mine , I will look for it now , but it must be very slight ..
Brian .

Apparently you can tell (so I've read) if you compare it with a neutral tone ep and the warmer tone of a Nagler on the moon.

The warm colour of the Nagler (so I've read) is great for planetary observing as on Jupiter's belts- so there is a plus.
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10x IceInSpace Stickers