33 replies to this topic

[25585]

Light transmission (or whatever you call it), gets mentioned comparing eyepieces. What it matter most to you on, what more does it show you?

[CrazyPanda]

Light transmission matters when I'm observing at threshold light levels to start with - faintest galaxies, or at exit pupils that are probably too small for the task.

 

When observing the HH nebula with a 5.5nm H-Beta filter, I've progressed from 6.2mm exit pupil, to 5.7mm exit pupil, to 4.7mm exit pupil, each time trading brightness for magnification to find that optimal balance where the HH is most easily presented.

 

The extremely high transmission of the 25 TPL helps in this task. It's easy to compare against the 25mm Meade Series 3000 Plossl that has basic 30 year-old coatings. Fainter nebulosity of IC 434 can be traced out further in the TPL than the Meade. The HH seems to stand out a tiny bit more in the HH.

 

Another example - last year I was comparing the 7mm Pentax XW against the 7mm Nikon NAV-SW. The Nikon's anti-reflection coatings and transmission seem to be lower than the Pentax, and when I was looking for IC1101 (which is a threshold object for my skies), it was easier to see in the Pentax than the Nikon.

 

All that being said, these are specialized tasks. For general purpose observing, high transmission isn't that important because it doesn't change contrast. As long as the transmission difference isn't starving the eye for light, there isn't a whole lot to be gained.

[Alvin Huey]

Threshold deep sky objects, compact galaxy groups and faint details in deep sky objects.

 

Low glass count eyepieces consistently outperforms "high-glass count" eyepieces.

 

See this link (scroll all the way to the bottom) http://www.faintfuzz...ervingAids.html  Short summary of what was observed at GSSP.  The five observers included (no names) two very experienced observers and one beginner.  Then at OSP (last paragraph) was confirmed by two observers, one works with ultra high end optics and telescope systems.

 

Bottom line, there is a difference, which is why I use orthos in 80-90% of my observing in my 22" f/4 reflector.  

[PKDfan]

Light transmission (or whatever you call it), gets mentioned comparing eyepieces. What it matter most to you on, what more does it show you?

Linda is looking Really Good today Richard.

I've discovered that specific eyepiece designs promulagate certain 'enhancements' with them and in my case the moons crater rays delineation is superiour to more complex negative positive designs.

Specifically a Pløssl has revealed new detail that was lost with my T2 Nagler or a couple Morphii.

My new long Delos has shown me better M42 details that were obvious at first glance that i can't recall being so 'in your face'.

Conversely my long 20mm T2 Nagler has weak transmission numbers and Never have i see such microlevel contrasts and incredible spectrum discernments AKA star colours.


Good Question Richard !


CSS
Lance

[Jay_Reynolds_Freeman]

It certainly matters when I am observing objects near the telescope's limiting magnitude, but what also counts is what happens when the light that is not transmitted gets in the way: Depending in detail on the design and construction of the eyepiece and the quality of its coatings, some of it may end up as general glare spread across the field of view, reducing contrast on details or objects that are low-contrast in the first place. The latter issue is of particular importance when the object I am looking at is bright but has low contrast details -- e.g. planets -- or is a bright star with a faint companion, because in those cases there is a lot of non-transmitted light to end up in the wrong place.

 

Clear sky ...

[Alvin Huey]

Jay is right.

 

Thanks is why I use ZAO-II o BGO for the "low-glass count" and Delos as my "high-glass count" eyepieces.  They are well polished with excellent coatings.  Minimal to no glare through the eyepiece...

 

Long story short, use good eyepieces...

[TayM57]

I think most eyepieces tend to be closer to each other in terms of light transmission, than further apart. Transparency in the atmosphere is a more important factor to me. For instance, I can't tell the difference between top level EPs for light transmission differences. 

 

But there are a couple of EPs that stand out for particularly low light transmission to me. The 9ES120 and the UFF 30. 

[Procyon]

Will a mono go little deeper than an ortho?

[25585]

Will a mono go little deeper than an ortho?

Ball eyepiece?

[Procyon]

Ball eyepiece?

I was thinking more about TMB Monocentrics. But since you mentioned a ball eyepiece, Harry Siebert claims there is none like them.   Care to try a Planisphere? 

 

Astronomers have known for years that the best views of planets and close doubles are to be had with clear skies, a good 'scope and the proper eyepieces for the job.
For most that has meant Orthoscopics and Monocentrics. The idea is to ensure the best contrast and least scatter so critical for planetary viewing. To make this possible you must use good glass, high polish, and the fewest air/glass surfaces possible. As good as Orthos and Monocentrics are, however and they may have certain advantages,  they still have 3 or more elements within them. The Logical solution...... a spherical singlet lens. No multiple elements to reduce sharpness and contrast. On axis, these special lenses produce the sharpest images of planetary detail available anywhere....Period.

Siebert Optics is proud of the Planesphere ID family of Eyepieces. Call today to discover how Siebert Optics and Planesphere can enhance your viewing experience. Planesphere: The last word in critical viewing

 

https://www.sieberto...lanesphere.html

 

https://www.cloudyni...-ball-eyepiece/

 

 

 

 

There's also a Monocentric lineup https://www.sieberto...s.com/Mono.html

 

Edited by Procyon, 15 April 2025 - 11:31 AM.

[Highburymark]

Solar binoviewing at high powers (140x for Ha) - where transmission is crucial. But any observing when you’re trying to see faint or obscure detail.
My ‘brightest’ eyepieces: TeleVue Plossls and Zeiss W-PL.

[HellsKitchen]

Faint galaxies, both those tiny ones at the limit of the scope and my own vision, and larger low surface brightness face on spirals. 

 

Larger and/or low surface brightness nebulae such as IC434, NGC 1499, Barnards Loop, Rosette, etc.

 

This would be an interesting shootout between my 20mm XWA, 26T5 and 30mm UFF. 

Edited by HellsKitchen, 15 April 2025 - 03:29 PM.

[Jon Isaacs]

 

 

Astronomers have known for years that the best views of planets and close doubles are to be had with clear skies, a good 'scope and the proper eyepieces for the job.
For most that has meant Orthoscopics and Monocentrics. The idea is to ensure the best contrast and least scatter so critical for planetary viewing. To make this possible you must use good glass, high polish, and the fewest air/glass surfaces possible. As good as Orthos and Monocentrics are, however and they may have certain advantages,  they still have 3 or more elements within them. The Logical solution...... a spherical singlet lens. No multiple elements to reduce sharpness and contrast. On axis, these special lenses produce the sharpest images of planetary detail available anywhere....Period.

 

The factors that matter for viewing the planets and splitting close doubles:

 

- the stability of the atmosphere, the seeing.

 

- the size and quality of the telescope. 

 

- with excellent seeing and a quality scope of sufficient aperture take advantage of the seeing, the eyepiece is somewhere down the list of importance's..

 

"It is not usually made clear, that these elements, objective and eyepiece, are by no means comparable in importance. The astronomer's hopes are almost wholly tied to the size and quality of the objectve. The objective of even the smallest telescope, because of its larger dimensions, the severe optical requirements it must meet, and the difficulty of its construction, completely overshadows the eyepiece."

- from "How to Make a Telescope by Jean texereau, page 1, paragraph 2.

 

Jon

[Grayoak]

For me light transmission is most important when useing a scope that dosent transmit much light.

I am a refractor nut, there is just something special about the view through a good refractor. But I am with Jon, besides seeing of course, aperture matters. I have a couple good refractors in 5 and 6 inch apertures, I think my 5 inch is ridiculously sharp and very much refractor like views. As much as I prefer the refractor view they just dont compare with even a 10 inch dob in light transmission.

So when using a refractor light transmission is most important to me and when I want quality opitics, less glass, all the light transmission I can get out of an optical train.

[John Huntley]

When I was trying to see the Horsehead Nebula I used Tele Vue Plossl's because the published % light transmission for those is high compared with many other eyepieces (even those of simple designs). I've not seen any tests of the light transmission of the Baader Classic orthos but those seem very high as well, at least in the 10mm and 18mm varieties.

 

Of course there are a host of other factors which play an important part in what is, or isn't seen when looking for faint targets but I guess I went for the best eyepiece transmission that I could afford / find on the basis that "every little helps"   

 

I did manage to see the HH nebula a few times from my back yard. The last time was with the 24mm Panoptic which is a more complex design of course.

Edited by John Huntley, 15 April 2025 - 06:28 PM.

[Grayoak]

I haven't spent much time viewing threshold DSO, as I am partial to the solar system, but I think light transmission can be important in viewing any object in any scope.

I have seen the subtle difference in seeing the E and F stars between many element eyepieces and high end less glass eyepieces as well as the big difference between small and large apertures. This holds true when viewing cloud bands on Jupiter and other solar system objects.

It is all about trade offs. You can influence light transmission by spending more money on high end optics and polish, or by the aperture of the objective or mirror. Its always about the trade offs of money, size, weight.

I cant think of any object I wouldn't want the best light transmission when viewing. But I can think of many objects I am happy to view with what I can afford and manage.

[PJBilotta]

Light transmission, for me, is my most important measure of an eyepiece, after sharpness. Perhaps a quirk of my eye, but I can detect the slightest difference in transmission between eyepieces. It makes a world of difference to me - particularly on nebulae and fainter galaxies.

A couple of examples . . . M17, M13 or the Veil through a Delos, Morpheus or Nikon SW is superb. For me, they "glow" in these eyepieces with a kind of flourensence. Yet, I glimpse finer detail, whisps, and greater nebulousity in my 10mm XW. It's not perfect - a bit less tight at the edges and a hair less contrast. The object "pops" or "glows" more in the Morpheus or Delos, against their higher contrast backgrounds. However, more is revealed in the higher transmission of the XW (and 10.5 XL).

I've spent many a long session viewing M17 through a 10mm Delos or 9mm Morpheus, and they're certainly "wow" experiences. Bright, high contrast, and exquisitely sharp. When I pop in the 10mm XW, it's not as pristine, but a little brighter. The contrast isn't as dramatic, but what is that little wisp or tendril there? Is that the brighter sky background or real nebulousity I'm seeing? It's real.

This is why I'll likely hang onto both my 10mm Delos and XW, despite their duplication. One (the Delos) is technically perfect, with exquisite sharpness and contrast. The other (the XW) somehow reveals intricate detail and subtlety that are awe-inspiring. What a luxury to have both.

Edited by PJBilotta, 15 April 2025 - 11:30 PM.

[CrazyPanda]

The XWs are definitely bright. Those SMC coatings are exceptional. I can readily see the difference between the 7 XW and the 7 NAV-SW.

 

However, I can also see mild edge of field brightening in the XWs that I don't see in Delos or the Nikon, and I do wonder if that's some kind of contributing factor to the perception of the extra brightness in the XWs. I definitely know it's not *the* cause of the extra brightness because I can see threshold objects more easily in the XW than the NAV-SW, but the NAV-SW also has a noticeably more uniformly lit field than the XW does.

Edited by CrazyPanda, 15 April 2025 - 11:34 PM.

[John Huntley]

The XWs are definitely bright. Those SMC coatings are exceptional.....

 

 

As far as I know, XW's are the only eyepieces where the transmission (96 %) is actually stated in the specs.

 

I believe they use a special coating technique between the cemented glass surfaces as well as the glass to air junctions. Not the only manufacturer to do this I know but possibly a contributor to excellent transmission ?

[C0rs4ir_]

How is transmission defined in different eyepieces? I doubt we can really compare "transmission" statements of different companies.

That would depend on the wavelength range.

[RAKing]

Light transmission is important in everything!

 

I must use smaller scopes now, so I can use every bit of light I can collect.  But it’s especially better on the smaller, fainter comp stars during my variable star work, and face-on DSO galaxies, etc. when I am playing Star Tourist.

 

The TV Delos are very good transmitters, and I hope the new T7 Naglers are even better.

 

Cheers,

 

Ron

[Highburymark]

How is transmission defined in different eyepieces? I doubt we can really compare "transmission" statements of different companies.
That would depend on the wavelength range.

Absolutely - there’s a recent thread on CN where someone has posted transmission figures by wavelength from a German website I believe.

[CrazyPanda]

Absolutely - there’s a recent thread on CN where someone has posted transmission figures by wavelength from a German website I believe.

Transmission can not only vary by wavelength, but also over the field:

 

https://www.cloudyni...ves/?p=12277901

[j.gardavsky]

Absolutely - there’s a recent thread on CN where someone has posted transmission figures by wavelength from a German website I believe.

The transmissivity is in a recent, otherwise unrelates thread,

https://www.cloudyni...5#entry14078552

post #94 by Procyon https://www.cloudyni...eps/?p=14073894

and in the following posts,

 

JG
 

[Highburymark]

Transmission can not only vary by wavelength, but also over the field:

https://www.cloudyni...ves/?p=12277901

Interesting - thanks