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

Joachim, post 17 and Holger, post 20,
The reference given by Holger of the article by Prof. Joos is correct: Zeiss Nachrichten 4, heft 9, 1943, pages 221-227.
On page 221 Joos writes about the correction for the phase shift by roof prisms: "Die von Herrn Werkmeister Wendland gemachte Beobachtung, dass durch Versilberung der Flächen eine wesentliche Besserung zu erziehlen ist, gab den Anlass, der Ursache dieser Bildverschlecterung nachzugehen,....
After discussion about the cause of the phase shift on pages 221-226, Joos writes on page 227:
"Nachdem so die Ursache der merkwürdigen Bildverschlechterung gefunden ist, muss sich auch ein Weg zur Beseitigung angeben lassen. Dieser ist durch den Ersatz der Totalrefexion durch metallische Reflexion vorgezeichnet (DRP. angemeldet). Aus den Werten der optischen Konstanten der Metalle liesse sich, allerdings mit erheblichen Rechenaufwand, das für jedes Prisma güstigste Metall ermitteln. Einfacher ist aber bei der geringen Anzahl der in Betracht kommenden Metall der Weg des Probierens. Auf diese Art wurde gefunden, dass bei den vorkommenden Prismen eine Belegung der Dachflächen mit Aluminium die Störungen so gut wie restlos beseitigt. Allerdings muss wegen der zweimalige Reflexion ein Lichtverlust von etwa 25% in Kauf genommen werden".
So the cause of the phenomenon is clear and so is a solution, but it would take some time before the instrumentation and most suited materials and measuring techiques were available to deposit ultrathin layers with hardly light losses could be applied obviously.
Gijs van Ginkel

Thanks to Gijs and Holger for casting a light on this historical development.

Lee

Gijs van Ginkel said:

Joachim, post 17 and Holger, post 20,
The reference given by Holger of the article by Prof. Joos is correct: Zeiss Nachrichten 4, heft 9, 1943, pages 221-227.
..... Auf diese Art wurde gefunden, dass bei den vorkommenden Prismen eine Belegung der Dachflächen mit Aluminium die Störungen so gut wie restlos beseitigt. Allerdings muss wegen der zweimalige Reflexion ein Lichtverlust von etwa 25% in Kauf genommen werden".
So the cause of the phenomenon is clear and so is a solution...
Gijs van Ginkel

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Excellent research!
One wonders whether a more careful metal deposition possible with todays techniques could avoid that 25% light loss. It might be considerably simpler to implement.

Troubador said:

Thanks to Gijs and Holger for casting a light on this historical development.

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Thanks indeed to Gijs and Holger - so the effect was known and understood but the means to properly mitigate it were not yet known.

Joachim

Gijs van Ginkel said:

The reference given by Holger of the article by Prof. Joos is correct: Zeiss Nachrichten 4, heft 9, 1943, pages 221-227.
On page 221 Joos writes about the correction for the phase shift by roof prisms: "Die von Herrn Werkmeister Wendland gemachte Beobachtung, dass durch Versilberung der Flächen eine wesentliche Besserung zu erziehlen ist, gab den Anlass, der Ursache dieser Bildverschlecterung nachzugehen,....
After discussion about the cause of the phase shift on pages 221-226, Joos writes on page 227:
"Nachdem so die Ursache der merkwürdigen Bildverschlechterung gefunden ist, muss sich auch ein Weg zur Beseitigung angeben lassen. Dieser ist durch den Ersatz der Totalrefexion durch metallische Reflexion vorgezeichnet (DRP. angemeldet). Aus den Werten der optischen Konstanten der Metalle liesse sich, allerdings mit erheblichen Rechenaufwand, das für jedes Prisma güstigste Metall ermitteln. Einfacher ist aber bei der geringen Anzahl der in Betracht kommenden Metall der Weg des Probierens. Auf diese Art wurde gefunden, dass bei den vorkommenden Prismen eine Belegung der Dachflächen mit Aluminium die Störungen so gut wie restlos beseitigt. Allerdings muss wegen der zweimalige Reflexion ein Lichtverlust von etwa 25% in Kauf genommen werden".
So the cause of the phenomenon is clear and so is a solution, but it would take some time before the instrumentation and most suited materials and measuring techiques were available to deposit ultrathin layers with hardly light losses could be applied obviously.

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Very interesting stuff! Maybe Zeiss actually used the technique described here, albeit in a scope, not in binoculars, in the Zeiss Dialyt 40x60 (http://www.monocular.info/cz_dial40x60.htm).

The Zeiss 40x60 had an AK prism and came onto the market in 1977, well before phase coatings as we know them arrived in 1988. The optical quality was very good indeed, on a par with scopes using porro prisms like the Zeiss Jena Asiola (http://www.monocular.info/cz_asiola.htm) or the Kowa TS 1. It was also clearly better than its Hensoldt predecessor (http://www.monocular.info/dialyt40x60.htm) or its smaller brother, the Hensoldt 25x56 (http://www.monocular.info/dialyt25x56.htm), so much so that the difference couldn't be explained by probably somewhat more modern coatings. In fact, I used the small Hensoldt for travelling for quite a few years and asked Zeiss if they could "upgrade" it which they declined to do, so I sold it.

A friend of mine had a Zeiss 40x60 for quite a few years, and I remember we both wondered how Zeiss acchieved such optical quality with an AK prism before phase coatings arrived. Maybe that Gijs' posting explains what we saw.

Hermann

etudiant said:

One wonders whether a more careful metal deposition possible with todays techniques could avoid that 25% light loss. It might be considerably simpler to implement.

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Did they in fact manage to do that by 1988, or was it necessary to find a different sort of material that would work instead of metal? (Does every manufacturer use the same material now, or is it proprietary?)

So this was the challenge: a coating of a suitable material to correct the phase, yet also transparent enough to give high transmission. Thanks Holger and Gijs for that.

Gijs van Ginkel said:

Joachim, post 17 and Holger, post 20,
The reference given by Holger of the article by Prof. Joos is correct: Zeiss Nachrichten 4, heft 9, 1943, pages 221-227.
On page 221 Joos writes about the correction for the phase shift by roof prisms: "Die von Herrn Werkmeister Wendland gemachte Beobachtung, dass durch Versilberung der Flächen eine wesentliche Besserung zu erziehlen ist, gab den Anlass, der Ursache dieser Bildverschlecterung nachzugehen,....
After discussion about the cause of the phase shift on pages 221-226, Joos writes on page 227:
"Nachdem so die Ursache der merkwürdigen Bildverschlechterung gefunden ist, muss sich auch ein Weg zur Beseitigung angeben lassen. Dieser ist durch den Ersatz der Totalrefexion durch metallische Reflexion vorgezeichnet (DRP. angemeldet). Aus den Werten der optischen Konstanten der Metalle liesse sich, allerdings mit erheblichen Rechenaufwand, das für jedes Prisma güstigste Metall ermitteln. Einfacher ist aber bei der geringen Anzahl der in Betracht kommenden Metall der Weg des Probierens. Auf diese Art wurde gefunden, dass bei den vorkommenden Prismen eine Belegung der Dachflächen mit Aluminium die Störungen so gut wie restlos beseitigt. Allerdings muss wegen der zweimalige Reflexion ein Lichtverlust von etwa 25% in Kauf genommen werden".
So the cause of the phenomenon is clear and so is a solution, but it would take some time before the instrumentation and most suited materials and measuring techiques were available to deposit ultrathin layers with hardly light losses could be applied obviously.
Gijs van Ginkel

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Dear Gijs,

Thanks a lot, so they found that an Al coating would almost eliminate that problem. P-coatings, however, as introduced by Zeiss in 1988, have always been dielectric. Obviously, the price of having 2 (Abbe König) or even 3 Al coated surfaces would have been too high to take, in terms of transmission losses. Most interesting seems another fact: The disadvantages of roof-prism binoculars, with their loss of resolution, have not prevented their success on the consumer market, on which they effectively eliminated the Porro binocular already prior to the introduction of P-coatings.

Cheers,
Holger

PIER PAOLO said:

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

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It always makes sense to target the largest market. :brains:

Ed

elkcub said:

It always makes sense to target the largest market. :brains:

Ed

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The largest market of people who care about buying binoculars? And don't know doodly? Oh dear.

Holger Merlitz said:

Most interesting seems another fact: The disadvantages of roof-prism binoculars, with their loss of resolution, have not prevented their success on the consumer market, on which they effectively eliminated the Porro binocular already prior to the introduction of P-coatings.

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Yes, that's exactly the thought I began this thread with: image quality is not paramount to most people. They will sacrifice it (somewhat) to get a smaller glass that's easier to carry around, or less noticeable to others, or maybe even less military-looking? I used a Dialyt 8x30 myself for a while that lacked P-coatings, and the view seemed quite decent unless compared with a Porro model.

tenex said:

Yes, that's exactly the thought I began this thread with: image quality is not paramount to most people. They will sacrifice it (somewhat) to get a smaller glass that's easier to carry around, or less noticeable to others, or maybe even less military-looking? I used a Dialyt 8x30 myself for a while that lacked P-coatings, and the view seemed quite decent unless compared with a Porro model.

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I was around in the days before p-coating. My memory is that very few people realized they were sacrificing any optical quality at all when they bought a high priced Leitz or Zeiss roof. Magazine reviewers used the same superlatives to describe the image quality of roof prism binoculars then as now.

"Looking through these binoculars is like having a little light bulb illuminate a perfect image". That's a quote describing the #1 rated Zeiss 7x42 Dialyt from a Cornell Lab "Living Bird Quarterly" group test of binoculars in 1988. It wasn't that the testers lacked Porros for comparison. That test contained some noteworthy Porros, like the Swift Audubon and the CZJ Octarem, which appear well down on the list below a number of forgettable roofs. The testers "saw" what they expected to see, based on price, brand prestige and probably group think.

One has to be a brave reviewer to go against the accepted verdict of experts or indeed majority opinion or the known critics of everything.

Often it is better to keep quiet and make no comment.

Henri,post 32,
In 1988 probably hardly anybody had heard of phase coating, since the first binocular with it was to my knowledge the 6x42 Dialyt from Zeiss, so it is not so strange that the reviewers were very enthousiastic about the 7x42 Dialyts, actually when I take the Leitz Trinovid 10x40B from 1982 it was quite good and I have used it with great pleasure, despite the presence of different porros from different companies.
I once bought an 8x56 Hensoldt Dialyt long before the phase coating area and it functioned very well. Of course with todays knowledge one can do better, but that is life.
Gijs van Ginkel

henry link said:

I was around in the days before p-coating. My memory is that very few people realized they were sacrificing any optical quality at all when they bought a high priced Leitz or Zeiss roof. Magazine reviewers used the same superlatives to describe the image quality of roof prism binoculars then as now.

"Looking through these binoculars is like having a little light bulb illuminate a perfect image". That's a quote describing the #1 rated Zeiss 7x42 Dialyt from a Cornell Lab "Living Bird Quarterly" group test of binoculars in 1988. It wasn't that the testers lacked Porros for comparison. That test contained some noteworthy Porros, like the Swift Audubon and the CZJ Octarem, which appear well down on the list below a number of forgettable roofs. The testers "saw" what they expected to see, based on price, brand prestige and probably group think.

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I agree with Henry here. My first real life WOW moment with a binocular was as a Biology student in 1970 with a Leitz Trinovid.

There is a 7x35 porro thread going where the quality of the image of the Bushnell Rangmaster is extolled. As an owner of two Rangemasters I agree with that opinion. Put the Rangemaster alongside a modern glass or even a Baush & Lomb Zephyr and the viewer is in for a surprise.

We all tend to get too locked into believing the objective results from the design table and the optical tests will translate into significant subjective field observable differences. No the oldies are not on the same level as the current crop, but the differences may well be far less than some expect.

I was very impressed with the image through my Nikon 8x40 DCF Classic Eagle roofs, which lack phase coatings. They were the first bins that I owned (and thus that I really got to know through extended use) that had decent eye-relief for glasses, a big sweet spot (due to flat field correction), smooth easy precise focus operation, and fit my hands well. Those qualities made that bin so easy to look through and use to find birds, and so superior overall to any of the $45 porros that I'd borrowed or used from my high school biology teacher, that I didn't find them lacking. In fact, I couldn't imagine how a bin could be any better. And on one occasion, when I compared them to a Zeiss (perhaps from the mid 1980s), I immediately found the Zeiss inferior due to its relatively poor off-axis performance.

It was only later, when I bought a good porro to function as a compact travel bin (the B&L 7x26 Custom Compact), that I discovered, to my surprise, that the little compact appeared to be optically superior in some ways to my unbeatable Nikon Classic Eagles. It appeared to have better contrast, to show more detail in shadows and backlit situations, and to somehow seem sharper and brighter, despite being so much smaller. The same differences were obvious when I compared my Nikon to a Swift 8x42 Ultralite. Around that time (~1991?), B&L started aggressively advertising their use of p-coatings on their newly updated Elite bins, and describing the inferior qualities of roofs without them. Egads! Their descriptions seemed to capture what I noticed seemed lacking about my Nikon Classic Eagle compared to good porros. I couldn't afford the B&L Elite, but I kept reading about bins and started paying more attention to binocular design and tech. I noticed that Zeiss and Leica then started advertising that they'd already been using phase coatings since the late 1980s! A couple years later, when I finally had a bit of money, I purchased the Zeiss 7x42 BGATP, which was super bright and contrasty compared to my Nikons (which I then "retired"). But I missed the flat field of the Nikon. I didn't get all my favorite qualities of those two bins consolidated into one until the Swarovski 8.5x42 EL Swarovision was released.

--AP

I suppose you could argue that consumer demand for roofs drove the development of phase coatings as well.

My experience with decent binos didn't begin until 1999 with the phase coated Pentax DCF WP 8x42. Before that just a Kmart porro. Widefield and about zero eye relief. I think the move to longer eye relief was a real game changer as well. With my astigmatism I simply need glasses, hence eye relief. Without it, forget it. I'd rather just try to get closer. 8-P

When we first had binos (Swift porros) they took up so much luggage space on our motorcycle (see below) that it was a real problem. Plus they weren't waterproof and kept fogging. We were so glad to get compact and waterproof roofs.

Lee

Hi Lee.
I see that your motorcycle previously belonged to Arthur C. Clarke.

I used only Porroprisms from about 1960 t0 2000.
I don't think I used roof prisms much till well after 2000, and use about half and half now.
For me the FOVs of most roof prism binoculars is just miserly.

My first roofs were Nikon Venturer LX 10X42.

Troubador said:

When we first had binos (Swift porros) they took up so much luggage space on our motorcycle (see below) that it was a real problem. Plus they weren't waterproof and kept fogging. We were so glad to get compact and waterproof roofs.

Lee

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Much more importantly: that bike!