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How big an improvement are phase coatings?

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#1 stargazer193857

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Posted 30 June 2016 - 04:56 AM

Anyone have an otherwise decent roof prism without phase coatings, maybe in the $200 price bracket? How does it compare to your $100 porro prism? Do phase coatings make that noticeable a difference to the non-expert eye?

 

I bet the lens coatings on my porro are better than those on my roof, making it a non-even comparison.

 

 

I assume the coatings cost more than silver. The silver is actually cheap. It is the chemicals and environmental rules that add cost. Silver or aluminum solve the phase separation, since there is something different about internal reflection vs mirror reflection ... although even water reflection gives everything the same polarity. So I don't know if I believe that.

 

I wonder what the reflectance is of silver or aluminum from inside glass, and at different angles. I suspect is is different from external reflectance that has protectors or oxidation. I read protected silver is about 98% over a broad spectrum, even though the bare metal is much worse. But those are external reflections in air.



#2 MartinPond

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Posted 30 June 2016 - 05:30 AM

A Porro prism design does not need phase coating.



#3 Pinac

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Posted 30 June 2016 - 07:36 AM

I think you are mixing up three different kinds of "coating", of which two are actually a coating, one is rather a mirror.

 

Antireflctive coatings cover the optical surfaces of lenses and prisms in modern binoculars and improve transmittance (or transmission, if you prefer), and their effect is quite substantial on image brightness. This is true for both Porro and roof prism binoculars.

 

Phase coating is only applied in roof prism binoculars to reduce the loss of contrast due to the special polarizing effect caused by the splitting and recombining of the light beam. This is NOT used in Porro binoculars. The contrast and sharpness improvement of the phase coating is more easible visible with binos of 8x, 10x and more, and less so in a 6x bino.

 

Lastly, the "coating" you seem to have in mind when you mention "silver" functions as  a mirror and is applied to the one prism surface in one of the common roof prism designs - i.e. Schmidt Pechan - at which total internal reflection is not achieved because the angle of the beam is to small. Silver is still used for this but gradually replaced with something called dielectric layer.

 

So if I look at the question in the title of your topic, my answer would be: it is substantial. Just look through a roof prism bino such as Zeiss 8x30 or a Leica Trinovid 10x40 from the 1970s and compare their images with models from the 1990s or later.


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#4 stargazer193857

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Posted 30 June 2016 - 08:18 AM

I'm now reading it improves contrast and resolution of roof prisms. by 20-30%. I think a bino would have to be mounted to notice a 30% improvement in resolution. However, contrast might be noticeable right away. I don't get how contrast is harmed by the spit in waves.

 

My goal is to make an Abbe-Konig prism 5x25 binocular. It has 100% internal reflectance everywhere, but it also has one roof prism. I want it to be hand held for constellation scanning. Splitting some doubles would be nice, but I think a 30% loss won't be noticed hand held. The contrast loss is what I'm concerned about. Why the loss? How much? It is random light scattered through the image?

 

As for the silver, yes, that was probably the reflecting surface. I thought I read that phase correction was first achieved with silver, but everywhere I read says that mirrors change the polarization.

 

 

As for 1970's vs 1990's, I think the coatings would be different too, and fresher. I'm reading that roof prisms over $100 have some form of phase coating. I wondered if anyone compared a $200 roof to a $50 roof that maybe has similar lens coatings but different roof coatings. Or better yet, a $50 roof to a $50 porro. There are surfaces that double for transmission and reflection, so that would obfuscate the measurement. According to Freznel's equations, they should not be doing a good job at either.


Edited by stargazer193857, 30 June 2016 - 08:21 AM.


#5 sg6

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Posted 30 June 2016 - 08:30 AM

Silver coatings are not phase coatings, phase would relate to the aanti-reflection on the fron and rear of a lens, not a mirror or a prism.

 

If a prism is coated it is to force reflection or simply to maintain a clean surface. Many will operate by total internal reflection so not need a silvering. However this reflection is dependant on the glass/air interface. Without a coating it surface gets dirty and you have a glass/muck/air interface and so the reflection starts to fail. So they coat the prism surface with silvering of one sort or another. It keeps it clean and it looks sensible.

 

An antireflection coating is "phase" as the depth of the material is 1/(4 * Material refractive index) (??) in depth and that causes the 2 reflected rays from the first and second surface to be 1/2 wave out of phase and destructive interferance occurs and light gets transmitted through - Yes it is all weird. Destructive interference occurs and it is not (cannot) really be destroyed but therefore passes through the lens.

 

Still not sure the bit with the refractive index is right, had it different initially but that seemed wrong - go look it up if it really is worth it. Basically the reflected waves have to be 1/2 wave out of phase, so all antireflection coatings are "Phase coatings". It is advertised as such since it sounds better and they might get people to buy the goods, without realising that all anti-reflection coating are technically "phase coatings".



#6 marktd

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Posted 30 June 2016 - 09:57 AM

If a prism is coated it is to force reflection or simply to maintain a clean surface. Many will operate by total internal reflection so not need a silvering. However this reflection is dependant on the glass/air interface. Without a coating it surface gets dirty and you have a glass/muck/air interface and so the reflection starts to fail. So they coat the prism surface with silvering of one sort or another. It keeps it clean and it looks sensible.

 

This is very confusing, and/or just wrong -- it's actually hard to tell what you're saying.  It seems like you're saying prisms are mirrored to keep them clean so the total internal reflection works.

 

But it seems you have introduced another coating type not mentioned above -- the ones to help "keep clean".  Exterior surfaces of many binoculars are coated to make them resistant to scratching, to make them repel water and oil, etc.  This is completely separate from coatings to change optical properties. 

 

To re-iterate:

 

Anti Reflection (AR) coatings -- when light strikes an optical surface, some is transmitted and some is reflected.   Uncoated glass reflects about 4% of light striking it, AR coatings reduce this to less than 1%.  This applies to (and benefits) everything -- lenses, prisms, filters, etc, except where total internal reflection (TIR) is happening.

 

Phase correcting or phase compensating coatings -- specific to roof prisms, where the light is split and re-combined which causes a polarization effect.  The phase compensating coatings shift and correct this.

 

Mirror coatings -- silvering, aluminizing, dielectric coatings, etc. seek to cause 100% reflection.  These are applied to mirrors (duh) and also to prism surfaces where the angle of incidence is below that which causes TIR.

 

Non-optical coatings -- coatings that make surfaces repel water and oil, increase hardness to resits scratches, etc.  There are applied to surfaces that are exposed to the elements.



#7 GlennLeDrew

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Posted 30 June 2016 - 01:08 PM

Partial polarization occurs always upon reflection, being most effective at an angle of incidence 60 degrees from perpendicular. Coincidentally, this is the incidence angle for each of the roof surfaces for a 90 degree Amici prism. Yet my non phase coated, single-layer AR coated Amici delivers a satisfying enough ~92% transmission, according to my not-so-precise meter. Contrast through it is fairly indistinguishable from that of a direct view. I've enjoyed views of quite dim and subtle nebulae. What losses that are introduced are to me quite unworthy of fretting over. ;)



#8 stargazer193857

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Posted 30 June 2016 - 05:57 PM

92%? Ah, because the roof prism is not completely at full internal reflection angles?

 

The Abbe-Konig has higher incidence angles than at porro prism, but lower incidence than a 90° Amici. Granted only 2 weak surfaces. A 45° Amici would transmit the most light. Lots are for sale, ready to mount lenses and eyepieces easier than an Abbe Konig.

 

Maybe I should make a 45° Amici bino. Holding it steady would be easy easier than straight through.



#9 MartinPond

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Posted 30 June 2016 - 09:53 PM

Most of a roof prism combines the light  with little trouble.

The phase-sift issue only causes trouble near the vertex, where the light crosses,

making a little diffraction effect.   The idea of "20-30%" contrast effect seems bizarre.

Seems really hyped up.



#10 Henry Link

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Posted 30 June 2016 - 10:00 PM

All of those wedge shaped "Amici" prisms are actually Schmidt prisms with four internal reflections. Why the sellers continue to call them Amicis is a mystery. A true 45º Amici would be very long with a housing shaped like the Televue 60º mirror diagonal.


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#11 stargazer193857

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Posted 30 June 2016 - 10:05 PM

I'll definitely make sure the focal point is not near a roof ridge, or even a face.



#12 marktd

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Posted 01 July 2016 - 12:05 AM

 

Maybe I should make a 45° Amici bino. Holding it steady would be easy easier than straight through.

 

See:

 

http://www.skyandtel...uiltRABinos.pdf



#13 stargazer193857

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Posted 01 July 2016 - 12:41 AM

 I read in the equipment forum that because amici prisms don't reverse the direction of the light the same as a normal roof prism, they don't need phase correction. At least no one over there has heard of such a diagonal prism.



#14 stargazer193857

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Posted 01 July 2016 - 12:55 AM

 

 

Maybe I should make a 45° Amici bino. Holding it steady would be easy easier than straight through.

 

See:

 

http://www.skyandtel...uiltRABinos.pdf

 

So that is what Glenn looks like.



#15 GlennLeDrew

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Posted 01 July 2016 - 05:28 AM

Ha! Back in my more wild-haired days, and in a stout breeze, to boot. My avatar is much more representative of my mug these days.



#16 mooreorless

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Posted 01 July 2016 - 06:21 PM

http://www.birdforum...88&postcount=19

 

Picture of non phase coated Nikon roof prism binocular and a Swarovski 8x30 SLCneu phase coated binocular. For the life of me I can not remember the name of this old Nikon roof IF binocular right now. I still have it. I hope this helps some.


Edited by mooreorless, 01 July 2016 - 06:23 PM.


#17 stargazer193857

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Posted 02 July 2016 - 03:30 AM

http://www.birdforum...88&postcount=19

 

Picture of non phase coated Nikon roof prism binocular and a Swarovski 8x30 SLCneu phase coated binocular. For the life of me I can not remember the name of this old Nikon roof IF binocular right now. I still have it. I hope this helps some.

Too bad that link only shows the one post and has no link to the thread.

 

The picture shows a huge difference in brightness. Looks like a 4x difference.

 

Hmmm... I have a 7x18 Carson $15 roof prism monocular. It sure does dim the wall, but not by nearly the margin in that picture. Of course, I'm seeing a 2.6mm exit pupil. My eyes are likely 3 or 4. I could stop down my 8x40 to 21mm. Eye placement could also be a factor.

 

If it truly does darken it 30%, I would want the flat prisms.


Edited by stargazer193857, 02 July 2016 - 03:33 AM.


#18 stargazer193857

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Posted 02 July 2016 - 03:36 AM

I did a star test with my 7x18 $15 roof prism on Vega. No matter which stars I looked with my glasses on, I could not get any of them to show double. Maybe they were too shaky to tell, holding it up so high. I'll head back out and check again laying down. Should amuse my neighbors some more.



#19 stargazer193857

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Posted 02 July 2016 - 04:32 AM

In those pictures, the left circle is the non-phase coated through a polarized filter, blacking out the one half. The right circle is the phase coated one. Why is it halfway between the brightness levels of the 2 halves of the first one?

 

I don't think that proves that any light is lost. What the thread does say is that higher priced binoculars work better than lower priced. The non-phase coated Zeiss outperformed the porroprism Nikon Action. The cammo binoculars are cheap. The Nikon SE blew away its competition. None of this points to phase coatings being better, except the comparison of the 2 Zeiss.

 

I guess I could buy a plastic erect image diagonal and plastic correct image diagonal, with no coatings, and see which one transmits more brightness. At $7 each it would be a cheap experiment. They could even be used as 1x finders. I'd also point both at a light side by side.



#20 stargazer193857

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Posted 02 July 2016 - 05:48 AM

I have a 6x25 straight through cheap finder scope, and a 7x18 roof prism monocular.

Using construction paper, I stopped the finder down to 18mm.

I got a white envelop as the simultaneous target, since I knew my eyes would just adapt to any brightness directly.

My hands blocked both from the light, giving some shade to see the light. Both were focused passed infinity a bit.

I distanced them from the paper to make the same size projection on it.

The straight through was noticeably brighter, as I expected.

However, this does not prove that phase shift reduces brightness. It can be explained by the other prism reflection losses in the uncoated 7x18.

 

My Celesteron 8x40 stopped down will be a fairer test. It has MgF2 coatings, but the prism faces might not be coated. The roof prism has aluminum too. It just is not a fair comparison no matter what I do.



#21 stargazer193857

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Posted 02 July 2016 - 06:35 AM

I'm googling around and just not finding any reliable sources to claim that phase coatings make images brighter. Any tests are apples to oranges and did not specifically say brighter.

 

Lots of people repeating what is said in ads, but they also make false claims, such as that BaK4 is clearer than BaK7, or that porro prisms have 100% internal reflection. Seems like a lot of hype out there. No well done tests.

 

If normal light is a mix, and mirrors separate the poles, and the ray trace suggests they stay separate until the retina. At that point, are they not the same mix that would have came in naturally? Unless someone shows me real proof, I think that phase coatings are just marketing hype to get you to spend more.

 

At high power on planets, the roof edge can show a diffraction spike. I'm sure expensive roofs are closer to 90 degrees by selecting the good ones from the lot. At low power looking at Vega, I did not see any spike. I'll try Mars tomorrow.



#22 Pinac

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Posted 02 July 2016 - 07:41 AM

I'm googling around and just not finding any reliable sources to claim that phase coatings make images brighter. ......

.....

Unless someone shows me real proof, I think that phase coatings are just marketing hype to get you to spend more.

.....

 

 

 

I assume that you are mostly just kidding, or do you actually believe some of things that you write ?



#23 Binojunky

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Posted 02 July 2016 - 09:40 AM

 

I'm googling around and just not finding any reliable sources to claim that phase coatings make images brighter. ......

.....

Unless someone shows me real proof, I think that phase coatings are just marketing hype to get you to spend more.

.....

 

 

 

I assume that you are mostly just kidding, or do you actually believe some of things that you write ?

 

Phase coatings, ED glass and all the other hype are only improvements if the rest of the instrument in question is a sound design, I have seen some poor examples of binoculars offering the latest and greatest in so called improvements and some older instruments lacking both that gave far better, even outstanding views,TD.



#24 Pinac

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Posted 02 July 2016 - 04:14 PM

Phase coatings, ED glass and all the other hype .....

.....

 

 

 

 

 

What other hype ?



#25 stargazer193857

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Posted 02 July 2016 - 05:28 PM

 

I'm googling around and just not finding any reliable sources to claim that phase coatings make images brighter. ......

.....

Unless someone shows me real proof, I think that phase coatings are just marketing hype to get you to spend more.

.....

 

 

 

I assume that you are mostly just kidding, or do you actually believe some of things that you write ?

 

I'm just asking for a reliable source that polarized light, recombined without correction, gets dimmer.So far all I've found is sales ads claiming it, a few articles repeating those ads and incorrectly stating stuff I know about BaK4 vs BK7 glass, and forum users describing experiments that don't seem relevant.




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