• Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.

    Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

What was so hard about phase coatings? (1 Viewer)

tenex

reality-based
Discussion of the new nostalgic Trinovid made me aware of something I've never really understood. Zeiss and Leica both laid a huge bet on roof prisms in the early 1960s, and were surely aware of the image degradation they suffered from despite their high cost. Yet it took 25 years to develop phase correction coatings that would deliver image quality comparable to much cheaper porro binos... why? What was really so hard about it? That's a rather technical question, but does anyone here know?

(Somehow the gamble worked: enough people bought them for many years anyway... I gather that means image quality really isn't paramount for many people, even those who can afford Leica/Zeiss, despite all the nitpicking of alphas that goes on in some circles.)
 
It is I think multilayer and an exacting coating, which was probably difficult and expensive to apply.

Once factories were geared up for it, it probably became cheaper and commercially viable.
 
Discussion of the new nostalgic Trinovid made me aware of something I've never really understood. Zeiss and Leica both laid a huge bet on roof prisms in the early 1960s, and were surely aware of the image degradation they suffered from despite their high cost. Yet it took 25 years to develop phase correction coatings that would deliver image quality comparable to much cheaper porro binos... why? What was really so hard about it? That's a rather technical question, but does anyone here know?

(Somehow the gamble worked: enough people bought them for many years anyway... I gather that means image quality really isn't paramount for many people, even those who can afford Leica/Zeiss, despite all the nitpicking of alphas that goes on in some circles.)

You also have to remember that there are many, many people who can't see well enough to tell the difference.
 
It may be that there was enough improvement in usability with the roofs to justify their selection.
My understanding is that roofs are relatively easy to make waterproof and much less likely to lose collimation than their porro counterparts.
However, I don't really know why that is so or even whether it is actually true.
Perhaps WJC or some other expert could shed light on the issua.
 
In 1943 a type of phase coating was suggested in the Zeiss workshop and it was described in a paper by Prof. Joos. It took until 1988 before the first binoculars with phase coatings were produced. However, many roof prism binoculars were already produced since 1897.
One must not forget that the controlled application of ultrathin layers under low pressure was necessary to apply the phase coatings and it had to be done under very well controlled conditions and, not to forget, it needed the proper choice of coating materials and that also was a completely new game in science and all that together needed some research and that takes time and it costs money.
Gijs van Ginkel
 
I just find it hard to imagine how it took 25 years to figure it out, when it must have been a high priority for research, and polarization of light had been well understood for a long time. It would be interesting to understand the technical challenge better.

I do understand the reasons (convenience etc) why people bought roof prisms anyway. I was curious to try a more compact bino myself and around 1988 (horrible timing!) I finally decided to get a Zeiss 8x30, must have been one of the very last made without phase coatings. I used it for some time; never loved the view, but it worked. Eventually I replaced it with a Leica 10x32 BN which I still have and enjoy today. A huge improvement.
 
It may be that there was enough improvement in usability with the roofs to justify their selection.
My understanding is that roofs are relatively easy to make waterproof and much less likely to lose collimation than their porro counterparts.
However, I don't really know why that is so or even whether it is actually true.
Perhaps WJC or some other expert could shed light on the issua.

Covered fairly well on pages 33-38 in Binoculars: Fallacy & Fact. The Zeiss paper by Weyraush and Dorband (1988) cover it more precisely, with excellent graphics.

Buy the book, anyway. I need the burger money. ........... Boy, I hate it when the tongue goes all the way through the cheek like that. :cat:

Bill
 
I'd be interested to know if there have been improvements in phase-coatings over the years, as there have been with anti-reflection coatings? We know that Zeiss' T* anti-reflection coatings are constantly being worked on - I wonder if similar efforts are being made with the P phase coatings to achieve objectives such as (a wild ass guess on my part) superior contrast, etc. P* is supposedly the same as P, but that was well over a decade ago...
 
P* is supposedly the same as P, but that was well over a decade ago...

Hey Patudo.
P is more than supposedly the same as P*, it is exactly the same. The asterisk was added to the P solely to give it the same format as T*: a letter, followed by an asterisk.

Lee
 
Thanks, Troubadour; now if I may be so bold, were the phase coatings used in FLs and subsequent Victorys improved from those used in the Dialyts?

Best regards
patudo
 
Thanks, Troubadour; now if I may be so bold, were the phase coatings used in FLs and subsequent Victorys improved from those used in the Dialyts?

Best regards
patudo

This is a good question and I don't know the answer. However there is one clue. Zeiss has a person whose job it is to improve the T* coatings so it is logical to guess that someone is responsible for keeping P* coatings competitive too.

Lee
 
In 1943 a type of phase coating was suggested in the Zeiss workshop and it was described in a paper by Prof. Joos.

Hi Gjis,

do you happen to have a reference for that? I only knew Paul A. Mauer: Phase compensation of total internal reflection from 1966 (https://www.osapublishing.org/josa/abstract.cfm?uri=josa-56-9-1219) and of course the 1988 article in Deutsche Optikerzeitung: A. Weyrauch, B. Dörband: P-Belag: Verbesserte Abbildung bei Ferngläsern durch phasenkorrigierte Dachprismen. In: Deutsche Optikerzeitung. Nr. 4, 1988.

Joachim
 
If you need burger money, ok, but the book is only for dummies

Yes, I know. That's why there are so many great reviews on the back from optical engineering professors, authors, and industry professionals and so many 5-star ratings from readers on Amazon.com. So, please don't waste your money. cat:

Bill

PS The "burger money" is a long-standing joke.
 
Last edited:
Joachim, post 17,
The article by prof. Joos is published in Zeiss Nachrichten from 1943, I will search for the paper in my archive and let you know when I found it.
Gijs van Ginkel
 
Hi Gjis,

do you happen to have a reference for that? I only knew Paul A. Mauer: Phase compensation of total internal reflection from 1966 (https://www.osapublishing.org/josa/abstract.cfm?uri=josa-56-9-1219) and of course the 1988 article in Deutsche Optikerzeitung: A. Weyrauch, B. Dörband: P-Belag: Verbesserte Abbildung bei Ferngläsern durch phasenkorrigierte Dachprismen. In: Deutsche Optikerzeitung. Nr. 4, 1988.

Joachim

Hi Joachim,

The original work seems to be

G. Joos: Die Bildverschlechterung durch Dachprismen und ihre Behebung. In: Zeiss Nachrichten. 4, 1943, S. 9

but I have no copy of that. What I do have is a copy of Mahan's work, just two years later. Therein he mentions Joos' paper which he came to know only after having finished his own studies:

A. I. MAHAN: Focal Plane Anomalies in Roof Prisms. In: Journal of the Optical Society of America. Vol. 35, No. 10, 1. October 1945, p. 623–635

Both, Joos and Mahan were apparently on the same track and worked it out independently, but due to the WWII troubles none of them knew about the other one's efforts. They recognized the existence of that interference, but - as far as I remember - they hadn't come up with a solution yet. It had been noted that the performance of the prism improved once the roof-faces were coated with metal layers. I can only guess that the partial polarization, which otherwise occurs during total internal reflection, did not (or: to lower extent) show up in presence of that thin (and probably rather disordered) metallic layer. Yet: Who wanted to coat such a roof-prism with another two metal layers, thus inducing additional loss of light?

Cheers,
Holger
 
Warning! This thread is more than 6 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Users who are viewing this thread

Back
Top