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Old Thursday 9th November 2017, 17:54   #1
tenex
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What was so hard about phase coatings?

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.)
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Old Thursday 9th November 2017, 20:58   #2
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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.
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Old Thursday 9th November 2017, 21:27   #3
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Quote:
Originally Posted by tenex View Post
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.
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Old Thursday 9th November 2017, 21:29   #4
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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.
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Old Thursday 9th November 2017, 21:38   #5
Gijs van Ginkel
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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.
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Old Saturday 11th November 2017, 03:21   #6
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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.
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Old Saturday 11th November 2017, 09:01   #7
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Originally Posted by etudiant View Post
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.

Bill
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