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Binocular Light Transmission Chart (1 Viewer)

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.
 
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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.
 
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).
 
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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.
Gijs van Ginkel

The Zeiss Jena DF7x40, aka the Checkpoint Charlie glass, standard issue for the East German Army, is famous for its relaxed and easy view, but has only about 60% transmission. So I think there are a lot more important factors in selecting a glass than a few percent difference in the transmission ratio.
 
I agree with LPT fully in practice that an old Porroprism binocular with 10 air to glass surfaces each side has a transmission of 50%, maybe less.

But 0.95 to the tenth power is 59.8% i.e. 60%, and 0.96 to the tenth power is 66%.
According to google, as I am tired and cannot be bothered to do the calculation on paper.
So the calculated transmission is around 63% with ten air to glass surfaces, without all the other factors.

I think that some of Gij's measures were down to about 30% for very old binoculars.
 
Binastro, post 27,
Below 30% was fairly rare and we saw it in some porros from before 1900 and some later ones also.
Also old draw tube telescopes from 1800-1850 show transmission values which force you to wheep and have mercy with the sailors who used them on ships battered by high waves.
Gijs van Ginkel
 
But 0.95 to the tenth power is 59.8% i.e. 60%, and 0.96 to the tenth power is 66%.
According to google, as I am tired and cannot be bothered to do the calculation on paper.

Thank you for pointing this out. This is absolutely correct, and I have edited my post accordingly.
 
Thanks LPT.
It took me three minutes on a postnote to get 59.9% long hand, by curtailing the decimal places.
Google gave 59.8%.

I had an early 1800s Ross ship's scope, possibly wooden tube, I can't remember.
It may have been this one that I couldn't open to clean. I showed it to Horace Dall and he instantly gave it a mighty tug and pulled it apart.
I had a later Ross draw tube scope. Jim Hysom wanted it. I told him that the optics were poor but he still wanted it. He was a highly skilled optics maker, but told me later that he couldn't improve it much and indeed it had poor optics.

The Aerial telescopes from around 1675 must have had quite good transmission, perhaps 70%. But no tube at all. There wouldn't be light pollution then. The objective was mounted on a tree or pole and the eyepiece possibly two element hand held or on a stand.
Up to 600ft long. Now that is dedication. They probably needed an assistant not afraid of heights. Although I think that some used ropes to make adjustments.
The Huyghens ones were up to 8.5 inch objective diameter and 210ft long.
Apparently Cassini found two Saturn moons with such a scope.
I have tried about a 6ft aerial scope, but 600ft! Wow.

B.
 
Binastro and Gijs. Why in your opinions do the Habicht's have such high transmission if not all porro's have high transmission?
 
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Dennis, post 31,
That is a combination of optical glass quality, amount of optical surfaces, coating quality and distance light has to travel through the optical glass components.
Gijs van Ginkel
 
Dennis, post 31,
That is a combination of optical glass quality, amount of optical surfaces, coating quality and distance light has to travel through the optical glass components.
Gijs van Ginkel
Thanks. So they must have really high quality glass, a lower number of optical surfaces, excellent coatings and a short light path. Good to know. So the Habicht's transmit better than say the Nikon SE and EII because of better glass quality, number of optical surfaces, better coating quality and a shorter light path?
 
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Frankly, I think that Swarovski had to maximise transmission, by using high transmission glass and special coatings to sell these.
They seem to behave very poorly as regards flare, which is why I haven't even bothered.
There is little point in 96% transmission if I can't see anything because of flare.
 
There is quite a bit of flare in the Habicht 8x30 W but it can be controlled with lens hoods, the Habicht 10x40 W which I just bought is excellent for flare and I have been comparing it to my SV 10x32 and I think it might be better overall with the 3D image and the Habicht 7x42 W if you can tolerate the narrow FOV has no flare. The Habicht's are amazingly bright and stunningly sharp on-axis. They are quite the binocular if you can tolerate the smallish eye cups and tighter focuser. I cup my hands around the eye cups to deal with the smaller eye cups and adjust the eye relief. The focuser breaks in and is easier with time and at least it has no backlash like some roof's I have tried.
 
Thanks. So they must have really high quality glass, a lower number of optical surfaces, excellent coatings and a short light path. Good to know. So the Habicht's transmit better than say the Nikon SE and EII because of better glass quality, number of optical surfaces, better coating quality and a shorter light path?

I'd say the main factor is the Habicht's multi-coatings i.e. their quality including the number of layers of multi-coating. Also, how many lenses are there in the Habicht Porro I models' eyepieces? Offhand, I think they have relatively narrow fields of view compared to other Porros which may indicate a non-wide angle type two lens eyepiece while the other Porros like the EII and SE may have a 3 lens eyepiece. If I'm correct about this, # of air to glass surfaces would also be a main factor. Would be interesting to see schematics of some of the eyepiece builds of the Habichts, SE's and EII's.
 
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Dennis, in addition to my response in post 32: your question is text book stuff so to speak.
Optical gass absorps light and the longer the pathlenght through the glass the more light is lost. Fortunately nowadays there are high transmission glass types, which reduce light losses by that process quite a bit. If Swarovski uses as few glass components as possible in the Habicht that cause of light losses is lower. Higher light losses occcur due to reflection on glass surfaces and high quality coatings reduce these losses to a very large extent and if the number of reflecting surfaces is also low one again prevent light loss. Swarovski but also the other binocular makers have generally excellent coating facilities, but every company has its own secrets with regard to their coatings and their efficiency/quality.
Gijs van Ginkel
 
I'd say the main factor is the Habicht's multi-coatings i.e. their quality including the number of layers of multi-coating. Also, how many lenses are there in the Habicht Porro I models' eyepieces? Offhand, I think they have relatively narrow fields of view compared to other Porros which may indicate a non-wide angle type two lens eyepiece while the other Porros like the EII and SE may have a 3 lens eyepiece. If I'm correct about this, # of air to glass surfaces would also be a main factor. Would be interesting to see schematics of some of the eyepiece builds of the Habichts, SE's and EII's.
It looks like their is quite a bit of glass in the Habicht's. From Scopeviews Habicht 10x40 Review. http://scopeviews.co.uk/Swaro10x40Habicht.htm

"Optics – Eyepieces

The eyepieces are physically tiny compared to many modern binos’, about the diameter of the eye lenses on a pair of ELs. You might think that means they are just basic Kellners, but cutaways of the Habichts show a 6-element design tying in with the tech-sheet’s claim of 10 optical elements per side (two for the objectives, two prisms and six in the eyepiece). However, note that the identical-looking 7x42mm Habichts do have basic eyepieces, accounting for their very narrow FOV. In the case of these 10x40 Habichts, those multi-element eyepieces give a field of about 60° apparent and 6.5° true, which is well up to modern standards, though narrower than Nikon’s otherwise quite similar 10x35 EII porros."
 
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The very same 6 element, 3 group Erfle (patented in 1923) is used in both the 8x30 and 10x40 Habichts. There are 12 glass to air surfaces total. The Nikon SE and EII have six element eyepieces, but in a more modern 4 group design, so 14 surfaces total. The Swarovski Porros with the fewest surfaces were the 7x42, 7x50 and 8x56 SLs with 3 element, 2 group Konig eyepieces and cemented prisms, only 8 surfaces.
 
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The very same 6 element, 3 group Erfle (patented in 1923) is used in both the 8x30 and 10x40 Habichts. There are 12 glass to air surfaces total. The Nikon SE and EII have six element eyepieces, but in a more modern 4 group design, so 14 surfaces total. The Swarovski Porros with the fewest surfaces were the 7x42, 7x50 and 8x56 SLs with 3 element, 2 group Konig eyepieces and cemented prisms, only 8 surfaces.
Henry, thanks for the explanation! If their are 12 glass to air surfaces in the Habicht and Scopeviews says they have the same glass as the Swarovski EL's and probably the same coatings why do the Habicht's still have 5% better transmission than the EL's? Does it have something to do with the more efficient fully reflective porro prisms of the Habicht versus the less efficient phase corrected roof prisms of the EL?
 
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