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

I guess I must have missed a few "reasonings" in this thread because from what I can tell, nearly every reviewer who reviews the Nikon SE series says they are superior in image quality to any roofer out in the market today and only other porros (possibly) like the Fujinon FMT series are comparable. If the differences in sharpness, color balance etc. between the SE Nikons and the best roofers is not due to s and p phase distortion, what is the problem the roofers have? In addition, why can't Nikon use the same objectives or eyepieces from the SEs in their LX or HGE models if that is where the "SE superiority" rests. Unless the use of an internal focusing lens is the problem with the eyepiece/objective designs from the SE series)?

So while the amount of additional s and p phase distortion may seem negligible compared to porros which have no s and p phase distortion at all, assuming all other things like multicoatings are equal, why is it that the Nikon and Fujinon porros are nearly unanimously chosen as having superior image making ability?

Also I assume that there are few if any metal housing roofers to choose from so it is difficult to compare metal housing porros to metal housing roofers, but whenever I have a pair of each with similar housings, there doesn't seem to be much weight differential (Leupold Yosemite 8x30s vs Zeiss Diafun roofers for example). The same is true for size. Roofers are by design Narrower, but that doesn't mean that they are required to be much smaller. The Zeiss Diafun 8x30s I have are not smaller than many of the 8x30 porros I have, but they are narrower. This narrow hand-holding position is very uncomfortable for me almost all the time and whenever I have visitors in the winter, bundled up in their thick down coats, they seem to have trouble with the hand-holding position in front of their eyes as well (because the coats interfere). I guess that for me, a hand position slightly in front of but outside my outer eye socket ridges is much more comfortable than directly in front of my eyes.

While you mentioned the advantages that seem to show up with roofers, you didn't seem to list the advantages that usually show up in porros

#1 In 7x and 8x porro models (for certain), almost all porros have a substantially wider field of view than roofers. The 7x35 Nikon Action Extreme waterproof binocular with a 498ft wide FOV at 1000yds is likely a much wider FOV than ANY 7x/8x roofer made today.

#2 It is possible to make a binocular in a porro that is accepted as the Reference Standard by which all other binoculars are compared for roughly half the selling price of the highest end roofers that produce images not quite as good. This could easily translate into 2 pairs of Nikon SEs for a family to use instead of one high end Swaro, Leica or Zeiss roofer that produces images that aren't quite as good as the SEs.

#3 Truly Excellent images, can be produced in an ultra-lightweight, waterproof porro binocular like the Leupold 6x30 at prices that let small women and children (even those who wear eyeglasses) enjoy superb images when equivalent image quality wouldn't be even approachable in a roofer of comparable, weight and price (I'm assuming that all roofers are water resistant now).

So while some older ED porro binocular designs may have short eye relief (porros have the same freedom to use large eye lenses that can produce full wide angle views as roofer [in fact probably wider FOV because roofers generally have narrower FOV compared to porros]) obviously not all porro makers use larger eye lens eyepiece designs to maximize the use of their superior FOV. Maybe it is just a cost decision because if you look at a Yukon porro 7x50W with its wide FOV and the huge eye lenses, you know that these eye lens designs have been around for a long time (the Yukon 7x50W is a copy of the Jenoptem 7x50W but with even longer eye relief). I have a cheap Chinese Breaker 10.5x55 porro (labeled 14x60 LE???) with 22mm of eye relief and fold down eyecups that is a favorite for visitors who wear eyeglasses. The Steiner 8x30 porros models all have excellent eye relief due to huge eye lenses and fold down rubber eyecups (Steiner makes 62 porro 8x30 models I think, or perhaps they just add another 8x30 porro model each week), and these Steiners are all waterproof, lightweight and small.

So it would seem like the first ultra-high end porro that is made with large eye lenses and long eye relief (allowing for the full view of most porro design's extra large FOV), using whatever lens/coating technology is used in the Nikon SE series or Fujinon FMT series for superior sharpness (or ED/Flourite glass or aspherical eyepiece design), and with an internal CF design like Pentax uses in their 7x50 DCF WP II, may be expensive (but probably not as expensive as the high end Swaro, Leica or Zeiss models), and with a lightweight fiber/poly body material, will likely be a binocular superior or equal in so many aspects of viewing/using that roofers will never be able to catch up except for people who prefer having a narrower body style more than the best imaging.

I don't quite get the porro vs roofs holding problem, but people have their preferences. I can hold pretty much any binocular as long as it takes to see the bird. Even 50mm. The rest of the time, with the binoculars around the neck, the weight is the issue.

OK, back to phase coatings.

Also I assume that there are few if any metal housing roofers to choose from

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Bad assumption. Most middle and high end roofs have metal cases. The same case is always going to be heavier in a porro because a tube (the roof) is always going to be lighter than the same tube with a box in it i.e. the surface area of an porro enclose will always be large than the same roof because the objectives are spaced further apart and the bins are the same height (with the same focal length and focal ratio). But with a light case material (and most of the weight in the glass) this should be a small fraction of the total weight but it will always be the case.

Do you have references for the reviews you mention? When where the review made? Are they comparing current roofs? Or roofs from 2000 or whenever the SE was released? Objective measurements or just looking through the bins? It's a big claim so I'd like to see the evidence it's based on.

I don't list the advantages of porros because I fully acknowledge them and said so in my original post. See for example my Budget Bin review were I point out how much better cheap porros are than even mid-range roofs. I was trying to point out that your original argument "you can't phase compensate a roof prism correctly" is bogus but the conclusions you hold to are correct (good porros are cheaper than good roofs).

Just because they can (and do make porros) with performance that at least equals the best roofs for half the price doesn't mean that the optics makers want to build them. Because they can make more money making roofs and their customers want to buy them. Optics businesses are businesses first and optics companies second. That was the second part of my post.

who prefer having a narrower body style more than the best imaging.

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And I suspect you may find that ergonomics trumps optics for most optics customers. Even for quite a few birders. This is the driving force of the demise of the porro even when we have good, light, cheap bins like the Yosemite or excellent mid-priced bins like the E, E2 or SE.

If you want to fix this (as I suggested in my previous post) then you need to get into the bin business making new high quality porros for half the price of the alpha roofs using all the latest innovations. I'd buy one! There's a few others here who would buy them too. But I fear after that you might struggle to find customers. That's the real root of the problem.

Finally, I'm waiting for my Nikon SE to arrive. It'll go really nicely with my 6x30 Yosemite and my Celestron Ultima DX 8x32. Oh, and I'm waiting for an 8x30 Yosemite to arrive too. Clearly I'm a roof nut

elkcub said:

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.

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I think Peter Dunne sums it up here best (in the EL "overview"):

This is not the first time I have gone through this exercise[of working with an optics company as a user representative]. In 1985, Bausch and Lomb established an advisory council--a think tank of birding professionals whose needs were to be forged in glass. The product was the original B&L Elite 8 x 42, a binocular that was a decade ahead of its time and whose optical package can still outperform all but a handful of the best instruments produced today.

But it was twelve years later and the birding optics frontier had moved on. Where the B&L think tank was intent upon optical excellence, the Swarovski task force concentrated upon ergonomic design, superior depth of field, zero color bias--considerations that had never even come to the floor when the Elite was born.

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That's the difference between then and now or old and new: those that thought the optics was all that the customer cared about in the bin are no longer making bins (porro or roof).

The biggest problem for a porro-only company would be convincing the customers that the bins where "not their Dad's porros". They would have made that decision without even seeing the bins. And especially without looking through them.

I think that other comments about why roofs may be sucessful is because they don't look "like your Dad's bins" is probably on the money, especially at the low end of the market.

Finally, I'm waiting for my Nikon SE to arrive. It'll go really nicely with my 6x30 Yosemite and my Celestron Ultima DX 8x32. Oh, and I'm waiting for an 8x30 Yosemite to arrive too. Clearly I'm a roof nut

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You meant porro. Yes, the Yosemites are very cute.

With my porro 8x42s, the weight around the neck is the issue. I hold both porros and roofs with slightly bent arms, the same roughly 90 degree angle relative to the binoculars. I don't really care if the fingers touch as long as the thumbs have a good grip.

I like to carry the roofs one handed at times, the porros are harder to grip. I use the hand to give the neck a break.

Tero said:

Clearly I'm a roof nut

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You meant porro.

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I was being ironic or perhaps sarcastic, Tero ...

Well, better a roof nut than a nut on my roof.

Kevin Purcell said:

That's the difference between then and now or old and new: those that thought the optics was all that the customer cared about in the bin are no longer making bins (porro or roof).

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I take your general point, but just to set the record straight, Bushnell is the direct descendant of the portion of Bausch & Lomb that produced sports optics and related products, and as you know, Bushnell is very much still in the business of making (or at least designing and marketing) bins. Furthermore, I don't think it's fair to argue that B&L/Bushnell were/are only concerned with optical excellence. The original Elite was a standout for its birder optimized optics, but much of that optimization had to do with its specs for eye relief, close focus, and focus speed, not improvements in raw optical quality. Moreover, the original Elite was also a standout for its superb ergonomics (I wish there were current models with similarly slim barrels and focus knob placement), which did not come about by accident. The first generation waterproof Elite was also a standout for its radical body shape (too extreme in my opinion) that demonstrated much interest (even if misdirected) in the question of ergonomics and style. I think you've misinterpreted Pete Dunne's point. It's not that B&L was any less interested in ergonomics, or Swarovski any less interested in optics, but that by the time the ELs were being developed, top-end roof-prism optics had been so greatly improved (especially w/respect to specs that met the needs of birders) that to make a profoundly distinctive landmark product its designers had to make improvements in optics and ergonomics (with perhaps more room available for improvement/change in the areas of ergonomics/styling than optics, though the EL reached new maxima in both) by optimizing characteristics that previously received little attention because they were inconsequential in comparison to other specs that up until the 1990s were often not good for birders.

--AP

...So while the amount of additional s and p phase distortion may seem negligible compared to porros which have no s and p phase distortion at all, assuming all other things like multicoatings are equal, why is it that the Nikon and Fujinon porros are nearly unanimously chosen as having superior image making ability?

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KSbird/FoxRanch,

Based on the reference Kevin provided in post #1, it would seem that all light reflected by a prism is s-polarized and all light refracted through the prism is p-polarized. http://en.wikipedia.org/wiki/Brewster's_angle The important discovery of p-coating appears to have taken advantage of this property, and when applied properly produces a phase delay for the shorter light path in the roof design. Polarization, however, is a physical property of both types of prism, and shouldn't be thought of as an optical aberration that applies to one and not the other. The image produced by an uncorrected roof design is simply phase incoherent, and, therefore, suffers from frequency cancellation effects as discussed above.

Ed

elkcub said:

Based on the reference Kevin provided in post #1, it would seem that all light reflected by a prism is s-polarized and all light refracted through the prism is p-polarized. http://en.wikipedia.org/wiki/Brewster's_angle

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That would only be true at the Brewster Angle. I included the link as a more general explanation of s- p-polarization for those that had not seen the term before.

The Fresnel Equations give the more general solution.

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

See the graphs in the article: the first is for reflection "off the surface of a prisms"; the second is for "reflection inside a prism" (total internal reflection)

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

A little bit of research has shown that each "reflection-type film-substrate retarder" layer works at a particular color. You make a phase compensating coating in a multi-multilayer optimizing each of the layer thickness and materials to give a constant phase delay across the optical spectrum.

Just the "same" way as you optimize a multi-multilayer for an anti-reflection coating or as a reflective coating (dielectric mirror). Obviously you are optimziing on different properties but in these other cases you can get a "flat response" with current designs (64 layers seem popular).

Kevin Purcell said:

That would only be true at the Brewster Angle. I included the link as a more general explanation of s- p-polarization for those that had not seen the term before.

The Fresnel Equations give the more general solution.

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

See the graphs in the article: the first is for reflection "off the surface of a prisms"; the second is for "reflection inside a prism" (total internal reflection)

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

A little bit of research has shown that each "reflection-type film-substrate retarder" layer works at a particular color. You make a phase compensating coating in a multi-multilayer optimizing each of the layer thickness and materials to give a constant phase delay across the optical spectrum.

Just the "same" way as you optimize a multi-multilayer for an anti-reflection coating or as a reflective coating (dielectric mirror). Obviously you are optimziing on different properties but in these other cases you can get a "flat response" with current designs (64 layers seem popular).

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Kevin,

I agree, thanks for the correction. The Fresnel equations express the relationship between the reflection and transmission coefficients based on the refractive index.

One problem I have with Wikipedia is that it can get rather frenetic moving from one thing to another. Nonetheless, having no book to study this particular subject, one of my references is a Wiki article on binoculars. I've pasted the section about phase correction below, although it doesn't get into the physics or makeup of the coating itself. I don't have any references to frequency specific aspects of layers, so I'd appreciate any digestible reference you have. But, my willingness to pay for articles is constrained by the limited extent of my curiosity.

Ed
http://en.wikipedia.org/wiki/Binoculars

Roof prism phase correction coating
In binoculars with roof prisms multiple internal reflections in a roof prism cause a polarization-dependent phase-lag of the transmitted light, in a manner similar to a Fresnel rhomb.
The light path through the roof prism is split in two paths that reflect on either side of the roof ridge. One half of the light reflects from roof surface 1 to roof surface 2. The other half of the light reflects from roof surface 2 to roof surface 1. During any reflection, including total internal reflection inside a prism, unpolarized light becomes partially polarized. During subsequent reflections the direction of this polarization vector is changed but it is changed differently for each path in a manner similar to a Foucault pendulum. When the light following the two paths are recombined the polarization vectors of each path do not coincide. The angle between the two polarization vector called the phase shift, or the geometric phase, or the Berry phase.
In a roof prism without a phase correcting coating interference between the two paths with different geometric phase results in an varying intensity distribution in the image reducing apparent contrast and resolution compared to a porro prism erecting system. This effect can be seen in the elongation of the Airy disk [1] in the same direction as the crest of the roof.
The unwanted interference effects are suppressed by vapour depositing a special dielectric coating known as a phase-correction coating or P-coating on the roof surfaces of the roof prism. This coating corrects for the difference in geometric phase between the two paths so both have effectively the same phase shift and no interference degrades the image.
Binoculars using either a Schmidt-Pechan roof prism or a Abbe-Koenig roof prism benefit from phase coatings. Porro prism binoculars do not recombine beams after following two paths with different phase and so do not benefit from a phase coating.

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He, hee.

I wrote pretty much all of that part of the wikipedia entry.

It needs revising to put the polarization stuff I added to Schmidt Pechan prism and the reference mentioned here. The reason I wrote it and got off on this track (actually trying to understand what's going on) is that there wasn't anything in the binoc entry on coatings except a little on AR coatings.

A decent textbook would be excellent though they are very expensive. A decent (state) university library can help though.

What a stinker. I was noting a strong similarity with Freeman and Hull's discussion in Optics, Ed. 11, 2004 pp. 403-407, so I take it that expensive book is one of your sources. I found it recently at a good price. If there a specific reference to P-coating I haven't come across it yet.

Ed

I didn't get it from there. One can't just copy non-GFDL text for Wikipedia except from other wikipedia parts (that are already GFDL). I recall starting from a couple of bits from other wikipedia entries and then expanding that.

I suspect that if you are an optics person you farm this out to the tame thin films guy (or parts maker) but it is difficult to find an explaination of what's going on. Hence this thread.

Sorry, didn't mean to imply that copying is going in. I was really thinking about the Fresnel equations and Brewster's angle writeups that are related more coherently in the Freeman and Hull book. The international version can be gotten from ABE, incidentally, for about $17 (ISBN: 0750642483). It's well worth it.

So far your explanation of P-coating is the most informative I've read. Keep up the good work.

Ed

No implication was taken. Though I have noticed myself when consulting a textbook to write something up (not just on WP) that one often unconsciously "nicks" a sentence or two. I try to avoid that, if possible. I think if you read Steve Ingraham's explaination of SP roof prisms (linked in the article) you might see some borrowed ideas but no stolen text (I was quite careful about that!).

The current explanation is better than nothing but it still has a lot of hand waving (not even mention of s- and p-polarized interference or the structure of ). But hopefully it will improve over time.

It seems the design of most "reflection-type film-substrate retarder" as they're sometimes called The the system will work as a retarder if the refractive indices of the ambient N0, film N1 and substrate N2 are such that N1 <= square root of N0N2 .

So my working hypothesis is you arrange the films to preferentially reflect one the polarizations at the lower interface and allow the "leading" polarization through the interface. Then you propagate that through the film reflect it from a outermost interface then propagating through the film again (so being delayed) until it meets back up with the other polarization and now they're both in phase. I suspect there is an extra (non-obvious) trick that requires three layers but I suspect it has something to do with selecting the polarization. When you do this you can get the phase delay to zero at one frequency. By stacking these blocks (and probably optimizing across the whole set of layers) you can get zero phase delay between s- and p- components of the reflected wave (or any arbitrary phase delay you want to compensate for other delays in the system).

Is there an emoticon for handwaving?

Of course as ksbird would say that's an awful lot of trouble to go to when a porro erector will just do it for free. And yes, I agree with him on that. It is.

Is there an emoticon for hand waving?

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How's this? :brains:

I have no idea if the roof prism does or does not introduce any noticeable image degradation when well made and coated. But I recall someone stating that roof prism bins tend to have faster objectives - i.e. shorter focal lengths - which will introduce aberrations. In addition faster objectives will require more sophisticated eyepieces, which will increase cost, and perhaps extra aberrations from the eyepieces. In addition most roof prism bins focus by means of a sliding lens between the objective and the prism. My suspicion is that the focus lens is a major cause of CA in many roof prism bins, especially cheap ones. To my eye roof prism bins which focus by moving the objective tend to have noticeably better image quality than others.

Anyway, I doubt that major manufacturers will introduce top grade porro bins, sadly. Fashion, weight and bulk surely mitigate against them.

Kevin perhaps I am not understanding your definition of "one frequency", which I thought referred to One Frequency of Light. I am specifically commenting on this quote from your most recent post

"So my working hypothesis is you arrange the films to preferentially reflect one the polarizations at the lower interface and allow the "leading" polarization through the interface. Then you propagate that through the film reflect it from a outermost interface then propagating through the film again (so being delayed) until it meets back up with the other polarization and now they're both in phase. I suspect there is an extra (non-obvious) trick that requires three layers but I suspect it has something to do with selecting the polarization. When you do this you can get the phase delay to zero at one frequency"

Since there are an Infinite number of visible light frequencies visible across the full spectrum of our ability to see, and at most, companies like Zeiss might be compensating for the s and p phase incoherence at 20-30 of these frequencies, 99+% of the light frequencies coming into the light path and reaching the eye are not coherent. The Zeiss compensation in their roofers might be better than other roofers, but it is still at least 100x worse than a well made porro.

I never got an answer on this but why is it that the best images for birding seem to be produced by the Nikon SE series bins (porros) (or possibly the Fujinon FMT series)? If Nikon can make the most highly rated bins image-wise, it is surprising that they don't make the same objective and eyepieces for a roofer, unless this would show up the obvious inferiority of roofers due to phase incoherence.

I offered the advantages that most porros offer and they seemed very important (wider fields generally, much lower cost for the #1 rated bin image-wise according to reviewers, which is the Nikon SE porro system, etc.). You said there was a similar phase incoherence problem in porros but never defined how it would work when the light path enters or reflects through porro prisms at 180 degrees or 90 degrees and any other light reflections do not continue in the light path, they either reflect back out of the binocular, or are disbursed or reflected into baffles or blackened-frosted prism sides. When the offending out-of-phase light waves doesn't get to your eye there isn't a phase coherence problem.

Leica created all the misunderstanding/marketing-effect about roofers with their early Trinovids. This mis-perception in the market has continued to this day and in much the same way that we lost about 90 years of electric car development when we didn't support the early electric cars, the world's largest binocular markets got swept up into the huge mis-perception that just because roof prism binoculars were more expensive (like the early Trinovids), they had to be able to produce a better visual image, which is patently untrue (like the notably "soft" images produced by the early Trinovids).

For years the US military has been hoping there was some kind of straight-line design binocular (like a roof prism design binocular) that can produce as sharp of an image as a porro prism binocular, because roofers might be easier to make waterproof, and they could be easier to make rugged, and they could be easier for soldiers to transport. But no roof prism binocular has passed the minimum standard for sharpness (to know the enemy, you must be able to ID the enemy). Right now Fujinon makes US military binoculars using their flat field designs. Other companies are close, but all the competitors end up being porros because they produce the best visual images. The older East German 7x40 porro prism military binocular is still in great demand and 90% of all the designs now made after testing for most military are prorro prism designs. Sure the Bundeswehr buys some roof prism bins, but only under duress due to the importance of Zeiss, and Zeiss' unwillingness to make porros for the military for "marketing confusion" reasons (in other words if Zeiss made a great porro prism bin for the German military, consumers would want to get them in a CF design and this would make Zeiss roofers look bad). It's the same reason Nikon won't make a waterproof version of the SE series.

It works exactly at one frequency and less well at small offsets (the error increasing away) when you build a stack you choose a series of frequencies and optimize each of these.

This is exactly the way you design AR, dielectric mirrors and other thin layer systems.

You make the mistake of "infinite number of frequencies". There is but you can't perceive them all. You have three different detectors (cones) in the eye. Each works over a band of frequencies and your brain devotes a lot of effort in assigning colors to portions of the image. You eye isn't perfect. It isn't a spectrometer. So you have to make the correction only good enough to work within the limits of the detector which in this case is three color bands. In real lilfe you optimize across an octave or so (the wide of visible light band) but you bias the curve to the eye's response (which isn't flat either).

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

It's all about tolerances. There are no perfect systems out there. Including the eye.

BTW, with your logic you can't use any AR in your ideal porro because they're optimized for one frequency (single layer AR) or only a few of the many frequencies.

Read a bit about approximation theory if you don't get any of this.

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

I'm sure the M24 is bought under duress too . For the M24 the design goal was to make a "compact" bin that would fit into a BDU pocket usable by any solider. This constraint wouldn't be met by a 7x30 porro. It doesn't fit.

But I suspect the general "porro versus roof" for the military comes down to cost. The porros are cheaper than roofs and for most military uses compactness or even light weight is not the issue with plenty of fit twenty something users. You can build porros today as robust as roof (pretty much - the eyepieces are a bit more vulnerable to a shear force because they're not in a single tube).

You said there was a similar phase incoherence problem in porros but never defined how it would work when the light path enters or reflects through porro prisms at 180 degrees or 90 degrees and any other light reflections do not continue in the light path, they either reflect back out of the binocular, or are disbursed or reflected into baffles or blackened-frosted prism sides. When the offending out-of-phase light waves doesn't get to your eye there isn't a phase coherence problem.

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I didn't say that. I think you misread something I wrote. The light output from porros though is polarized (due to reflection) but that doesn't have any effect on resolution. Maybe you misread that?

The Zeiss compensation in their roofers might be better than other roofers, but it is still at least 100x worse than a well made porro.

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100x worse, eh?

You know that 97.2% of statistics are made up?

As I've said multiple times now: manufacturers make more money from roofs.

People buy them because they like them. Quite a few people with good eyes for optics. That's why they make the roofs. They don't make the porros because they don't make as much money and (as you say) they would be just as good (not a lot better). The good roofs actually work fine (despite your protestations) and make the makers a lot of money. QED.

The only way out of this is a new company. To sell to logical cheapskate buyers (i.e. the military) or to make porros so attractive (i.e. cheap and good) that people flock to them despite them being bigger (and for quite a few more awkward to handle). But to do that you need a company that doesn't make roofs. It's a market gap but I suspect people like their ergonomics too.

I think it's quite clear that this is a religious argument not a logical one.