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Eyepiece Musings: Transmission Values

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#1 RLK1

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Posted 04 June 2020 - 03:57 PM

I'm interested in obtaining representative light transmission percentages for some of the eyepieces in my collection so I did some digging in CN and elsewhere and came up with some information. While I realize the values may not be specific to each iteration of ocular, I'm particularly interested in those above 95% and the latter is an arbitrary demarcation a CN reviewer used in his determination of values for various 1.25" eyepieces.  Of the many that he tested, I find those in my collection to make the cut:

1 UO Ortho 25mm @ 97.3%

2 UO Ortho 18mm @ 95.7%

3 BGO Otho 9mm @ 95.7%

4. Orion Ultrascopic 25mm @ 95.5%

Those in my collection for which I could find data on and below 95%:

1 ES 9mm 100 @ 91.1%

Those in my collection that I'm seeking data on:

1 Ethos 10mm

2. UO ortho 12.5mm

3 UO ortho 6mm

4. Pentax 10.5mm 65 AFOV

5 Speers Waler 10mm 

6 ES 14mm 100

7 ES 30mm 82

8 ES24mm 82

9 Paradigm/astroguider 18mm

 

PS: Generalizations: The following series all reportedly have about the same measured levels of transmission: Pentax XWs/Delos/ BGO Orthos @95% or slightly higher. 13mm @ 17mm Ethos variable findings but averaging around 93%. Nagler T6 7 &13mm @ 87%(measured by two different reviewers).

I could find one measurement of a paradigm ocular: 8mm @ 90.5%. Expect to find some variation on the specifics of the tests employed by those making the determinations.


Edited by RLK1, 04 June 2020 - 05:33 PM.


#2 SeattleScott

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Posted 04 June 2020 - 04:10 PM

Nagler T7? Is that the Apollo 11? I would have expected better.

Personally I don’t know that transmission is that critical for orthos as most people use them on bright objects. But they have pretty good transmission anyway due to fewer elements.

Overall I wouldn’t obsess too much about transmission. Are you really going to see the difference between 97% and 95% or 93%? Becomes a bigger deal with 87% but presumably that is an old eyepiece with old coating technology.

Scott

#3 junomike

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Posted 04 June 2020 - 04:46 PM

IME the more glass equates to less transmission however there can be more at play with coatings and polish.


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#4 RLK1

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Posted 04 June 2020 - 04:46 PM

Nagler T7? Is that the Apollo 11? I would have expected better.

Personally I don’t know that transmission is that critical for orthos as most people use them on bright objects. But they have pretty good transmission anyway due to fewer elements.

Overall I wouldn’t obsess too much about transmission. Are you really going to see the difference between 97% and 95% or 93%? Becomes a bigger deal with 87% but presumably that is an old eyepiece with old coating technology.

Scott

I went back and modified my post and it now states, T6 7&13mm naglers. Thanks for catching that. Since I don't know what the transmission values are for the eyepieces in question, I can't assume it's less or more than one value versus another. I hope to have specific information on it.



#5 photoracer18

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Posted 04 June 2020 - 04:47 PM

Well the Pentaxes have their 7 layer SMC coatings on all air to glass surfaces. SMC has a transmission of 99.84% per air to glass surface so its simple multiplication. Obviously the number of optical groups affects the results. With an old style eyepiece such as a Plossl, Ortho, Kellner and Ramsden you have 4 AGS so the Pentax SMC O eyepieces will have a transmission of 99.36% (99.84 to the 4th power). They would be at the top of any list as solid eyepieces like Tolles, Hastings, and Monocentrics with 2 AGS don't have coatings near that good. I am pretty sure its hard to tell a few points difference with the human eye so its not really high on my list even though I do have a set of older Pentax XL eyepieces. The eyepiece design is more important.

 

The Pentax XW have either 4 or 6 optical groups. 4 equals 8 AGS and 6 equals 12 AGS (XL are similar) so 4 groups would be 97.47% and 6 would be 90.25%. Any other eyepiece (with the exception of Zeiss) will be lower than that for the same number of groups because its not possible to get the same transmission with fewer layers. I mention Zeiss because of the history of lens coatings when they teamed with Pentax back in the 50's. Every other camera companies lenses except Leica derived from that original technology as they sold both full and partial licenses of the technology to the other makers. That was in the days just before the big 4 Japanese camera companies had cross-licensing agreements.


Edited by photoracer18, 04 June 2020 - 05:11 PM.

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#6 RLK1

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Posted 04 June 2020 - 05:00 PM

Well the Pentaxes have their 7 layer SMC coatings on all air to glass surfaces. SMC has a transmission of 99.84% per air to glass surface so its simple multiplication. Obviously the number of optical groups affects the results. With an old style eyepiece such as a Plossl, Ortho, Kellner and Ramsden you have 4 AGS so the Pentax SMC O eyepieces will have a transmission of 99.36% (99.84 to the 4th power). They would be at the top of any list as solid eyepieces like Tolles, Hastings, and Monocentrics with 2 AGS don't have coatings near that good. I am pretty sure its hard to tell a few points difference with the human eye so its not really high on my list even though I do have a set of older Pentax XL eyepieces. The eyepiece design is more important.

My reference to pentax XWs in my initial post being comparable to the BGOs/Delos series is based upon a prior CN thread on the eyepiece transmission:

"It looks like 96% transmission for the XW's at 550 nm. Judging from the graph, the transmission at 532 nm should be not much less than that, certainly no less than 95%. According to focal length, the XW's vary between about 95% and 96% transmission. So the XW's transmission is closely comparable to the Delos and BGO's."



#7 MartinPond

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Posted 04 June 2020 - 10:35 PM

I think in a blinded taste-test nobody could tell the difference.

The eye receptors are logarithmic gadgets.

First lab I had in optics.

How the actual design deals with stray light and light

   surface contamination is vastly more important, IMO.

It's something to compare and brag about, though.


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#8 SeattleScott

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Posted 04 June 2020 - 10:49 PM

I think in a blinded taste-test nobody could tell the difference.
The eye receptors are logarithmic gadgets.
First lab I had in optics.
How the actual design deals with stray light and light
surface contamination is vastly more important, IMO.
It's something to compare and brag about, though.

My thoughts exactly. There is one eyepiece I sold because of poor transmission. But it was decades old, older technology, likely worn coatings. Typically I don’t notice any difference in transmission between my eyepieces. Controlling light scatter, field curvature astigmatism, lateral color, those are what I really look for in a eyepiece.

Scott

#9 Starman1

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Posted 05 June 2020 - 12:02 AM

Some eyepiece transmission links:

http://www.cloudynig...ons of mine.pdf
http://www.cloudynig...ransmission.txt
http://www.cloudynig...eces/img13.html
http://www.amateuras.../tips/tips3.htm
http://www.cloudynig...eces/img14.html


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#10 RLK1

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Posted 05 June 2020 - 12:05 AM

My thoughts exactly. There is one eyepiece I sold because of poor transmission. But it was decades old, older technology, likely worn coatings. Typically I don’t notice any difference in transmission between my eyepieces. Controlling light scatter, field curvature astigmatism, lateral color, those are what I really look for in a eyepiece.

Scott

While I look for those factors as well, I'd just as soon have an eyepiece with greater transmission rather than less...



#11 Starman1

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Posted 05 June 2020 - 12:06 AM

Some things to know:

--the curve of transmission is as important as its height.

If a transmission test doesn't measure at at least 5 wavelengths, it won't tell you much.

--a 10% difference only represents 0.1 magnitude.  That's less than the hour-to-hour change in the sky brightness.

And about the limit of human vision in a lab, not the field. 

After all, the typical reflector has a light loss of 30% at the edge of the field in a low power eyepiece, and we don't notice it.


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#12 RLK1

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Posted 05 June 2020 - 12:12 AM

Thanks for the links. I had seen some but not all of these.



#13 SeattleScott

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Posted 05 June 2020 - 12:45 AM

While I look for those factors as well, I'd just as soon have an eyepiece with greater transmission rather than less...

True, all other things equal, greater transmission is better.
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#14 Jon Isaacs

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Posted 05 June 2020 - 01:15 AM

I went back and modified my post and it now states, T6 7&13mm naglers. Thanks for catching that. Since I don't know what the transmission values are for the eyepieces in question, I can't assume it's less or more than one value versus another. I hope to have specific information on it.

 

Do you have references? The numbers I've seen for the T6 Naglers are much higher than that, around 94%.

 

Edit:

 

I see Don posted some links, they seem consistent with what I remember for the T-6s.

 

These are Markus Ludes's numbers:

 

TV Nagler 5mm type 6 90.79 91.83 95.24 96.86 94.11 96.96 at 596 nm
TV Nagler 7mm type 6 90.37 91.34 94.27 96.33 94.69 96.55 at 610 nm

 

Jon



#15 25585

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Posted 05 June 2020 - 04:50 AM

Pentax the OP listed is the XL that was succeeded bya 10mm XW, that had 5° more AFOV. 

 

This is a very good comparison of both. https://docplayer.ne...ts-com-com.html

 

The XW transmission is said to be 98%, but read the full article.


Edited by 25585, 05 June 2020 - 05:02 AM.

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#16 MartinPond

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Posted 05 June 2020 - 08:05 AM

True, all other things equal, greater transmission is better.

 

It is confusing, then when none of those other "things" are compared

  here  at the same time.

 

   And...if this is your first priority, it can easily be "gamed".

Don mentioned how you have to consider different wavelengths. Otherwise,

someone would design and promote the lowest green loss at the expense of 

 red and violet.   For electromagnetically similar reasons, losses on center

 can be optimized whilst even more quickly inducing poor transmission

  at the edges of the field.   I remember looking at some ProMaster binoculars

  that claimed stunningly low losses.  I was confused when I saw a noticeable

   dimming at the field edges.  Then the "aha!" moment:  they described a 20-layer

  coating process.   That's inevitably a great thickness, and a narrow spectral

  optimum, and an even narrower optimum across the field, in the eyepiece elements.

 

All else is usually...not equal.

 

I have a target with fading densities printed out on the paper.

The faintest printed line has RGB values of 225-each..

 

Now, the 18mm  Paradigm Dual-ED is acknowledged generally

   as great for the money, and it is fully multi-coated. I love it myself.

 

 And...the 18mm Kellner from the Zeiss Silvarem 6x30s of ~1915

 can see more letters as they fade in and out from irregular printing

     (awesome accidental feature) than the Paradigm.

This is not to specifically knock the Paradigm, but the differences

   are extensive when it comes to coating.   The Zeiss...has none.

   It has 4 glass-air surfaces, of course.

Life was not made easy on the Zeiss Kellner, btw: 

    both eyepieces were checked at F5.

 

And in the sky, at least a few times, more subtle detail 

    was available with the ancient Zeiss on M16 (Eagle Nebula),

    which is easy to see, but has different appearances depending

    on your brightness and contrast......

 

What isn't equal?  Mainly the number of elements.

 

Oddly enough (or not), Zeiss cameras and microscopes and eyepieces

  have around 7 layers coating, and less super-transmission

   the others.   They stick with it, though, because racing for

   'my transmission is better than yours' leads to trouble.

  I would strive for low losses, but avoid the lowest transmission losses

     like the Plague.

 

One thing that is  quite probably true is that eyepieces with many elements

    wouldn't be very good without multi-coating. But it's also true that

    multi-coating is a Hi-Q filter, basically, and because it is Hi-Q ,

    it is extremely sensitive to surface contamination. You can't avoid

    that at the first and final air surfaces.  Another problem is that, for example,

    an Abbe naturally and easily tosses off out-of-field scattering, whereas

     this is a lot more difficult  to design with many elements and wider angles.

 

So...thus we have the roots of the debate over 

    "simpler is better contrast, contrast is the key"

   and , "lowest lost is best....transmission is key".

   An Abbe, now with muli-coating is almost impossible to defeat for fine detail....

    but under 50 degrees. I wish they made one with 2-layer outer coatings, though. 

  You can get great contrast "considering"

    with a widefield EP, but some look and see the proof in the galactic pudding.


Edited by MartinPond, 05 June 2020 - 08:16 AM.

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#17 alnitak22

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Posted 05 June 2020 - 09:57 AM

I'm interested in obtaining representative light transmission percentages for some of the eyepieces in my collection so I did some digging in CN and elsewhere and came up with some information. While I realize the values may not be specific to each iteration of ocular, I'm particularly interested in those above 95% and the latter is an arbitrary demarcation a CN reviewer used in his determination of values for various 1.25" eyepieces.  Of the many that he tested, I find those in my collection to make the cut:

1 UO Ortho 25mm @ 97.3%

2 UO Ortho 18mm @ 95.7%

3 BGO Otho 9mm @ 95.7%

4. Orion Ultrascopic 25mm @ 95.5%

Those in my collection for which I could find data on and below 95%:

1 ES 9mm 100 @ 91.1%

Those in my collection that I'm seeking data on:

1 Ethos 10mm

2. UO ortho 12.5mm

3 UO ortho 6mm

4. Pentax 10.5mm 65 AFOV

5 Speers Waler 10mm 

6 ES 14mm 100

7 ES 30mm 82

8 ES24mm 82

9 Paradigm/astroguider 18mm

 

PS: Generalizations: The following series all reportedly have about the same measured levels of transmission: Pentax XWs/Delos/ BGO Orthos @95% or slightly higher. 13mm @ 17mm Ethos variable findings but averaging around 93%. Nagler T6 7 &13mm @ 87%(measured by two different reviewers).

I could find one measurement of a paradigm ocular: 8mm @ 90.5%. Expect to find some variation on the specifics of the tests employed by those making the determinations.

As reported  by Markus  Ludes from data obtained with the interfometer, the Type 6 Naglers have transmission numbers in the mid 90’s.


Edited by alnitak22, 05 June 2020 - 11:57 AM.


#18 RLK1

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Posted 05 June 2020 - 10:01 AM

Do you have references? The numbers I've seen for the T6 Naglers are much higher than that, around 94%.

 

Edit:

 

I see Don posted some links, they seem consistent with what I remember for the T-6s.

 

These are Markus Ludes's numbers:

 

TV Nagler 5mm type 6 90.79 91.83 95.24 96.86 94.11 96.96 at 596 nm
TV Nagler 7mm type 6 90.37 91.34 94.27 96.33 94.69 96.55 at 610 nm

 

Jon

CN thread: Eypiece transmission

Started by ThomasM, Nov 03 2012 06:47 PM



#19 KTAZ

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Posted 05 June 2020 - 10:11 AM

As usual, Don nails it.

 

Don’t get me wrong, I love the discussion. But I am always amused by the level of analysis, calculation, and hand wringing we do (yes, that includes me) regarding optics. Let’s face it; our stuff is not based in space and our ability to see these distant objects is much more dependent on terrestrial factors and physical limitations than light transmission.

 

I had a good discussion here regarding a 40mm TV plossl. Yes, a 32MM generic gives pretty much the same FOV but with a little higher magnification. So why keep the 40mm?

 

Because it looks superior to my eye, that’s why. No calculation or lab analysis of AFOV, TFOV, or light transmission will convince me to sell it.

 

Of course, if somebody out there wants to give me a 32MM TV plossl, well, then we can have a discussion.

 

After I look through it.


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#20 payner

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Posted 05 June 2020 - 10:31 AM

I reckon the image that is presented best to one's own eyes by one's combination of equipment used is the best for that person. Simple, but seems to ring true.



#21 RLK1

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Posted 05 June 2020 - 11:03 AM

"When it comes to light throughput, they also suck. When comparing them to similar BGOs, I can easily see Rhea (Saturn's moon) with my EON 80 and the BGOs. With the Nagler type 6s, Rhea is not visible, even with averted vision.

"The transmission ot the nagler 7 and 13 mm T6 eyepieces is not top notch, I got values of 87%, almost 10% less transmission than that of Baader orthos in line with your findings.

Thomas"

CN thread: Eypiece transmission

Started by ThomasM, Nov 03 2012 06:47 PM


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#22 Starman1

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Posted 05 June 2020 - 11:11 AM

Sorry. Take such statements with a pinch of salt. For a moon to be easily visible in one eyepiece and not visible with averted vision in the other would require a 30% or larger transmission difference and that simply isn't the case.
Barring a prejudice that might be apparent in such remarks, such a difference, if actual, is likely to be due to other factors, like spot size in the eyepieces, focus differences, momentary seeing differences, light scatter, eye fatigue, etc. A few % difference simply won't make that amount of difference in the visibility of such a bright moon.
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#23 SeattleScott

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Posted 05 June 2020 - 11:21 AM

Maybe dirt on the lens?

Once I had a 9T1 Nagler with lower transmission. It took averted vision to resolve M37 while another newer 8mm resolved M37 with direct vision. So I sold the 9T1 locally and got a Meade 8.8. But I still have a 7T1 that gives similarly bright views to the 8mm so I suspect there was coatings damage with the 9T1. Or the 9T1 has more elements than the 7T1. That is the only time I have really noticed a difference in transmission.

For something to go from direct vision to not visible at all, even with averted vision, I agree with Don. Something else must be going on.

Scott

#24 RLK1

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Posted 05 June 2020 - 11:34 AM

Again, If anybody has any transmission values for the eyepieces in question in my initial post in this thread, please respond to it. ( I did see references to the 12.5mm UO Ortho so my thanks for the links relating to that one).

I understand there are other factors in play in what see can see thru an eyepiece, ie optical design, lens polish, lens configuration, optical-mechanical considerations and so forth.

I presume eyepiece manufacturers perform R&D on coatings for good reasons and with an ultimate goal of optimizing light transmission. Otherwise, they would not go through the time, effort and expense it takes to do so in the first place. With respect to the latter, I'm also skeptical of the some of the statements that you can't see the differences...



#25 alnitak22

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Posted 05 June 2020 - 11:45 AM

"When it comes to light throughput, they also suck. When comparing them to similar BGOs, I can easily see Rhea (Saturn's moon) with my EON 80 and the BGOs. With the Nagler type 6s, Rhea is not visible, even with averted vision.

"The transmission ot the nagler 7 and 13 mm T6 eyepieces is not top notch, I got values of 87%, almost 10% less transmission than that of Baader orthos in line with your findings.

Thomas"

CN thread: Eypiece transmission

Started by ThomasM, Nov 03 2012 06:47 PM

Why would you give any credence to a “review” that contains that first sentence above? Again...Ludes used info for transmission rates that was scientifically measured by a firm that actually gets paid for doing such things. The Type 6 Naglers were shown by the interfometer to have transmission rates in the high 90’s. 


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