"Phase Compensation of Internal Reflection" by Paul Mauer, J. Opt. Soc. Am. 56, 1219 (1 Viewer)

"Phase Compensation of Internal Reflection" by Paul Mauer, J. Opt. Soc. Am. 56, 1219

FWIW

The original paper for practical phase-correction in prisms (and other reflective optical devices) is

"Phase Compensation of Internal Reflection" by Paul Mauer, J. Opt. Soc. Am. 56, 1219 (1966).

in which Mauer, who was working for Eastman Kodak Company Research Laboratories, used a three layer coating to compensate the phase lag between incident llight and the reflected s- and p-polarized components from a corner cube reflector.

The original need for phase correction in roof prisms was noted in the early 1940s by a Dutch physicist (I think his name was Gill but I can't find the reference.)

Of course I don't have a copy of it but at least I could look up the paper at the UW.

You can see the abstract here (and buy a copy of the paper too!)

http://www.opticsinfobase.org/abstract.cfm?id=53137

Abstract: Symmetrical three-layer thin-film combinations are described which eliminate the difference in phase shift on reflection, of the S and P components of light incident beyond the critical angle. These three-layer combinations have low Herpin equivalent indices, but high enough material indices so that the critical angle is not exceeded until the final interface. Phase compensation is achieved at greater angles of incidence than those which can be compensated by single-layer films.

If you are not familiar with terms like s-polarizaed and p-polarized light this might help

http://en.wikipedia.org/wiki/Brewster's_angle

and for more detail

http://en.wikipedia.org/wiki/Fresnel_equations

Just trying to understand how the optics actually work!

Even from these rather simplified presentations it becomes clear that since there are an infinite number of variations in the refractive index of any medium (ie. glass) depending on the frequency of the light reflecting or refracting with it interactively, then all phase compensation coatings used in roof prisms are only rough approximations. Even if the number of approximations is increased to 60 or 100 or 1000 approximations across the frequency bandpass of light passing through the objective lens of an optical device, the phase corrections for the s and p light polarization problem is at best an approximation and would have to create more visual distortion that a porro prism system using surfaces exactly perpendicular to the lightpath direction.

Since all other factors are equal with porro prisms and roof prisms (ie. the cone shaped nature of the light beam accumulated and bent to reach the prisms, coatings for anti-reflection, fineness of polishing, quality of glass, eyepiece design etc.) ANY porro prism binocular made with the same materials and care as a similar roof prism binocular has to have better optical performance, because of zero phase distortion vs some phase distortion in any roofer made. Or am I misunderstanding Brewster and Fresnel?

There are places like Russia where the stampede to make and sell roof prism binoculars is much reduced because sophisticated purchasers can see that AT ANY Price, the porro prism model of an 8x42 for example, will outperform the roof prism version. It wasn't that difficult for Nikon to make their SE series (or Fujinon with the FMT series) as the easy choice for "Best visually" at each magnification level. If Pentax decided to make an ED version of the 7x50 DCF II WP they would likely be in this upper stratosphere optically as well, and they would be making a center focus, waterproof binocular with aspherical eyepieces that would likely be better than every 7x50 roof prism binocular in any comparable way.

I'm not sure why Zeiss doesn't make a waterproof internal focus version of the 7x50 Marine (anything Pentax can make I'm sure Zeiss can make), or why Swaro doesn't update their Habicht line, including models with ED or flourite lenses and high end coatings. Leica is committed to roofers at all costs, so that explains that and Minox doesn't want their expensive bins (now all roofers) with aspherical lenses to be compared to Nikon, Olympus or Pentax porros with aspherical lenses should Minox enter the porro market with a serious high end product. But until some company comes up with an infinite number of phase correction coatings for their roofer, it won't be as good as the porro they could have made with the same eyepieces and objectives.

ksbird/foxranch said:

Even from these rather simplified presentations it becomes clear that since there are an infinite number of variations in the refractive index of any medium (ie. glass) depending on the frequency of the light reflecting or refracting with it interactively, then all phase compensation coatings used in roof prisms are only rough approximations. Even if the number of approximations is increased to 60 or 100 or 1000 approximations across the frequency bandpass of light passing through the objective lens of an optical device, the phase corrections for the s and p light polarization problem is at best an approximation and would have to create more visual distortion that a porro prism system using surfaces exactly perpendicular to the lightpath direction.

Click to expand...

you've got to make a distinction between principle basic physics and practical engineering.
What you are saying about phase shift applies for other forms of optical abberations as well, for example for the chromatic abberation due to dispersion that you get in ANY TYPE of lens, i.e. also in the porro design. In the real world of technical physics it is sufficient to correct such an abberation for the three principle "colors" for which the three types of colour-sensitive receptor cells of the eye are sensitive. If it is done you'll get what is called an apochromatic correction which is universally regarded as a "colour-perfect" image. The principle holds true for phase correction, etc.

ksbird/foxranch said:

I'm not sure why Zeiss doesn't make a waterproof internal focus version of the 7x50 Marine (anything Pentax can make I'm sure Zeiss can make), or why Swaro doesn't update their Habicht line, including models with ED or flourite lenses and high end coatings.

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How do you know Swarovski is not using extra-low dispersion glass in the Habichts?
And what do you mean by high end coatings? According to the brochure these instruments have the same coatings as the roof prism models (except for the prism coatings).

Where can we get access to all these company secrets?

Curious,
T

I guess I am unaware of the basis for the reference to company secrets in the post by ThoLa. I don't keep up with Swaro products, but a few of the other posters to this forum have commented that the Habicht series porros do not use the same coatings as the most current Swaro roofers.

The argument ThoLa makes about other forms of distortions is covered where I say in my previous post that

"Since all other factors are equal with porro prisms and roof prisms (ie. the cone shaped nature of the light beam accumulated and bent to reach the prisms, coatings for anti-reflection, fineness of polishing, quality of glass, eyepiece design etc.) ANY porro prism binocular made with the same materials and care as a similar roof prism binocular has to have better optical performance, because of zero phase distortion vs some phase distortion in any roofer made. Or am I misunderstanding Brewster and Fresnel?"

Roofers have the same chromatic distortions etc. that porros have in all respects, and in addition roofers have an additional distortion that porros can't have, roof prism caused s & p phase distortion.

Having worked 9 years as a trainer for Nikon and Mamiya camera products I can tell you that you are incorrect in your belief that simply correcting the phase for three color peaks in the wide color spectrum bandwidth will somehow correct for the infinitely variable amount of phase distortion created by an infinitely variable number of color frequencies creating an infinitely variable number of out of phase s & p waves due to the refractive index of most materials like glass having a variable index of refraction for every color frequency there is. On the product engineering side we have Zeiss touting the use of 60 layers of phase coating on their roof prisms which allows them to space out the frequencies that they phase correct for, all along the wide color spectrum from violet to infrared.

But since color films never had more than 4 color response materials, film making companies were always explaining that the recreated color images were always approximations (which is why the colors rejected by the multicoatings on one brand of camera lens could cause the color balance of the image produced to vary slightly from the color balance of the image produced by a difference camera lens (even by the same company) if it used different multicoatings). Approximation of the original image with some added phase distortion still remaining is about all phase correcting coatings do. They are producing REDUCED phase distortion in a few color frequencies in hopes of a better approximation of the original image by somewhat reducing the s & p color distortion caused by roof prisms themselves.

The difference between the distortions in color fidelity caused by film (basically being non-linear in their response to various light frequencies) and roof prisms in binoculars (having added phase distortions) is that film produces more or less of a certain color in the original image, while roof prisms add phase distortions that reduce sharpness. With better phase correction approximations (like the 60 layer Zeiss phase correction roof prism coatings) you get a better Approximation of the original image, and with fewer phase correction coatings you get a rougher approximation of the original image. But with porro prism binoculars (all other parts of the light-throughpass system being the same) you don't get any phase distortions because these phase distortions are caused by a component (roof prisms) that porro prism binoculars don't use.

I don't believe in purple cows,
I am not of that schism.
But I would rather be a purple cow
than a roof prism.

ksbird/foxranch said:

I guess I am unaware of the basis for the reference to company secrets in the post by ThoLa. I don't keep up with Swaro products, ....

Click to expand...

In which case categorial statements about inferior coatings become as daring as skating on a frozen lake in late spring, don't they?

ksbird/foxranch said:

The argument ThoLa makes about other forms of distortions is covered where I say in my previous post that

Roofers have the same chromatic distortions etc. that porros have in all respects, and in addition roofers have an additional distortion that porros can't have, roof prism caused s & p phase distortion.

Click to expand...

Your criticism of the phase shift problem (distorsion is a distinct form of optical abberation) is appreciated.
Alone, it has been technically solved.
If you are not inclined to pay for this extra engineering effort is up to you, of course.

Irrespective of this, your "approximation argument" is true for any kind of lens abberation (let's be generous and regards prisms als "lenses" for the sake of the argument) !
My intention was to point out this fact because phase shift at/in roof prisms gets what may be a slightly larger than proportional attention. It is well known to all binocularists. Some pay for compensation coatings, some don't and use Porros only.
End of the story, isn't it?

Phase shift of light waves dashing through a roof prism is but one of many abberations that need to be taken into consideration. In most binoculars (roof + porro!) other abberations are much more prominent and in my view need more attention by engineers right now (distortion for example).

For phase shift there is a satisfying, albeit costly solution.

Regards,
Tom

In an effort to reduce large portions of my post being ignored to take what I say out of context here is what I am saying:

Assuming that the objective lenses, eyepieces, internal reflection reduction and air-glass surface multicoatings are the same, roof prisms can NEVER produce an image as clear and sharp as porros that are assembled equally as well, no matter how many layers of s and p phase correction coatings are used on a roofer to partially reduce the "softening" of the image caused by the out-of-phase-light phenomena (because s and p out-of-phase light softening in a roof prism design can NEVER be fully eliminated, it can only be approximately reduced, no matter how expensive the roof prism binocular is).

Other people posting to this forum have commented that Swarovski has NOT updated the multicoatings on their Habicht models to be the equal of their current roofers.

If anyone wants the best images possible in an 8x or 10xx binocular, the Nikon SE porros and the Fuji FMTseries porros seem to be rated #1 by all the experts, and the impossibility of being able to reduce ALL the softening effects caused by roof prism s and p phase distortion is likely why. I fail to understand why anyone would ignore the important portions of a post to take things out of context so grossly, unless it is because they don't understand what phenomena is being described.

It is a lucky binocularist who owns the latest alpha-roof going, believes his bino's optics to be the world's finest, and is happy as a clam. I do not wish upon him the the misfortune of looking through a large military style porro. After the Leica and the Swaro, looking through my 7x50 Fujinon FMT-SX just ain't no fun. The view is overwhelming. The awesome 50-ounce king sized individual focus encumbrance twists the knife in the wound. Such is enlightenment.

I just have to try to get over it, love roofs for what they are, and be awed at the science needed, and implemented, to make them as good as they are. A fine rugged binocular that is fun to use and tolerable to tote around, now that really is something! Unfortunately, my Fujinon gets used only for astronomy, and as an occasional daytime optical curiosity/heartbreaker/sanity check.
Ron

RonH, I agree that the Fujinon 7x50 (and worse yet the 10x70) are extremely heavy and so astronomical retailers sell binocular holders with large counterweights balancing them for reasonable astronomical use in a chaise lounge. But the 6x30 Fujinon FMTRs and the 8x30s are also razor sharp and their weight is manageable, If lower weight is needed for the absolute finest daytime views possible, then I guess the Nikon SEs are the only way to go. At half the price of the Zeiss FLs or Swaro SLC roofers, the Nikon SEs give obviously better images.

A couple of years ago a salesperson working for the nearby Cabelas took his Swaro 10x50 SLC porros to a demo of the new (then) Swaro SLC 10x50 roofer. The porro Swaro was so obviously optically superior that a little bit of heated discussion took place between the Cabela's staff and the Swaro rep team. Comments included

CabStaff "How can we be expected to sell a roof prim Swaro for the same money as the porro if the view through the binocular isn't as good?"

Reply - "Tell the customer it's lighter in weight"

CabStaff "Then why not make the 10x50 porro lighter?"

Reply - "That's a marketing department decision?"

CabStaff "Why is a poorer image more important than lighter weight, when both of these binoculars are pretty heavy anyway, and Zeiss makes a lightweight fiber porro body binocular?" (not sure what model he referred to)

Eventually the CabStaff supervisor ended the "discussion" and told the staff later that Cabelas was working with Leupold to eventually have waterproof porros with center focus and lighter weight, some possibly with ED objectives for half the price of the Swaro roofers, and so no one would need the Swaro 10x50 SLC porro any more.

For some reason the US market has been conditioned (conned) to believe that just because a product is more expensive it HAS to be better (even if it isn't). That is probably why people hang onto their Swift 8.5x ED lens porros. At a recent Japanese star party there were many questions from visitors to Nikon reps asking why the Nikon SEs weren't made in waterproof versions the way the Action Extremes are made. The Pentax reps got similar questions about why their CF waterproof porros didn't utilize the Pentax ED objective lenses to go with their aspherical eyepieces and the answers came back that this would make the roofers by both Nikon and Pentax look so obviously bad that there would be lots of "market confusion".

Japanese companies try to avoid market confusion as much as possible because then they can't sell as many super-expensive roof prism binoculars with slightly more convenient formats against their own brand of high end porro prism binoculars with much better optical images, and at half the price. That's probably why Swaro discontinued the porro 10x50 SLC.

ksbird it's all a matter of tolerances.

And the fact is you can tweak a phase compensating layer just the same way as you design any multilayer, for a anti-reflection coating or a dielectric mirror coating, to work well enough across the visible light spectrum given the other limitations in a bin. You don't as you seem to imply in your first reply have only 4 parameters to use: you have two parameters per layer (refractive index and thickness) and N (say 64) layers. Solve the Fresnel equations for that stack (assuming you can manufacture arbitrary stacks) and you can minimize the phase differences to an arbitrary level. As you can minimize the reflection in an AR coating or maximize the reflection in a dielectric mirror.

Human acuity is only about 1 minute of arc with some extra processing features in the brain that can exceed that for very special cases (verier positioning and the like). Bins even those roofs that don't have phase correction regularly exceed this. They may have other problems (scatter, diffraction spikes, contrast issues) but in a well designed bin thaty actually come quite close.

Sure you a roof can't better a porro but it can be indistinguishable for the human eye.

So to address thee other questions you raised in an early: why does none make top end porros any more?

Roofs do have real advantages which you ignore in your reply. It's not just optical quality. It's ergonomics and other features that count too.

• Roofs are more compact than porros.
• Roofs are lighter than porros.
• Roofs are easier to make waterproof and fogproof (and stay that way for life) than porros because you can seal the barrels. Porros could use internal focusing to do this (and some do) but they all seem to have a narrow FOV (perhaps because an internal focusing mechanism are more limited in a porro design?).
• Roofs were more rugged than porros. Though this was due to gluing prisms in place and the prisms sub-assemblies being supported on all sides by the barrel something you can't do in porro as the light path is in the way. Modern Chinese porros (eg. the Leupold Yosemite) show that you can use these same techniques to make a porro very nearly as rugged as a roof.

So why do the Euro 3 not make top end porros? Money and the market.

Which would you choose? 20% of $500 or 20% of $2000? Bin makers know that it's more expensive to make roofs but that they can sell them for more. So for a given margin they make more revenue. They also know that they can make more "new" innovations so as to compete with other makers. For porros any moderately competent optical company can do it. And there are good optical companies in places like China where the costs are much less than Europe. But they still have to deal with the consumers. Will they buy them?

But why did porros go "out of style"? Social trends like the expert birders in the 1970s using the expensive roof prisms bins because they were waterproof and rugged (real positive effects as the porros weren't). Of course other birders notice that the alpha birders are using roofs and want to be like them. And then they realize that they can be more compact and lighter too. Remember the good old days of > 32oz 8x40s? People haven't forgotten especially those that voted with their necks too.

There were also manufacturing trends too. A lot of the old porro makers were older companies stuck with older ways of doing things (e.g. making porros easier to recollimate rather than making it more difficult for them to get out of collimation). They came to be seen as old fashioned. Leica (then Leitz) got out of the porro design business in 1960 to focus on roofs. They still sold porros but there wasn't a new porro design after 1962. Zeiss followed a little later. Compare that to, say , Swift, who didn't make a move to roofs until the 1990s.

Birders don't just choose bins for their optical qualities. That would be a typical "geek" bias. They have many different reasons for choosing a particular bin: feel, weight, shape, FOV, AFOV, grip, balance, perceived benefits (ruggedness), brand, etc. These features have nothing to do with the "quality of the view". We've seen a parallel evolution in the automobile too: it's not about 0-60 time or horsepower for most people. It's cupholders and comfy seats.

There is also a behavioral economics effect called "price anchoring" by which people (both buyers and sellers) fix a lower bound price price they are willing to accept. The price anchors for porros and roofs have split in most peoples minds. People are happily anchored on an alpha bin must cost > $1000. So they'll pay that.

e.g. http://sloanreview.mit.edu/wsj/insight/interview/2008/09/22/

So roofs can get away with charging more because, after all "that's what you have to spend for quality": the same sort of argument applied to preferring a Rolex mechanical watch with worse timekeeping capability than the $20 Casio.

One interesting problem for the upper-mid and (perhaps) the alpha roofs is coming from Chinese optics manufacturers moving upmarket. So we have no-name brands like Promaster and Hawke (sorry, Hawke!) putting out very, very good roof bins in the lower middle price range (currently $400 to $500). These bins are one third to a quarter the price of the Alpha bins if not quite at the same quality point. But they're close enought for most people. If people buy on "good enough" quality and not brand name what is going to happen to the upper end of the market? Actually I think the Euro 3 (or should that be "The Axis" 4 if we include Nikon) have brand name recognition to maintain their place. But I think the others in the market will struggle.

So you might think after all that I'm a rabid roofie fan? Not really.

I actually agree with your premise. I just think your making an invalid argument for it. As I've pointed out in my own bins reviews inexpensive modern porros are beatings roofs costing two to three times the price but still people buy roofs (even people like me!).

So what can be done?

You can make porros that equal the top end roofs for much less. You could apply modern techniques to making porros that would result in lighter (use GRP not metal), more rugged (glue the prisms in place), with internal focusers (can you get a wide FOV?), with state of the art multilayer AR coatings plus hydro and lipophobic coatings. Pay attention to enclosure design (we have the CAD technology and injection modling to do that now). They might even deal with stray light better than most roofs (roof biggest weakness, IMHO, excepting the Alpha roofs were they actually care about that during the design).

The problem is will people buy these hypothetical top end porros at middle range prices? I suspect that unless you are an "optics geek" (if you are reading this then you are one) people don't buy "big clunky bins" but prefer the "cuter, less clunky ones".

For some reason the US market has been conditioned (conned) to believe that just because a product is more expensive it HAS to be better (even if it isn't). That is probably why people hang onto their Swift 8.5x ED lens porros. At a recent Japanese star party there were many questions from visitors to Nikon reps asking why the Nikon SEs weren't made in waterproof versions the way the Action Extremes are made. The Pentax reps got similar questions about why their CF waterproof porros didn't utilize the Pentax ED objective lenses to go with their aspherical eyepieces and the answers came back that this would make the roofers by both Nikon and Pentax look so obviously bad that there would be lots of "market confusion".

Japanese companies try to avoid market confusion as much as possible because then they can't sell as many super-expensive roof prism binoculars with slightly more convenient formats against their own brand of high end porro prism binoculars with much better optical images, and at half the price. That's probably why Swaro discontinued the porro 10x50 SLC.

Click to expand...

I agree with all of this. I'd love to see a waterproof SE (how did people manage without waterproof porros in the past?). Or a 820 with real full field ER. Or Pentax porros with ED and a better FOV.

But the Swift 820ED have their own problems. Eye relief. It's speced at 17mm but it's perhaps 12mm usable ER. Not enough for the aging eyeglass wearing bino buyers (which are the majority today).

I suspect that either the design of roofs have decoupled the focusing from the eyepieces has results in some freedom to make eyepieces with much better ER than porros had. Or perhaps the older porro makers didn't care about ER and the roof makers did. But the consumers cared. So this would be a demographic change in birders driving the shift from porros to roofs. And the less innovative porro makers didn't see this coming?

There's no conning involved. People bought on features they liked and the market evolved.

This all brings to mind the "The Innovator's Dilemma". This sort of change is not going to be made by someone already in the business because to make that change would destroy very profitable parts of their market.

http://en.wikipedia.org/wiki/Disruptive_technology

Perhaps we'll see a range of (Chinese made) Kansas Bird Ranch porro bins in the near future? You can offer them the features they want (see above) in a porro for a lower price. They should flock to them!

...Swift, who didn't make a move to roofs until the 1990s.

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A'hem. Swift-Anderson imported and distributed Hensoldt Dialyt-prisms as far back as 1930. You could buy a nice marine model 7x50 for the meager sum of $120 at that time. I believe these Hensoldts later formed the basis for Zeiss' A-K BGAT series.

Swift marketed Japanese made roof prism binoculars from 1968 or earlier with the Mark II Trilyte 7x35 and 9x35. These and other models continued to the present day.

I stand corrected but designed by HH Swift and his team? Or were they OEMed designs?

Distribution is perhaps recognizing the problem

Hmmm, I see there's even a set of Trilyte's for sale locally!

http://seattle.craigslist.org/sno/spo/862456865.html

Is there a comprehensive list of Swift models (like the ones accumulated for Zeiss and Leitz/Leica?

Hi Kevin,

I suspect that most of the optical engineering was done by the Japanese OEMs, although it's hard to say where the overall specs originated.

There are pretty good Excel spreadsheets by Gene Harryman covering Japanese bins. He also has one exclusively on Swift. Unfortunately, I can't manage to attach them here. You might find them on Peter's list.

Some of the comments on this thread are thought provoking, although as I understand it P-coating simultaneously effects the phase angles of all frequencies in the spectrum, i.e., as a continuum. The secret is to find coatings that nullify the exact phase lead/lag distribution resulting from the geometry and particular glass type used. It seems to me the opticians have done a great job at this, to the point where it's no longer an image quality issue. For those who think otherwise, ... you know, prove it.

Just my opinion, of course, but it would be hard to find a thread that credibly addresses the esoterica of P-coating quality between any two binoculars — even expensive vs. cheap ones.

Ed
PS. This .pdf file kinda says it without the Fourier transforms and Bessel functions of the second kind. |:d|

ksbird/foxranch said:

A couple of years ago a salesperson working for the nearby Cabelas took his Swaro 10x50 SLC porros to a demo of the new (then) Swaro SLC 10x50 roofer.

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There have never been porro design models designated SLC.

ksbird/foxranch said:

That's probably why Swaro discontinued the porro 10x50 SLC.

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there was not need to discontinue them as they never existed in the first place.

There had been porros called SL, but non called SLC.

PS: and they did not have inferior coatings either.

ThoLa said:

There have never been porro design models designated SLC.



there was not need to discontinue them as they never existed in the first place.

There had been porros called SL, but non called SLC.

PS: and they did not have inferior coatings either.

Click to expand...

Hi Thomas, I thought I was missing something with the Swarovski 10x50 SLC Porro and had never heard of it.:eek!: At the the time Ksbird,foxranch talks about the Cabelas salesperson taking this 10x50 SL model and was compared to the then new 10x50SLC roof the roof was most likely non phase coated. I have a Swarovski 7x30 SLcompact [SLC] non phase coated and still have the catalog I bought it from and they show just the 1-traditional Swarovski porro,2-the SL series porro, 3- the 7x30 & 8x30 SLcompact [SLC] roof prism series and there are no full size SLC series roofs. I am not sure of when the full size roof prism where made by Swarovski and I wish I had added a date to my catalog when I first received it. I have attached a picture of what my box that my 7x30 SLC came in looked like and Swarovski was still using this box in 1991 when the fellow that bought his 8x30 SLC and then sold it in August of this year.This fellow kindly left me use his picture from his ad and also sent me a Swarovski catalog dated Edition 4/ April 88. This catalog only shows the SL, traditional and 7x30SLC and the 8x30 WA SLC in it, no full size SLC models at all.
Regards,Steve

elkcub said:

PS. This .pdf file kinda says it without the Fourier transforms and Bessel functions of the second kind. |:d|

Click to expand...

Thanks for the other data but that Astromomics explanation of phase compensation is bogus

No mention of polarization components and their phase lag which is what is actually compensated for. The last time this was posted I posted a follow up that corrected it (search the forums!).

You summary is much better.

My original point in posting this was to emphasize the following (though I didn't say it:

• Roofs prisms first came into use at the beginning of the century
• The theoretical need for phase compensation was realized i in the early 1940.
• A practical method did not become available until 1966 (but mainly for use in interferometers and other instruments)
• Commercial phase compensated roof prisms bins became available in 1988 as Zeiss' P* coating. Others followed.

The best example of a controlled experiment as to if PC works I've reported here before comparing three models of Zeiss Dialyt with the same optics but built at different times. One with no PC and single AR coating. The next with no PC and multilayer AR coating (T*). The final one was a post-1988 build multilayer AR coating (T*) and phase-compensation (P*). The biggest difference was in the final model.

Remember the good old days when a model could stay in the market for a couple of decades!

When the Chinese got into this market they didn't have PC roofs. The Chinese roofs of course had other interesting problems making "good" bins: poor component QA, poor general QA, poor design (e.g stray light issues). They didn't have PC either but most people started to think "no PC" == "terrible view" (which some were but that wasn't just because they had no PC) not "softer and lower contrast along the axis perpendicular to the the roof edge" if they'd managed to deal with the other aberrations, distortions and stray light.

Out of all of this I find the socilogical aspects of roofs vs porros to be the most interesting. Why did people change?

Kevin,

Are you kidding? I can't even find my own stuff on BF.

I agree the Astronomics article doesn't provide much insight into the underlying optical physics, but "bogus" is a strong word. Is it wrong, or just incomplete?

...Out of all of this I find the sociological aspects of roofs vs porros to be the most interesting. Why did people change?

Click to expand...

You know, I like the way you put it. Social aspects are fascinating.

The 'wisdom of the market' seems to be saying that roof products meet the public need better than Porros, at least beyond some price point. Most folks are not binocular mavens, so for them subtle optical distinctions don't matter.

When I visit REI and see that they are selling large quantities of bubble-pack bins to outdoor nature enthusiasts, it also makes me scratch my head. In that case, however, the bins are Porros, most often, and below the roof's price point. So, I suspect that poor quality is being conditioned into the public mind for Porro designs, which reinforces the idea that higher priced roofs must be better.

Ed

mooreorless said:

Hi Thomas, I thought I was missing something with the Swarovski 10x50 SLC Porro and had never heard of it.:eek!: At the the time Ksbird,foxranch talks about the Cabelas salesperson taking this 10x50 SL model and was compared to the then new 10x50SLC roof the roof was most likely non phase coated. I have a Swarovski 7x30 SLcompact [SLC] non phase coated and still have the catalog I bought it from and they show just the 1-traditional Swarovski porro,2-the SL series porro, 3- the 7x30 & 8x30 SLcompact [SLC] roof prism series and there are no full size SLC series roofs. I am not sure of when the full size roof prism where made by Swarovski and I wish I had added a date to my catalog when I first received it. I have attached a picture of what my box that my 7x30 SLC came in looked like and Swarovski was still using this box in 1991 when the fellow that bought his 8x30 SLC and then sold it in August of this year.This fellow kindly left me use his picture from his ad and also sent me a Swarovski catalog dated Edition 4/ April 88. This catalog only shows the SL, traditional and 7x30SLC and the 8x30 WA SLC in it, no full size SLC models at all.
Regards,Steve

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Steve,

I own a phase corrected 8x30 SLC Mk II purchased about 1995. I assume yours isn't waterproof and has no glass plate in front of the moving objective. True?

Does the current 8x30 SLC still uses a flat plate with moving objective — or does it have an internal focusing lens like the larger (and smaller) SLCs?

Ed

Hi Ed,Sorry I didn't see this until this evening. When I bought my 7x30SLC is was supposed to be WP. You are right this binocular doesn't have the glass plate in front of the objective, so I guess it is just water resistant. I don't imagine the 1991 model 8x30 SLC was phase/coated either like mine. The picture I have of the 1991 model doesn't have the glass plate in front of the moving objective. I returned my pair to SONA in 2003 and at that time I asked if I could upgrade to phase/coating and they told me only the full size SLC could be upgraded to phase coating. Zeiss is supposed to have come out with p-coatings in 1988, so I would think it would of taken a while for the rest to catch up.
Regards,Steve