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Equipment Discussions >> Eyepieces

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Paul G
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Reged: 05/08/03

Loc: Freedonia
Re: Eypiece transmission new [Re: Eddgie]
      #5568758 - 12/13/12 07:23 AM

Quote:

Here is an example from this thread that corresponds to the post I just made.

If the TV Nagler 13 mm II has 87.3% transmission, to be seen as 10% brighter, you would add 10% to that figure, or 8.73% in relative terms. So adding 10% of the 87.3% means that any eyepice with 96.03% transmission would be 10% brighter on a relative scale.




That's not how our visual system works. If you increase transmission 10% the difference would be barely detectable, some would see a slight difference, others wouldn't see a change. It's a physiological phenomenon called response compression. For example, for a point light source or an extended object to be seen as 100% brighter its intensity would have to be increased about 900%.


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tomharri
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Reged: 09/19/08

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Re: Eypiece transmission new [Re: Paul G]
      #5568791 - 12/13/12 08:12 AM

I think you guys are just looking at your eyepieces and not looking thru them. The 6mm Delos shows so much more on Jupiter than the latest ortho, the Kasai, that it is no contest. When you put the Delos in, it's like you just put your glasses on. Jupiter is sharper-clearer-more contrasty, put in any positive adjective you can think of, it is so much better, plus you have 70 degrees to play with. Ever since I bought my first Pentax XW, and now the Delos, they both are superior visually, just like the Zeiss, over anything else out there.

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Sarkikos
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Re: Eypiece transmission new [Re: tomharri]
      #5568823 - 12/13/12 08:41 AM

I don't think Jupiter - or any other bright planet - is a good test of transmission. For that you need to look at deep sky objects. IMO, the best light-transmission field test would involve detecting objects near the limiting magnitude of the telescope.

Even detecting faint moons of a bright planet is not the best test of transmission. In that case, it's too easy to confuse the effects of light scatter with light transmission. Best to keep it simple.

Mike


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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission [Re: ThomasM]
      #5781768 - 04/06/13 12:32 PM

A short update, here are transmissions for 532 nm:

Kasai HC Ortho 12 mm, 97.8%
Baader Classic Ortho 10 mm, 97 %
Paradigem 8 mm, 90,5 %

in addition I measured the transmission at 405 nm

Kasai HC Ortho 12 mm, 89%
Baader Classic Ortho 10 mm, 95 %
TMB ED 1.8x barlow, 94,5%

regards

Thomas


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Eypiece transmission [Re: ThomasM]
      #5781904 - 04/06/13 01:49 PM

Quote:

A short update, here are transmissions for 532 nm:

Kasai HC Ortho 12 mm, 97.8%
Baader Classic Ortho 10 mm, 97 %
Paradigm 8 mm, 90,5 %

in addition I measured the transmission at 405 nm

Kasai HC Ortho 12 mm, 89%
Baader Classic Ortho 10 mm, 95 %
TMB ED 1.8x barlow, 94,5%

regards

Thomas



What this points out is that if the eyepiece is inexpensive, the absolute state-of-the-art coatings are unlikely to be applied.
If they were, the transmissions at 532nm would have read 98%, 98%, and 96% respectively.
The very high-end brands also multi-coat the lens surfaces that are cemented to increase transmission and reduce internal scatter.

This also shows that transmission spectra differ from eyepiece to eyepiece.

One of the things I found remarkable about TeleVue's newer Ethos and Delos eyepiece types was the improved red transmission. Whether this was simply due to improved transmission over the Nagler series, or actually represented a different curve of transmission (my suspicion), I don't know, but it points out how somewhat different transmission levels at the extremes may influence one's perception of "tint" in the eyepiece.


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Shneor
scholastic sledgehammer
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Reged: 03/01/05

Loc: Northern California
Re: Eypiece transmission [Re: denis0007dl]
      #5782141 - 04/06/13 04:25 PM

Quote:

It would be interesting to test Explore Scientific 68" and 82" eyepieces



Not to mention the ES100° and 120° eyepieces...

Clears,


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ThomasM
sage


Reged: 04/19/09

Re: Eypiece transmission [Re: Starman1]
      #5782233 - 04/06/13 05:21 PM

Quote:

Quote:

A short update, here are transmissions for 532 nm:

Kasai HC Ortho 12 mm, 97.8%
Baader Classic Ortho 10 mm, 97 %
Paradigm 8 mm, 90,5 %


Thomas



What this points out is that if the eyepiece is inexpensive, the absolute state-of-the-art coatings are unlikely to be applied.
If they were, the transmissions at 532nm would have read 98%, 98%, and 96% respectively.
The very high-end brands also multi-coat the lens surfaces that are cemented to increase transmission and reduce internal scatter.

This also shows that transmission spectra differ from eyepiece to eyepiece.

One of the things I found remarkable about TeleVue's newer Ethos and Delos eyepiece types was the improved red transmission. Whether this was simply due to improved transmission over the Nagler series, or actually represented a different curve of transmission (my suspicion), I don't know, but it points out how somewhat different transmission levels at the extremes may influence one's perception of "tint" in the eyepiece.




Actually, I think the simple rule of 1% loss per single element does not apply for short focal lenght Orthos, typially the transmission is less by 1-2%, I have no idea if it is an artefact of the measurement or if it is real, but this trend can also be seen here:

http://www.amateurastronomie.com/Astronomie/tips/tips3.htm

The transmission of a 12 mm Ortho with an excellent Barlow, such as the TMB ED is better than that of an 7 mm Orho, while at the same time it is much more comfortable to use.

Thomas

p.s. I was not aware of the high transmission of the Ethos eyepieces in the red, are there any results published?


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alancygnusx2
professor emeritus


Reged: 11/25/08

Loc: CA
Re: Eypiece transmission [Re: ThomasM]
      #5782334 - 04/06/13 06:15 PM

Hi Thomas,

Thanks for posting your transmission measurements.

Regarding multicoatings there is a nice article by Rodger Gordon who was an optical engineer for unitron.

The article is here:

Multicoatings


Multicoatings can not only absorb some of the spectrum, but can also cause narrow angle scattering, which has already been mentioned above in this thread.

It would be interesting to shine lasers of different wavelenghts through each eyepiece and have the resulting spot projected onto a distant wall to see how much scattering there is, and to see if it varies between eyepieces.


Alan

Edited by alancygnusx2 (04/06/13 06:17 PM)


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Eypiece transmission [Re: alancygnusx2]
      #5782378 - 04/06/13 06:37 PM

Sigh.
This old canard again.
If you truly appreciate HOW a multicoating enhances transmission, then you would appreciate that IF the multicoating layers are chosen correctly (and they are in tandem with the refractive index of the glass they coat), then this so-called "narrow angle light scatter" cannot occur (or, if you will, what level of it occurs could not possibly be visible to the eye). It will be the axial ray that has the highest transmission, least reflection and scatter, and it is the more oblique rays that are more likely to scatter and/or be changed in spectrum.

Of course, it's certainly possible that inexpensive multi-coatings may not be the proper materials to produce the best transmission (leading to more reflection), and it may be that, applied to poorly-polished surfaces, they don't help enough to reduce what scatter would have been already there.

But note that all such "reports" are anecdotal, and they are usually suspect for the same reason global climate change reports from coal companies are suspect--the principals have a stake in the end result of such an "examination of evidence".

And it is interesting to note that many of the eyepieces that are the most highly-regarded eyepieces made are and were multi-coated throughout. In fact, several such eyepieces are known for having NO light scatter, either on or off axis.


As for the previous point that you can count on 1% light loss per element, this is no longer true. Some 8-element eyepieces with 10 air-to-glass surfaces transmit more than 96% and some 9-element eyepieces are in the same range. It does, however, depend on the coatings chosen, and those particular eyepieces would have lost prodigious amounts of light were it not for the use of expensive multicoatings on every glass surface. Nikon even has some professional 20-element photographic lenses that transmit somewhere in the 96-97% range. We could never afford those coatings in telescope eyepieces, but it goes to show that modern multi-coatings are a far cry from the multicoatings of yesteryear.


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Scanning4Comets
Markus
*****

Reged: 12/26/04

Loc: Ontario, Canada
Re: Eypiece transmission [Re: Starman1]
      #5782686 - 04/06/13 09:46 PM

Quote:

As for the previous point that you can count on 1% light loss per element, this is no longer true. Some 8-element eyepieces with 10 air-to-glass surfaces transmit more than 96% and some 9-element eyepieces are in the same range. It does, however, depend on the coatings chosen, and those particular eyepieces would have lost prodigious amounts of light were it not for the use of expensive multicoatings on every glass surface. Nikon even has some professional 20-element photographic lenses that transmit somewhere in the 96-97% range. We could never afford those coatings in telescope eyepieces, but it goes to show that modern multi-coatings are a far cry from the multicoatings of yesteryear.






So true Don! In this day & age, we have a wealth of them to choose from as well.



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alancygnusx2
professor emeritus


Reged: 11/25/08

Loc: CA
Re: Eypiece transmission [Re: Starman1]
      #5782754 - 04/06/13 10:12 PM

I have no doubt that the ZAO IIs have multicoatings which cause close to zero scatter. I'd like to to see data on other eyepieces before I assumed their multicoatings were as good as the ones on the Zeiss. There's a big difference between knowing how to do it well and being able to do it well, and within price constraints that the amateur market will bear.

When I purchased a ball eyepiece from Harry Siebert, we were talking about coatings, he mentioned to me that there are eyepieces currently on the market that do not transmit evenly across the full visual spectrum due to their multicoatings. One would think that should be a thing of the past, but it isn't. Optics is a nuanced field, I wouldn't take anything for granted.

If you feel narrow angle scatter is a canard, I would appreciate a good link or a reference with data showing otherwise. My intention in making my previous post was to be helpful to Thomas. As far as I know Rodger Gordon was extremely well respected for his work.

Edited by alancygnusx2 (04/06/13 11:02 PM)


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buddyjesus
Carpal Tunnel
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Reged: 07/07/10

Loc: Davison, Michigan
Re: Eypiece transmission [Re: alancygnusx2]
      #5782992 - 04/07/13 01:11 AM

very informative thread. thanks guys

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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Eypiece transmission [Re: alancygnusx2]
      #5783057 - 04/07/13 02:45 AM

Quote:

I have no doubt that the ZAO IIs have multicoatings which cause close to zero scatter. I'd like to to see data on other eyepieces before I assumed their multicoatings were as good as the ones on the Zeiss. There's a big difference between knowing how to do it well and being able to do it well, and within price constraints that the amateur market will bear.

When I purchased a ball eyepiece from Harry Siebert, we were talking about coatings, he mentioned to me that there are eyepieces currently on the market that do not transmit evenly across the full visual spectrum due to their multicoatings. One would think that should be a thing of the past, but it isn't. Optics is a nuanced field, I wouldn't take anything for granted.

If you feel narrow angle scatter is a canard, I would appreciate a good link or a reference with data showing otherwise. My intention in making my previous post was to be helpful to Thomas. As far as I know Rodger Gordon was extremely well respected for his work.



Follow this thread:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3457819/Main...
and this one:
http://tech.groups.yahoo.com/group/tec-scopes/message/14857
There is no agreement among very respected sources.
I mentioned this once to a friend of mine who designs lenses for the military and he mentioned he'd heard of it but that the effect was "irrelevant" when "coating materials were properly chosen for the index of refraction".
And the conversation I had one afternoon with the Nikon engineers who design coatings on lenses to maximize transmission only mentioned the positive effects of superior coatings for transmission, reduction of scatter ,and improved contrast.

As for Siebert's comments, he's right. Also, uncoated eyepieces don't transmit flat across the visible band, either. And neither do simple MgFl2 coatings. or aluminum coatings on mirrors, etc. I have done literally thousands of hours of observing through hundreds of scopes and hundreds of different eyepieces over 50 years. And the only "narrow angle light scatter" I've ever seen was color in refractors (aka chromatic aberration).
Oh, I've seen scatter all right--that caused by haze in the atmosphere, dew on the optics or lenses, rough optical surfaces, light reflection internal to the scope and eyepiece, uncoated lenses, dust on optical surfaces, spherical aberration, uncorrected fields, aberrations of multiple kinds, etc. etc.

I side with Roland Christen on this one. Superior multi-coatings make possible superior contrast, not poorer contrast.


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alancygnusx2
professor emeritus


Reged: 11/25/08

Loc: CA
Re: Eypiece transmission [Re: Starman1]
      #5783082 - 04/07/13 04:22 AM

Quote:

Quote:

I have no doubt that the ZAO IIs have multicoatings which cause close to zero scatter. I'd like to to see data on other eyepieces before I assumed their multicoatings were as good as the ones on the Zeiss. There's a big difference between knowing how to do it well and being able to do it well, and within price constraints that the amateur market will bear.

When I purchased a ball eyepiece from Harry Siebert, we were talking about coatings, he mentioned to me that there are eyepieces currently on the market that do not transmit evenly across the full visual spectrum due to their multicoatings. One would think that should be a thing of the past, but it isn't. Optics is a nuanced field, I wouldn't take anything for granted.

If you feel narrow angle scatter is a canard, I would appreciate a good link or a reference with data showing otherwise. My intention in making my previous post was to be helpful to Thomas. As far as I know Rodger Gordon was extremely well respected for his work.



Follow this thread:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3457819/Main...
and this one:
http://tech.groups.yahoo.com/group/tec-scopes/message/14857
There is no agreement among very respected sources.
I mentioned this once to a friend of mine who designs lenses for the military and he mentioned he'd heard of it but that the effect was "irrelevant" when "coating materials were properly chosen for the index of refraction".
And the conversation I had one afternoon with the Nikon engineers who design coatings on lenses to maximize transmission only mentioned the positive effects of superior coatings for transmission, reduction of scatter ,and improved contrast.

As for Siebert's comments, he's right. Also, uncoated eyepieces don't transmit flat across the visible band, either. And neither do simple MgFl2 coatings. or aluminum coatings on mirrors, etc. I have done literally thousands of hours of observing through hundreds of scopes and hundreds of different eyepieces over 50 years. And the only "narrow angle light scatter" I've ever seen was color in refractors (aka chromatic aberration).
Oh, I've seen scatter all right--that caused by haze in the atmosphere, dew on the optics or lenses, rough optical surfaces, light reflection internal to the scope and eyepiece, uncoated lenses, dust on optical surfaces, spherical aberration, uncorrected fields, aberrations of multiple kinds, etc. etc.

I side with Roland Christen on this one. Superior multi-coatings make possible superior contrast, not poorer contrast.





As BillP lists in the thread, there are many scientific papers explaining the phenomenon of low angle scatter. A canard is a false and baseless story, it doesn't seem like that word should be used to describe a phenomenon that has backing from scientific publications as well as some serious experts in optics.

Thomas Back specifically mentioned he measured low angle scatter on his coatings for his monocentrics and thought they were the lowest scatter he had seen on multicoated eyepieces.

You mention you haven't seen any scatter, but Chris Lord reports that the effect would be a reduction in contrast between contrast boundaries.

How is it that a simple uncoated bk7 ball lens performs as well on the planets on axis as the best planetary eyepieces available?

At the very highest levels of performance, I will guess that unless significant expense in getting multicoatings applied using the best technology, there is the potential for degradation of the image.

Our problem as amateurs is that we don't have the equipment to objectively measure things like narrow angle scatter for ourselves.

Edited by alancygnusx2 (04/07/13 04:24 AM)


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Jeff Morgan
Postmaster
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Reged: 09/28/03

Loc: Prescott, AZ
Re: Eypiece transmission [Re: Starman1]
      #5783639 - 04/07/13 11:52 AM

Quote:

I side with Roland Christen on this one. Superior multi-coatings make possible superior contrast, not poorer contrast.




Indeed, doing a search on the Yahoo AP turns up many postings by Roland Christen on eyepiece coatings, contrast, and performance from the point of a optician and purist. Coatings of course being only one element of eyepiece performance. Extrapolating from "superior coating" to "superior eyepiece" would be a logical error. But it's certainly a good place to start.

It would appear that RC was of the opinion that while a few commercial eyepieces might do it well, only Zeiss was doing it correctly.


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Jeff Morgan
Postmaster
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Reged: 09/28/03

Loc: Prescott, AZ
Re: Eypiece transmission [Re: alancygnusx2]
      #5783673 - 04/07/13 12:12 PM

Quote:

Our problem as amateurs is that we don't have the equipment to objectively measure things like narrow angle scatter for ourselves.




Indeed, that is the crux of the problem.

I have seen first-hand how the 13 Ethos had better transmission than my T4 Naglers. And I am definitely a Delos enthusiast with three of them in my eyepiece case. But on the planets and double stars, I love the performance of my MgFL coated Brandons. With my only test equipment being the Mk-I eyeball there is no way of telling if it is because of the coatings, or in spite of the coatings. The only clue is that Don Yier did trial multi-coatings and elected not to do them on a performance basis.

I do know the end result, which keeps repeating itself across nights and telescopes. If it weren't the case I would be Astromarting those Brandons in a heartbeat for other eyepieces.


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alancygnusx2
professor emeritus


Reged: 11/25/08

Loc: CA
Re: Eypiece transmission [Re: Jeff Morgan]
      #5783928 - 04/07/13 02:29 PM

Hi Jeff,

Thank you for your comments, and also including a link to Roland's post,

I see he indicates quite clearly that eyepiece multicoatings do not automatically mean high contrast and high transmission, and suboptimal adjustment of the coatings to each glass type in the elements is the cause.


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Jeff Morgan
Postmaster
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Reged: 09/28/03

Loc: Prescott, AZ
Re: Eypiece transmission [Re: alancygnusx2]
      #5784208 - 04/07/13 04:16 PM

Quote:

Hi Jeff,

Thank you for your comments, and also including a link to Roland's post,

I see he indicates quite clearly that eyepiece multicoatings do not automatically mean high contrast and high transmission, and suboptimal adjustment of the coatings to each glass type in the elements is the cause.




Yes, reading Roland's posts are like a graduate-level course. The more of his posts you read the more you realize that all this focus on coatings is barking up the wrong tree.

The big issues are the glass count (since glass scatters light by it's very nature), dirt between the elements, pits (polish), and dirt on the eye and field lens.

Of these, it appears he views contaminants between the lenses as the worst offender. The best contrast comes from the cleanest internals, which means lenses individually hand-assembled by a very picky craftsman. Three manufacturers come to mind in this regard: Zeiss, Astro-Physics (the short lived SPL line), and Brandon.


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Eypiece transmission [Re: Jeff Morgan]
      #5784319 - 04/07/13 05:07 PM

Quote:

Quote:

Hi Jeff,

Thank you for your comments, and also including a link to Roland's post,

I see he indicates quite clearly that eyepiece multicoatings do not automatically mean high contrast and high transmission, and suboptimal adjustment of the coatings to each glass type in the elements is the cause.




Yes, reading Roland's posts are like a graduate-level course. The more of his posts you read the more you realize that all this focus on coatings is barking up the wrong tree.

The big issues are the glass count (since glass scatters light by it's very nature), dirt between the elements, pits (polish), and dirt on the eye and field lens.

Of these, it appears he views contaminants between the lenses as the worst offender. The best contrast comes from the cleanest internals, which means lenses individually hand-assembled by a very picky craftsman. Three manufacturers come to mind in this regard: Zeiss, Astro-Physics (the short lived SPL line), and Brandon.



And TeleVue, for both cleanliness and coatings. Lens count can't explain everything or the 9 element Ethos wouldn't beat the 7 element Naglers, but they do.
Dirt on or near the focal plane of the eyepiece is the worst place to see it. External dirt can be cleaned off (I recommend ROR).


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Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: Eypiece transmission [Re: Starman1]
      #5785175 - 04/08/13 01:25 AM

Quote:


And TeleVue, for both cleanliness and coatings. Lens count can't explain everything or the 9 element Ethos wouldn't beat the 7 element Naglers, but they do.
Dirt on or near the focal plane of the eyepiece is the worst place to see it. External dirt can be cleaned off (I recommend ROR).




And so they do, I've seen it myself. Extra effort (money) can largely overcome inherent handicaps. In the end it's results with the Mk-I eyeball that pays the bills. (Or more accurately, creates new credit card bills.) I'm quite happy with my Delos and Brandons. Different approaches, excellent results in both cases. There certainly is more than one way to skin the cat.

With any luck Tele Vue is leveraging the Delos experience and diligently working on focal lengths above 22 mm, perhaps a Panoptic Type 2 or Nagler Type 7.

Thanks for bringing RC up, I enjoyed re-reading his views on eyepieces. One tends to forget fundamentals over time. Perhaps the best quote was (to paraphrase): you can buy $9 worth of eyepieces from the Far East, but that does not mean you get $9 worth of glass.


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