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When Were Dielectric Coatings for Roof Prism Binoculars Introduced? (1 Viewer)

LPT

Well-known member
Does anybody know when the first dielectric coatings for roof prism binoculars were introduced and which manufacturer introduced them? I believe this has been discussed on this forum before but cannot find the link. I would think John A. would know.
 

Binocollector

Well-known member
Germany
Wiki claims it was invented in 1937 and used for multicoating first in 1939 by Schott. But I have no idea who used those glasses first. Zeiss maybe?
 

LPT

Well-known member
You are referencing anti-reflective coatings which are different than dielectric coatings. Anti-reflective coatings are to reduce light reflection and increase light transmission through air-glass optical surfaces. Dielectric coatings are to increase total internal reflection in prisms where this does not occur (e.g. in some roof prism binoculars such as Schmidt-Pechan types). Aluminum and silver coatings were used for this until, I think, sometime in the 1990’s when dielectric coatings were introduced. But exactly in what year and by which manufacturer I don’t know.
 

Binocollector

Well-known member
Germany
No, I meant dielectric coatings. That was exactly the wording of the Wiki-article. Not anti-reflective coatings.

"In 1939 at the Schott Glass company, Walter Geffcken invented the first dielectric mirrors to use multilayer coatings.[15]"

But you are right about one thing -- those were used for mirrors not prisms.
 

Binocollector

Well-known member
Germany
Hm, the only other info I found was that Zeiss developed the dielectric p-coating in 1988. But I guess you didn't mean the p-coating but the 2nd reflection surface in the SP-prism, right? Not the reflection at the roof.
 

NDhunter

Experienced observer
United States
1999, with the introduction of the Swarovski EL binoculars model.
The trade name Swarovski uses is Swarobright.
Jerry
 
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Alexander Stöhr

Well-known member
Hello,
I am very far from an expert on this topic, but I always thought, that Dielectric coating is applied on a mirror surface, that must reflect idealy 100% of the incoming light (evenly over the entire spectrum). Such a mirror (and therefore the need to coat it) is only present in SP-roof prisms, while AK-roof prisms and Porro prisms dont need this. = what LPT has already said

I thought to remember, that the P-coating mentioned by Gijs was developed to battle the effects of resolution and contrast loss, when then light is divided (and later cobined again) at the roof of any roof prism type (SP and AK)?

Is P therefore a short for Phase-correction/Phasenkorrektur? Thanks
 

Binocollector

Well-known member
Germany
Yep, p-coating is phase-correction coating. And from my (very rudimentary) understanding, the 2nd reflection point in the SP-prism is the one that lacks total reflectivity and therefore needs the "normal" coating (not p-coating) that was formerly done in aluminium then silver and later dielectric. So if I understand this correctly, the p-coating (not needed for reflectivity but just for the phase-correction I think) was done as a dielectric coating BEFORE the coating at the 2nd reflection point inside the prism was also done in dielectric (non-metallic) coating. I wonder why however since the dielectric coating itself (for mirrors) was invented far earlier, if I understand wikipedia correctly. So why it didn't occur to bino-makers to do all the coatings of the prism in dielectric coating after the dielectric p-coating was introduced is a mistery to me. But I am only an interested amateur. So I am not at all informed about the time-line of inventions when it comes to binoculars.
 

Gijs van Ginkel

Well-known member
Alexaner, post 8,
Yes P-coating is a dielectric mirror coating applied to that surface of the roof prims on which the light beam doest no enter under a perfect reflection agle . The first binocular in which these dielectric P-coatings were applied was, as far as I know, the Zeiss Dialyt 6x42 (1988), a very beautiful and fairly rare binocular nowadays.
Gijs van Ginkel
 

LPT

Well-known member
I didn’t know that that phase correction coating (“P“ coating) introduced by West German Zeiss in 1988 was a dielectric one. This is interesting, and I have learned something. So, yes it is clear that the first dielectric coating used in roof prism binoculars was the Zeiss P coating to correct phase shift caused by the split reflection from the roof edge a roof prism. But the question I intended to ask was when were dielectric coatings first applied as mirror coatings to the surfaces of prisms which lacked total internal reflection such as one of the surfaces of the Pechan prism, and now we know this was done by Swarovski in 1999. It’s odd, though, that 11 years elapsed between the introductions of Zeiss’s phase shift correction dielectric coatings and Swarovski’s total internal reflection correction dielectric mirror coatings.
 
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NDhunter

Experienced observer
United States
I just spent some time reading some older posts on BF from 2013 discussing different prism coatings.
Holger, Gijs and others offered some good discussion on the topic. Any search engine many bring those up.
Some things I gathered, that phase coatings are a totally separate thing from reflective prism coatings,
which is the subject at hand.
Phase coatings are applied to only one prism surface, to do their thing, and reflective prism coatings, which
may consist of aluminum, silver or dielectric are applied in another stage.
Dielectric prism coatings are complex, and may be applied in a vacuum chamber with maybe 30 different vapor
deposits being applied. And there is also a wide range of the quality of dielectric coatings.

These are just some of my thoughts, I am no expert, just trying to separate these things.
Jerry
 

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