What is Bushnell PC-3 Phase Coating
Would you please tell me exactly what "type" of coating that is. Is it dielectric or metal? If metal, is it aluminum or silver?
The Bushnell website only states a bunch of worthless marketing buzz words but no specifics.
Per Bushnell website:
"PC-3® Phase Coating Found on the best roof prism binoculars, this chemical coating is applied to the prisms to enhance resolution and contrast."
We're tailing about two different coatings on separate parts of the roof prism. Roof prisms require two coatings to be as efficient as porro prisms. Roofs require both a phase coating, in Bushnell's case, the PC3 and a mirror coating, be it aluminum, dielectric or silver.
Roof prisms split the image and then merge it back at the other end of the prism. Prior to phase coatings, the two images never merged perfectly as to the wavelengths of the light and thus lost some resolution and contrast. Phase coating was introduced in the 90s by Leica and for the first time, roof prisms were capable of the same degree of resolution as porro prisms. In those early days, only the most expensive binoculars offered phase coatings. These days it can be found on just about any roof prism over $100. Every manufacturer uses a proprietary phase coating formula and labels it as such. In Bushnell's case, it is called PC-3
Roof prisms also employ a mirror surface, something not used in a porro prism, so roof prisms have never been quite as light efficient as porro prisms. Aluminum oxide has always been the standard mirror coating used and if not specified by the manufacturer, this is what you have for the coating. Silver and more recently, dielectric coatings have improved light transmission over aluminum oxide coatings by a percent or two. Nice to have, but by no means a necessity and most people would have trouble seeing the difference. Makes for a good selling point, though.
ED is one of the elements in the objective of the binocular. it serves to reduce chromatic aberration - color fringing - and thus increase resolution and contrast. Again, we are not talking night and day, here, but that ED label also helps to sell binoculars.
My question now is: What type of mirror coating is used on the Bushnell Elite ED binocular... aluminum, silver, or dielectric? Am I correct to conclude it is aluminum since it is "not specified by the manufacturer"?
Since the Elite line have been compared to alpha binoculars ove the years and it is Bushnell's top of the line model, I would have expected a dielectric or silver mirror prism coating. There are other brands out there in the same price range with both ED glass and dielectric mirror coatings. One manufacturer's blog (that sells both metal coated and dielectric coated models) says "dielectric prism allows at least 5-7% brightness improvement over the best metallic coating". That would be a noticable difference and so lead me to want to find out more about what Bushnell is doing with their top of the line Elite.
Thanks for any additional information you can provide.
Found another website that specifies dielectric for the mirror coatings on the new Elite ED, so you're good to go.
Also, a 7% increase in brightness on the prism coating is not the same thing as a 7 % increase in overall light transmission. It's only a 7% increase on the transmission on the prism. That may or may knot be something you will notice, overall, but it sure doesn't hurt to have it.
Swarovski EL 10x42 WB List $2100 Paid new $1900 -- 27.5 oz -- 6 ¼ “ high
Bushnell Elite 10x42ED List $700 Paid new $377 -- 26.1 oz -- 5 ¾” high
Bushnell Elite open bridge 12.5x50 $1400 Paid new $750 – 29 oz -- 6 ¾” high
Join Date: Aug 2011
Location: South Pacific
All are clearly alpha binoculars. The 12.5x and the EL10x seem significantly heavier. The 12.5x is bigger and feels the heaviest. Its views have the greatest “Wow” factor. The Wow factor and magnification differences between the EL10x and 10xED on one hand and the 12.5x on the other seem very pronounced, more than the numbers would indicate. The focus knob on the 12.5x is too far back relative to its weight and balance and its diopter adjustment is the least refined. But it is terrific to look through and is very good in low light.
The Bushnells have the smoothest mechanical focusing; both are very fast. Mechanical focusing is very fine on all three. This is imperative to get fine optical focus. There is a very slight touch of graininess to the EL10x focusing mechanism, however, that the Bushnells lack. None match the Nikon HG LX for damped smoothness, however.
The 10xED is the fastest by far to find optical focus and this is important. It also feels lighter, more compact and better balanced, too. Why the minor weight differences should seem to matter so in this range is unclear to me. It has something to do with size, I suspect. The Bushnells are brighter in part because they show the EL10x has a very, very slight green/yellow cast to its views, the colors of its coatings. The difference in fov between the 10xED (6.0 degrees) and the EL10x (6.3 degrees) in negligible in use. I don’t notice it unless I look for it.
All present great views. The 10xED gets taken out the most because it is the littlest, the lightest and because it focuses the fastest optically and it too presents alpha views. At $377, it was an excellent buy I had not planned to make but could not pass up when I came across it. Typical prices now are from $420 to $460 for the 10xED and I have actually on two occasions seen 10xe2 prices higher than the 10xED prices from the same vendor. Silly. But there is some confusion out there.
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In binoculars with roof prisms the light path is split in two paths that reflect on either side of the roof prism 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. This causes the light to becomes partially polarized (due to a phenomenon called Brewster's angle). 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 vectors is called the phase shift, or the geometric phase, or the Berry phase. This interference between the two paths with different geometric phase results in a varying intensity distribution in the image reducing apparent contrast and resolution compared to a porro prism erecting system. These unwanted interference effects can be 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 an 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.
 Metallic mirror coatings
Main article: Mirror
In binoculars with Schmidt-Pechan roof prisms, mirror coatings are added to some surfaces of the roof prism because the light is incident at one of the prism's glass-air boundaries at an angle less than the critical angle so total internal reflection does not occur. Without a mirror coating most of that light would be lost. Schmidt-Pechan roof prism use aluminium mirror coating (reflectivity of 87% to 93%) or silver mirror coating (reflectivity of 95% to 98%) is used.
In older designs silver mirror coatings were used but these coatings oxidized and lost reflectivity over time in unsealed binoculars. Aluminium mirror coatings were used in later unsealed designs because it did not tarnish even though it has a lower reflectivity than silver. Modern designs use either aluminium or silver. Silver is used in modern high-quality designs which are sealed and filled with a nitrogen or argon inert atmosphere so the silver mirror coating doesn't tarnish.
Porro prism binoculars and roof prism binoculars using the Abbe-Koenig roof prism typically do not use mirror coatings because these prisms reflect with 100% reflectivity using total internal reflection in the prism.
 Dielectric mirror coatings
Main article: Dielectric mirror
Dielectric coatings are used in Schmidt-Pechan roof prism to cause the prism surfaces to act as a dielectric mirror. The non-metallic dielectric reflective coating is formed from several multilayers of alternating high and low refractive index materials deposited on the roof prism's reflective surfaces. Each single multilayer reflects a narrow band of light frequencies so several multilayers, each tuned to a different color, are required to reflect white light. This multi-multilayer coating increases reflectivity from the prism surfaces by acting as a distributed Bragg reflector. A well-designed dielectric coating can provide a reflectivity of more than 99% across the visible light spectrum. This reflectivity is much improved compared to either an aluminium mirror coating (87% to 93%) or silver mirror coating (95% to 98%).
Porro prism binoculars and roof prism binoculars using the Abbe-Koenig roof prism do not use dielectric coatings because these prisms reflect with very high reflectivity using total internal reflection in the prism rather than requiring a mirror coating."
 for Wikipedia
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Yesterday, I received an answer from Bushnell. It was a one sentence response and said ..... The engineering department said it is dielectric.