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Binocular Light Transmission Chart

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Old Friday 17th May 2019, 18:16   #1
LPT
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Binocular Light Transmission Chart

I recently found this binocular light transmission chart on a Russian website: http://astro-talks.ru/forum/viewtopic.php?f=7&t=2884 . An edited Google translation (sections not pertaining to binoculars and telescopes were deleted) is attached for those who may be interested.
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File Type: xlsx Russian Light Transmission.xlsx (15.1 KB, 227 views)
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Old Friday 17th May 2019, 18:53   #2
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Thank you very much! Unfortunately no mention of methodology... but they're not far off what one sees elsewhere.

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Old Friday 17th May 2019, 23:32   #3
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Very nice and helpful! Thank's for posting that. Very interesting.
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Old Monday 20th May 2019, 01:15   #4
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Cool LPT, thanks for sharing.
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Old Wednesday 22nd May 2019, 00:36   #5
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Boy those Habicht's are good transmitter's across the whole RGB spectrum. A simple little porro!
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Old Wednesday 22nd May 2019, 06:10   #6
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Boy those Habicht's are good transmitter's across the whole RGB spectrum. A simple little porro!
Dennis
Perhaps a major part of the reason that it is a good transmitter is that it is simple. After all, a bino with no glass in it at all will transmit 100%.

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Old Wednesday 22nd May 2019, 06:41   #7
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Dennis
Perhaps a major part of the reason that it is a good transmitter is that it is simple. After all, a bino with no glass in it at all will transmit 100%.

Lee
I agree. All the porro's are generally very good transmitters, especially if they have good updated coatings on them. That is one advantage of a porro and they don't need any special HT glass to do it because they have LESS glass to absorb the light. Nice transmission chart. I wish it had more binoculars on it though.
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Old Wednesday 22nd May 2019, 06:59   #8
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I agree. All the porro's are generally very good transmitters, especially if they have good updated coatings on them. That is one advantage of a porro and they don't need any special HT glass to do it because they have LESS glass to absorb the light. Nice transmission chart. I wish it had more binoculars on it though.
Den

Don't forget our own Gijs has published transmission figures for many different binos here:
https://www.houseofoutdoor.com/verre...n-vergelijken/

Lee
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Old Wednesday 22nd May 2019, 07:10   #9
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Lee/Dennis,

Don't forget this data simply tells you about the normalised signal distribution between the 3 colour channels of a Canon D400 camera. It tells us absolutely nothing about the peak or average transmission levels.

David

Last edited by typo : Wednesday 22nd May 2019 at 07:12.
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Old Wednesday 22nd May 2019, 07:18   #10
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.... a little voice in my head wonders about uncertainties... without those a comparison is not meaningful. Of course if we are comparing apples to potatoes then comparing will be less possible.

Peter
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Old Wednesday 22nd May 2019, 07:20   #11
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Quote:
Originally Posted by LPT View Post
I recently found this binocular light transmission chart on a Russian website: http://astro-talks.ru/forum/viewtopic.php?f=7&t=2884 . An edited Google translation (sections not pertaining to binoculars and telescopes were deleted) is attached for those who may be interested.
Many thanks. The table appears to allow comparison of several models that I've been interested in over the years, including the old Nikon 8x30 and Swift Audubons.

Was there text to describe how the measurements were taken, equipment, etc.?

Ed
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Old Wednesday 22nd May 2019, 08:47   #12
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Dennis, post 7,
Your statement of the high inherent transmission of porros is not correct. We find very high transmissions for the newest Habicht porros and very low ones for older porros even as low as 50% or even less.
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Old Wednesday 22nd May 2019, 08:54   #13
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Lee/Dennis,

Don't forget this data simply tells you about the normalised signal distribution between the 3 colour channels of a Canon D400 camera. It tells us absolutely nothing about the peak or average transmission levels.

David
A timely reminder David, thank you.

Lee
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Old Wednesday 22nd May 2019, 08:55   #14
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Dennis, post 7,
Your statement of the high inherent transmission of porros is not correct. We find very high transmissions for the newest Habicht porros and very low ones for older porros even as low as 50% or even less.
Gijs van Ginkel
Gijs
Presumably those old porros had no coatings or very inefficient coatings.

Lee
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Old Wednesday 22nd May 2019, 11:53   #15
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Lee,
Even the older ones with coatings have sometimes quite a bit lower transmission.
Gijs
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Old Wednesday 22nd May 2019, 14:51   #16
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Lee,
Even the older ones with coatings have sometimes quite a bit lower transmission.
Gijs
Gijs,
"Even the older ones with coatings have sometimes quite a bit lower transmission."

What would you attribute that to? Why would the Habicht transmit better than the older porro's with coatings? Newer better coating's or glass? Thanks!

Last edited by [email protected] : Wednesday 22nd May 2019 at 18:26.
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Old Wednesday 22nd May 2019, 14:52   #17
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Den

Don't forget our own Gijs has published transmission figures for many different binos here:
https://www.houseofoutdoor.com/verre...n-vergelijken/

Lee
Thanks for that reminder, Lee. This forum is so informative and helpful! So many knowledgeable members!
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Old Wednesday 22nd May 2019, 16:05   #18
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Some old binoculars have yellowing balsam, possibly yellowing glass and haze on the glass surfaces.
In addition some of the glass was originally grey or dirty with imperfections.
The Barr and Stroud WW2 binoculars were made with best Scottish sand, which wasn't very clear and known to be a dirty grey colour.

Quite modern, probably Chinese, Bresser 15x60 binoculars that I have also have grey glass. I consider them to be only useful as paper weights or to keep the door open.

In addition old glass can devitrify and eventually become opaque.

Although old binoculars may be dismantled and cleaned, I am not convinced the dirty layers are always removed.

Some old Leitz camera lenses are notorious for becoming less transparent with age.
Different glass types behave differently.

Lead crystal vases are 24% lead and very grey. They are like this because cutting this glass is easy.

Quite many Broadhurst Clarkson telescopes and magnifying glasses have green glass when looked at sideways through the glass.
Some were made with plate glass window remains. This used to be collected after bombing raids.
They also kept six English house spiders to provide thread for their filar micrometers.

B.
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Old Wednesday 22nd May 2019, 16:39   #19
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Originally Posted by Binastro View Post
Some old binoculars have yellowing balsam, possibly yellowing glass and haze on the glass surfaces.
In addition some of the glass was originally grey or dirty with imperfections.
The Barr and Stroud WW2 binoculars were made with best Scottish sand, which wasn't very clear and known to be a dirty grey colour.

Quite modern, probably Chinese, Bresser 15x60 binoculars that I have also have grey glass. I consider them to be only useful as paper weights or to keep the door open.

In addition old glass can devitrify and eventually become opaque.

Although old binoculars may be dismantled and cleaned, I am not convinced the dirty layers are always removed.

Some old Leitz camera lenses are notorious for becoming less transparent with age.
Different glass types behave differently.

Lead crystal vases are 24% lead and very grey. They are like this because cutting this glass is easy.

Quite many Broadhurst Clarkson telescopes and magnifying glasses have green glass when looked at sideways through the glass.
Some were made with plate glass window remains. This used to be collected after bombing raids.
They also kept six English house spiders to provide thread for their filar micrometers.

B.

Thanks Binnie

Lee
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Old Wednesday 22nd May 2019, 20:25   #20
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Dennis, post 16,
I have looked in our files and between the different porros made between 1945 and 1980 by different companies (e.g. Beck, Bush, Goerz, Kern, Möller, Voigtländer, Wöhler, Wollensak, Bausch and Lomb, Leitz, Zeiss, Krombach, Minolta, Pentax, Hertel & Reuss, Nickel,, Nitschke, Swarovski , Bleeker, Oude Delft-Delft Instruments, Tento, Komz, Konica) between 1945 and 1980 quite a few had transmissions from below 50% up to 80% and all values in between.
As Binastro in his post 18 already has explained a number of factors can be the cause of it.
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Old Wednesday 22nd May 2019, 21:06   #21
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Thanks. Interesting. It sounds like glass quality can play a big part in it.
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Old Thursday 23rd May 2019, 11:15   #22
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It is not only glass quality. It is the skill of the optics manufacturer.
Some exotic glass types in the best professional lenses tarnish as soon as they are made. The glass element has to be coated as soon as it is made.
In addition, although some claim it isn't true, in these top quality lenses, every glass surface is coated including cemented surfaces. the coating material is matched to the glass type.
Also the edge blackening is matched to the glass type.

So besides the glass transmission throughout the glass varies, the surface of the glass has to be considered.
Some glass types are relatively inert, but some react to air and moisture.
Glass material varies in hardness also, some being very soft.

Fluorite crystal is another material that needs very special care.

Thorium glass from 1940 to 1978 or a bit later became brown because of radiation. The transmission of the early 1940s 7 inch f/2.5 Aero Ektar was probably about 40% by the 1970s, with a large colour shift.
This discolouration could be at least partly reversed by exposure to strong UV.
The smaller Pentax, Olympus, Canon and many other makers thorium glass lenses were less affected as the amount of glass in the lenses was smaller.
I note that there are now regulations regarding storing these lenses as regards weight and quantity, and I think that thorium is no longer allowed in lenses. (Maybe 5kg total thorium and/or 400 lenses. I may have just complied).
In addition, somewhat later lenses had a thorium coat in perhaps thermal imaging devices to reduce ghosting, but I haven't researched this. This can be more of a problem as the coating can flake off and be potentially inhaled.
Thoriated glass existing lenses also may not now be ground or worked on, again to prevent material being inhaled.
I have always queried what exposure lens workers had. As far as I know at the time there were no special precautions.
If such lenses are broken and a shard enters the skin, it must be removed.
Horace Dall had a very large optical flat that he had made to very high accuracy on his workbench. I immediately queried this because of its grey colour.
He wasn't at all bothered when I monitored it and the counter merrily clicked away. He didn't see any need to move it. I suppose at eighty years old he wasn't concerned, as he had other health issues.

B.

Last edited by Binastro : Thursday 23rd May 2019 at 15:17.
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Old Thursday 23rd May 2019, 14:07   #23
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Wow! I never knew there was much to consider with just glass. So all glass and all lenses are not the same.
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Old Thursday 23rd May 2019, 18:17   #24
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Originally Posted by elkcub View Post

Was there text to describe how the measurements were taken, equipment, etc.?

Ed
The table was taken from a thread on a Russian binocular forum and later in the thread there could be explanations of how the measurements were taken. Here is the thread: http://astro-talks.ru/forum/viewtopic.php?f=7&t=2884 . I haven't translated any of this material but it may be useful. Google Translate, by the way, seems to work exceptionally well, when translating Russian.
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Old Thursday 23rd May 2019, 18:20   #25
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Wow! I never knew there was much to consider with just glass. So all glass and all lenses are not the same.
There are many factors affecting binocular light transmission. Here are a few of the ones that I could think of.

1) The number of the binocular's air to glass surfaces. The more air to glass surfaces there are, the more reflection of light there will be. For example, if the light reflection per uncoated surface is 5% (this can vary depending on glass type and how the reflection is measured) and there are 10 air to glass surfaces (2 on the objective lens, 2 per each prism = 4, and 2 on each eyelens = 4) then light transmission would be no more than approximately 60% (i.e. 95% to the tenth power) and possibly less depending on other factors. Note that because of this binoculars with more complex optical systems (f.ex. having a 3 lens Erfle type eyepiece instead of a two lens Kellner or having air-spaced objectives) may have lower transmissions than ones with simpler systems particularly if the optical surfaces are uncoated or only single layer coated.
2) Type of optical glass. Different types of optical glass may transmit different wavelengths of light different ways which could affect levels of light transmission.
3) Absorption. Glass will absorb light, the amount of light being absorbed being dependent on the thickness, glass type and purity of the lens or prism.
4) Quality of optical glass. Optical glass is subject to manufacturing or material defects. During WW II US Army manuals classified 7 types of material defects and 20 types of manufacturing defects. At least some of these defects, I would imagine, could affect light transmission.
5) Condition of optical surfaces. This is particularly relevant to older binoculars.
6) Anti-reflective coatings. This can account for huge differences in light transmission depending on the condition of the coatings, the quality of the coatings, the number of optical surfaces coated and whether the coatings are single or multi (and if multi, how many layers).

Last edited by LPT : Friday 24th May 2019 at 13:58.
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