It's here a reliable way to tell if you really have phase coating? (1 Viewer)

Phase coating costs money. Yet I have some across several bins that claim to be phase coated yet are actually very cheap. I even bought a pair (I paid £40).

Now, we know that phase coating makes for a brighter image (I won't go into the physics). But that doesn't really help us determine whether a particular pair of bins has PC. It would be easy for a re-label minor brand to tell fibs on this. Or, indeed, to innocently pass on fibs from the Chinese manufacturer.

Is there a reliable way to tell?

PS For that matter, if an obscure brand claims to offer "ED" glass, how can we know whether they are telling the truth? Is there even an accepted industry-wide standard for what constitutes ED?

NB, I'm not asking what ED is, I know what it is (or think I do!). I'm just wondering whether there is an industry standard which would hold up, for example, in a court of law. Hypothetically.

I think that in the case of very cheap binoculars, Porro prisms are better than Roof prisms, with regard to achieving a satisfactory overall optical quality.
Phase Coating is something very critical and it is better to buy a Roof prism binoculars with medium or high cost, to be sure to get something really good.
If your budget does not allow that, then it is better to buy a valid and low cost Porro-prism binoculars, than very cheap Roof prisms binoculars.
Ciao.
Vincenzo

BAK-4 said:

I think that in the case of very cheap binoculars, Porro prisms are better than Roof prisms, with regard to achieving a satisfactory overall optical quality.

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Agreed. But this does not address my point.

BAK-4 said:

Phase Coating is something very critical and it is better to buy a Roof prism binoculars with medium or high cost, to be sure to get something really good. If your budget does not allow that, then it is better to buy a valid and low cost Porro-prism binoculars, than very cheap Roof prisms binoculars.
Ciao. Vincenzo

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Again, agreed. But I already have a few pairs of porro bins. I don't need another pair. I didn't need another pair of roof bins either, but hey, since when has that stopped any of us?

spitfiretriple said:

Phase coating costs money. Yet I have some across several bins that claim to be phase coated yet are actually very cheap. I even bought a pair (I paid £40).

Now, we know that phase coating makes for a brighter image (I won't go into the physics). But that doesn't really help us determine whether a particular pair of bins has PC. It would be easy for a re-label minor brand to tell fibs on this. Or, indeed, to innocently pass on fibs from the Chinese manufacturer.

Is there a reliable way to tell?

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I found this but aside from taking it apart......

I have often said that moderately priced roof prism binoculars are the most difficult product anyone could try to make. The constraints of the design can not really be effectively overcome except by very costly manufacturing techniques and materials. Particularly, no roof prism binoculars without phase coating are going to equal the performance of porroprism glasses often selling for quite a bit less. Still, given the marketing appeal of the roof prism design, people will try. L&S;have actually done pretty well. By using full multicoating they have minimized the drawbacks of the design, and they have been able to build in quite a number of positive features. Both binoculars are attractively rubber armored in black, employ internal center focusing, are water-resistant, and fully multicoated. Both are also quite light weight and compact, with the 10X42s being exceptional for their class. At this price point you can't expect phase coated prisms, and the lack of phase coating is evident, both in the field and on the bench.

Both binoculars have the same tested resolution at 4.7 arc seconds. That is a respectable performance without coming close to the best of the competition. Neither have particularly good image quality (test bars are fuzzy even at maximum resolution). It is the lack of image quality that effects their field performance more than resolution. The 10X42s have quite respectable scores in both the Color Extinction and Twilight Resolution tests. The 8X32s don't fair very well in either test.

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source: http://www.betterviewdesired.com/Roof-Prism-Binoculars.php

Hi,
a simple test for phase coating has been recently discussed in a German optics forum (http://www.juelich-bonn.com/jForum/read.php?9,267166,320904#msg-320904)

I did not think too much about it and also do not understand much of the matter, so can't say if this test makes sense or not. Sure there are others here who can do that better than me. So I try just to give a short summary:

Look through the objective side of the Binocular at a TFT-monitor, then hold a polarisation filter in front of the objective, turn filter and binocular until you see the roof edge vertically, then turn the filter back and forth. If there is phase coating the colour you see should change when turning the filter, if there is no phase coating, there should be only a change form light to dark, no colour change.

Florian

spitfiretriple said:

Phase coating costs money. Yet I have some across several bins that claim to be phase coated yet are actually very cheap. I even bought a pair (I paid £40).

Now, we know that phase coating makes for a brighter image (I won't go into the physics). But that doesn't really help us determine whether a particular pair of bins has PC. It would be easy for a re-label minor brand to tell fibs on this. Or, indeed, to innocently pass on fibs from the Chinese manufacturer.

Is there a reliable way to tell?

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Hold the binocular approximately 14 inches away from your eyes and look through the objective lenses. A roof prism binocular which has not been phase coated will show what appears to be a thin black line diagonally across the image of each lens. This line is not visible when the prisms have been phase coated.

@Chartwell:

On the bins in question "From the same production line as the Swift Reliant 9x27", I can just about make out a very faint (not black) line through one of the tubes - but if I blink, it's gone. Despite trying hard, and looking for it at a different angle, I can't yet see such a line in the other tube.

I tried the same test on a pair of really-really-cheap roofs, which didn't claim phase coating, and I could make out faint black lines in each tube. One line was at ten past eight, the other at ten to four - so they weren't perpendicular. Don't yet know if that's significant.

An easy test, then, and not involving screens and polarising filters, but not necessarily a conclusive one?

The tests continue...

@dalat

Interesting. Very interesting

Here's the Google translation of the German post, though dalat/Florian puts it more simply!

But, perhaps - Proposal for an experiment on phase correction coating
Posted by: saved confocal (IP)
Date: 17 February 2010 13:45

provided you have a TFT monitor and a circular or linear polarizing filter in your photo equipment. When a filter is missing, you now going tonight with the best wife of all the movies, and look at "avatar". The film is a bit got very cheesy, but the 3D effects are fun, and so is the whole fun. At the box office you get for a dollar a polarizing glasses if you do not feel like the movie, put the glasses out so maybe. The bracket removed, you look through the glasses on the opposite TFT monitor, so as that the actual sight of the side facing the films are now the monitor is facing you. Now when you rotate the lens around the optical axis, you see how the linearly polarized light of the TFT as a switch, and disappears. Now you have between glasses and TFT her binoculars, also vice versa, so that they look through the lens and behind the lens at the monitor. Twist glasses and glass, they will eventually see the roof, which they orient perpendicular. Then they turn on the filter membrane and observe what happens. Make the relatively Minox and the other with her sweetheart, so that you have. The phase-glasses then show them in turning such a color change at some point, my Nikon from blue to yellow. This color change is the effect of the phase shifter covering. An uncorrected glass should show no color change, but a significant difference from light to dark.

Sorry for the brief style, no time.

Have fun

As luck would have it, I have a pair of polarised glasses left over from watching Avatar. So, it's experiment time

Leaving the binoculars in their pouch for the moment:
If I wear the Avatar glasses, and look at my flat-screen, and tilt my head, the only thing that happens is that colours on the screen appear warmest with my head tilted 10° to the left. Same effect if I close either eye. Colours appear coldest if I tilt my head fully to either side. The same was true if I turned the glasses upside down (tricky with my nose)
I was surprised that the view through both eyes/lenses was the same; I was expecting one eye/lens to go dark at one point. Hmm.

Maybe the Avatar polarised glasses are not linearly-polarised. Maybe they are circularly polarised? Just checked wiki: it would seem they are indeed circularly polarised. NB, I didn't follow much of what wiki had to say!

Now I orient the glasses back-to-front, as it it were the screen wearing them not me. If I tilt my head (and the glasses with it) 80° to the right, everything goes dark. Black in fact. Both eyes. Same if I tilt my head 100° to the left (bit of a contortion this!)

Now let's get out my Are-they-really-phase-coated-for-£40 "Adler"? binoculars. Note: for virtually all this experiment, except where mentioned (once), I kept the bins horizontal, moving only the Avatar glasses.

I hold the bins about 10" from my eyes, but "back-to-front" - everything looks small through them(!) Holding my head and the bins steady, if I then position the Avatar glasses (conventionally oriented) between the bins and the screen and turn them left or right, I get the same result as I did without the bins. If on the other hand I hold the glasses back-to-front, I get the same both-eye "blackout" at the same angle(s) as when I did the no-bins experiment.

So far so good, but we haven't yet thrown any light on our phase-coating question.

I've just noticed: I haven't properly followed dalat's instructions yet, because he held the glasses between his eyes and the bins whereas I held them between the bins and the screen. I'll leave my mistake in place, it helps flesh out the experiment. But now I'll do as he says...

Hmm. Most intriguing. I get a sort of split image through each binocular tube. Each tube-view is split by a diagonal line The diagonal split of the left tube is at "five past seven". The diagonal split on the right tube is at "ten to four". So they are at right angles. I don't know if this is significant.

But there's a big difference in what I see depending on which way the Avatar glasses oriented. With the Avatar glasses conventionally oriented, there is a pronounced blue tinge on one side of the diagonal line, a pronounced orangey-yellow tinge on the other. As I now turned the Avatar glasses, the intensity of the blue/orange changed. At one point, there was no blue/orange demarcation, it was all just white. Well, more an off-white. But if I then kept turning the Avatar glasses, after 90° the colours gradually came back - but on opposite sides of the split line compared to when I started!

Aha! Maybe I do have a pair of genuinely phase coated bins for £40!

I kept turning the Avatar glasses. After a total of 180° of turn, the colours were back where they were when I started. After a total of 270° the colours again flipped.

I then tried obeying dalat's translation of the German advice to make the line vertical, but it seemed to achieve nothing useful. It merely gave me one more thing to think about, and made the bins harder to hold. So I didn't try moving the bins again, I kept them horizontal.
Edit: I will return to dalat's "make the line vertical..."

I then flipped the Avatar Glasses back-to-front. When I re-did the above experiment, the opposite sites of the diagonal line no longer flipped from blue to orange, they flipped from white to black. With a brief bit of grey before the black kicked in.

Next post: Let's try the same test on some really-really-cheap roofs, which we can safely assume have no phase coating. Let's see if they behave differently.

spitfiretriple;1741307 On the bins in question said:

just [/I]about make out a very faint (not black) line through one of the tubes - but if I blink, it's gone. Despite trying hard, and looking for it at a different angle, I can't yet see such a line in the other tube.

I tried the same test on a really really cheap pair of roofs, which didn't claim phase coating, and I could just about make out faint black lines in each tube. One line was at ten past eight, the other at ten to four - so they weren't perpendicular. Don't yet know if that's significant, I suspect it might be.

An easy test, then, and not involving screens and polarising filters, but not necessarily a conclusive one?

The tests continue...

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I think if you can see lines, however faint, the binocular is not phase coated. A quick look at Leica, Zeiss (schmidt-pechan prism) and Zen-Ray ED from various anles does not show these lines. Your description of the orientation for the lines BTW is correct in my experience.

Hi, sorry, maybe I should have done a bit more detailed translation work, before making you play so much

Ok, just to clarify: I did not try that myself, I also do not understand much about polarisation filters and phase coatings. All I did was summarizing the post on the German forum. Maybe I omitted a few things that are actually important?

So in the original post, the guy tells to look through the avatar glasses the wrong way. Also the turning of the glass should probably be more like a 360° turn than just turning back and forth, as I wrote in the brief summary. Hope that helps, good luck!

Florian

Don't worry about it dalat, you set me on an experimental road which I am rather enjoying and I think I'm learning quite a bit.

@chartwell: I'm not sure I'm ready to agree with you yet, you see when I tried the same test on my really-really-cheap roofs, I got a rather different result.....

With the Avatar glasses conventionally oriented, I now looked to see what image of the screen I could get through the wrong end of the really-really-cheap roofs. I saw a diagonal split-line. But whereas with the Are-they-really-phase-coated-for-£40? roofs the line was blue one side, orange the other, with these really-really-cheap roofs I now had blue one side and.... just an off-white the other. As I started to turn these bins through 90°, the blue gradually changed to orange, while the off-white side stayed off-white.

So the blue and the orange did not swap sides

I think this is conclusive. I didn't fully understand dalat's post, nor did I understand much at all of the Google translation of the original German post. But now that I have these experimental results, I think I can see what they were getting at, and it all seems to make sense.

And I appear to have a pair of genuinely phase coated bins for £40. (And of course a pair of really-really-cheap non-phase-coated bins, but I rather knew that all along).

One other test on the really-really-cheap roofs: I flipped the Avatar glasses back-to-front. They exhibited the same white/black flipping tendency I had experienced with the original roofs.

Final thought: I went back and re-did the experiments. I am no longer quite so sure that the really-really-cheap roofs kept one side of the line off-white. Sometimes it seemed slightly blue or slightly orange. Could it be that results might be less than cut-and-dried? Maybe some phase coatings are better than others?

It would be interesting if someone with some much more expensive roofs that can be assumed to be genuinely phase-coated (and with a quality coating too) could replicate this experiment.

You'll need a polarised lens or two of course, but if you don't have any and if Avatar is still showing at your local cinema, you'll never get a better excuse to go and watch it :t:

Just tried the same experiment with a pair of porros. I didn't expect to see a diagonal line (or any line) and I didn't. When I turned the glasses however (oriented back-to-front), at one angle the whole view went black. Sort-of.

chartwell99 said:

Hold the binocular approximately 14 inches away from your eyes and look through the objective lenses. A roof prism binocular which has not been phase coated will show what appears to be a thin black line diagonally across the image of each lens. This line is not visible when the prisms have been phase coated.

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I tried this with Nikon pocket roofs. The line is there, and diagonal, but goes only about 5% across, near the middle.

chartwell99 said:

Hold the binocular approximately 14 inches away from your eyes and look through the objective lenses. A roof prism binocular which has not been phase coated will show what appears to be a thin black line diagonally across the image of each lens. This line is not visible when the prisms have been phase coated.

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chartwell99 said:

I think if you can see lines, however faint, the binocular is not phase coated. A quick look at Leica, Zeiss (schmidt-pechan prism) and Zen-Ray ED from various anles does not show these lines. Your description of the orientation for the lines BTW is correct in my experience.

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This doesn't indicate the lack or presence of phase coating but the sharpness of the roof edge of the prism.

You are seen a correlation (not causations) between cheaper/older non-phase coated bins with less sharp (i.e. less precisely made) roof prisms and more recent higher quality (sharper roofs) phase coated bins.

You can check for phase coating with cross polarizers (at the objective and the eyepiece) rotating the one relative to theother. The easiest way to do this is to view the bins through polarizing sunglasses and hold another polarizer at the objective and rotate it. Or view through the objective end.

http://birdforum.net/showthread.php?t=145967&highlight=polarizer

More about phase correction here

http://birdforum.net/showthread.php?t=124362&highlight=polarized

And if you've never tried using roofs with polarized sunglasses its worth a try

http://birdforum.net/showthread.php?t=40690&highlight=polarized

spitfiretriple said:

Just tried the same experiment with a pair of porros. I didn't expect to see a diagonal line (or any line) and I didn't. When I turned the glasses however (oriented as if worn by the screen), at one angle the whole view went black. Sort-of.

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The light out from a porro is polarized in one direction across the whole field (because reflection polarizes light). But as they don't recombine two beams with different paths in one prism there are no interfence effects.

The wikipedia entry is also informative (I wrote most of it ).

http://en.wikipedia.org/wiki/Schmidt-Pechan_prism

spitfiretriple said:

One other test on the really really cheap roofs: I flipped the Avatar glasses so that they re oriented as if the screen were wearing them. They exhibited the same white/black flipping tendancy I had experienced with the original roofs.

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That's the orientation that results in the most conclusive test using a computer screen. The complete blacking out of one then the other roof face as you rotate the filter or the binocular (provided you're looking through the filter from the correct side) means no phase correction. The photo below shows a cheap roof prism monocular with no phase coating as viewed through "Avatar" glasses held backwards.

Kevin Purcell said:

This doesn't indicate the lack or presence of phase coating but the sharpness of the roof edge of the prism.

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This makes sense to me, and would explain why I can (just) see a very very faint line in one tube of my I-now-think-these-really-are-phase-coated-for-£40 roofs, but not on the other tube: One of the roof prisms is very slightly better made than the other. On my really-really-cheap roofs, the lines are more easily discerned, and in both tubes.

Kevin Purcell said:

You are seeing a correlation (not causations) between cheaper/older non-phase coated bins with less sharp (i.e. less precisely made) roof prisms and more recent higher quality (sharper roofs) phase coated bins.

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I can see the logic in this. Cum hoc ergo propter hoc.

As regards the rest, I don't have polarised sunglasses, I only have the Avatar glasses. The polarising may be different (linear vs circular)

Well done for the Schmidt-Pechan wiki though. I have read it several times in the past, it's where I learned what a SP prism was. One query I'd raise is to do with the illustration (it may not be by you):

The illustration appears to show the light beam bouncing five times. Should it not be six times? Does the light beam not bounce off both sides of the roof? I recognise it may be rather difficult to portray a 3d action in a 2d illustration. The issue does appear to be addressed in the text, to an extent at least, though I for one didn't find the discrepancy easy to grasp on first reading.

On re-reading the Schmidt-Pechan wiki, I note the statement, "...suppressed by multilayer phase-correction coatings applied to one of the roof surfaces..." (My emphasis) Ah! I had previously had it in my head that both sides of each roof were coated. I must now go back and re-think a few things.

Something else I've just tried: Stand in front of a mirror wearing your avatar glasses. Close your right eye. The lens over your left eye goes black in the mirror. Now open your right eye and close your left eye. The effect is reversed. Well, I suppose that's predictable, but it does give me a bit more to think about.

And now I've tried wearing the Avatar glasses and looking at my screen and tilting my head. Over the course of 90° I get a change from a warm screen to a cold screen. Now I flip the glasses back to front. I get no colour shift but... the screen goes from white to grey to (at 90°) completely black.

Something else I've learned: Avatar glasses use the RealD method. RealD requires a silver screen to minimise loss of polarisation. A comparison of other modern 3d cinema methods. Older systems used either coloured filters or pure-linear polarisation. Non-cinema (ie home) systems are looking to use a more expensive, more bulky pair of glasses, the lenses of which swapping rapidly between black and clear, synchronised with the screen.

And another thing (it appears there is much more to this business than originally met my eye): I've just read that the circular polarising lenses used by RealD (and others) are not pure circular; in addition to their circular filter (twisted one way - anti-clockwise(?) - on the right eye, clockwise(?) on the left) they also have a linear filter. . Otherwise, since a circular filter remains unaffected by turning, we wouldn't get our colour-changing effect experienced when turning the lens. Not sure whether the linear filters are at right angles to one another. I did think they would be, but then considered the fact that when I looked at the screen wearing the glasses and tilted my head, the screen went black in both eyes simultaneously. This informative thread suggests the linear filters are closer to your eyes. This is related to the fact that the glasses behave differently when flipped.

henry link said:

That's the orientation that results in the most conclusive test using a computer screen. The complete blacking out of one then the other roof face as you rotate the filter or the binocular (provided you're looking through the filter from the correct side) means no phase correction. The photo below shows a cheap roof prism monocular with no phase coating as viewed through "Avatar" glasses held backwards.

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So that means my £40 PCs aren't actually PCs after all?

(Please confirm for me Henry, I think I know the answer from your post, I just wanted to be 100% sure)

I'm afraid they're either not phase-coated at all or the effort at phase coating is so feeble that it doesn't accomplish anything. it might be interesting to try this test on other inexpensive roofs that claim phase correction. It could be that many of them have ineffective or only partly effective coatings.

Thanks Henry (he says, cursing under his breath)

I'll echo Henry's encouragement for anyone else to have a go at this, and I'd add: try it with your cheaper (non-PC) roofs too.

Note:
I found that the angle at which you arrange the bins, glasses and yourself is quite important; it's easy to let small misalignments creep in, which combine to corrupt the "experiment". Corruptions can include distorting the strength of colours and changing off-white areas to mixed watery blue or watery orange. Conclusion: misalignments invalidate test results.

To minimise this, I built a rig earlier to maximise consistency between tests. Okay okay, it was just a shoebox in front of the screen covered in a dark fabric to reduce distractions. I also draped a dark cloth behind the screen, and over the bits of the screen not putting light into the bins. I had hoped this would allow me to take photos, but my efforts were rubbish and I've deleted them. Henry managed far better.

I tested a third set of roofs: Audubon Vector 10x42. This cost more, even second hand, than either of the other two bins I tested earlier. It seems good quality, for example there is much less reflection from both the prism and the objective than is the case with the really-really-cheap. But the Vector doesn't claim to be PC. I won't go into all the test ins and outs, but...
The Vector demonstrated much stronger colours than the really-really-cheap; its blue was a deep violet, its orange a strong orange-bronze. Apart from this colour strength though, it behaved in essentially the same way as the really-really-cheaps in response to all the tests.

Finally, I re-tested (again) the Adler-"PC". On one test, it again behaved differently from the other two (non-PC-claiming) pairs. It did one thing the other bins definitely didn't: When the conventionally-oriented glasses were turned through 90°, the Adler-"PC" didn't just change the colour, it also flipped the colour across the line.

Maybe this indicates a feeble attempt at phase correction?
But I'm still stuck with Henry's

henry link said:

That's the orientation that results in the most conclusive test using a computer screen. The complete blacking out of one then the other roof face as you rotate the filter or the binocular (provided you're looking through the filter from the correct side) means no phase correction.

Click to expand...

Finally, I re-tested (again) the Adler-"PC". On one test, it again behaved differently from the other two (non-PC-claiming) pairs. It did one thing the other bins definitely didn't: When the conventionally-oriented glasses were turned through 90°, the Adler-"PC" didn't just change the colour, it also flipped the colour across the line.

Click to expand...

I just tried this as you describe and see the same results.

I find it easier to wear my brown-tinted vertically polarized sunglasses (fixing them with polarization vertical) and a fixed 21" LCD display as a source of vertically polarized light then rotate the binoculars as I look through the objective end. Note some screens have the polarizers at 45 degrees (this one is sunglasses compatible!).

non-PC coated bin (Promaster 7x32): shows a change of intensity (faster than linear with the position of the bin (I suspect this is ture in both cases but the PC smoothes it out) with no color. Just "clear" to "black" four times as the bin is rotated 360 degrees.

PC coated bin (Zen ED2 7x36): the gradual change in intensity and moves between different colors (reddish and yellow green at each end ... and one can see greenish in the middle) on each side of the prism's roof. The Hawke ED 8x43 is very similar.

A Zeiss 8x32FL does show the colors but darkening and brightening is much less pronounced with rotation. And the colors are much less vivid. Hmmm, a difference in type of phase coatings and perhaps PC effectiveness?

A Zeiss 8x40 Victory (with AK prisms) is very similar to the 8x32FL.

A Pentax WP 8x32 (the first Pentax roofs with PC) doesn't show the colors (strongly enough for me to really see them) but does have some darkening but not as much as the non-PC bin. At 45 degrees the screen still shows some visibility.

A Pentax SP 8x32 (the next generation of PC, I presume) shows a more pronounced lightening and darkening effect and with the roof edge at 45 degrees (across a diagonal of the screen) the screen is full darkened on both sides of the roof edge. Odd.

An Pentax 8x36 HS shows the colors (bluish to orangy-yellow) more clearly and doesn't darken the screen at 45 degrees.

A Swift Eaglet 7x36 shows the colors very clearly (with a range from very reddish-pink through greens and yellows to cyan. The range of dark to light is more than the Zeiss and the Pentax.

The polarization varies with wavelength. The reddish and greenish-yellow are most common but I can also see a light blue just as the color "jumps"). The half opposite to the greenish yellow does show bluish for a small part of the rotation. So there is compensation all across the spectrum but perhaps there is a bias to the red/green (where most of the light is).

Clearly this is quite complicated and shows some differences in the ways the manufacturers design their phase coatings. Given the Zeiss behavior I'd assume that minimal color variations and minimal changes in brightness are the best PC coatings. And the no PC coatings gives very large ranges of intensity change (and no color differences). And the others are somewhere in-between.