The differences between ED glass and an ordinary lens

Chromatic aberration is caused by a difference in light wavelength. The focal point or magnification of a lens varies according to the wavelength of each type of incident light.
Therefore, if you look at an image through a lens with chromatic aberration, color fringing may occur.
Because a single lens cannot compensate for chromatic aberration, two lenses of different optical characteristics are combined to correct this aberration. Nikon's original ED (Extra-low Dispersion) glass lenses effectively compensate for color fringing especially at high magnification.
When observing white subjects such as swans or white eagles with an ordinary lens, a chromatic aberration is prominent at the border of the background and white part of the bird.
When you use a Fieldscope for observation or digiscoping where you need natural color reproduction, a Fieldscope employing ED glass is recommended.

Visible light is composed of lights of various wavelengths. Gathering up all of these lights to a point is ideal for objective lenses.
With a single lens, because light is bent in the same way as with a prism, the focal lengths of lights with different wavelengths vary. As a result, not all light rays reach the same point, which causes chromatic aberration.
An achromatic lens made with conventional glass materials can match focal lengths of two different wavelengths. For red and blue colors, for example, that contain both ends of the wavelengths of visible light, chromatic aberration can be reduced to a certain extent by conforming their focal lengths. However, with more detailed examination, because light with other wavelengths such as green has different focal lengths, residual chromatic aberration results. This residual chromatic aberration is known as secondary spectrum.
Combinations of conventional glasses cannot solve this secondary spectrum problem, but particular optical materials which have a unique characteristic of dispersion are needed.
ED (Extra-low Dispersion) glass has this unique characteristic and when combined with other glasses minimizes the effects of the secondary spectrum. Comparing to achromatic lenses, ED glass reduces chromatic aberration to a remarkable degree.

Description:

Features:

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  • ED Prime Extra-Low Dispersion glass

• Light high density nylon engineering plastics for lightness

• New electroless silver plating process for Refraction surface of prism,Never aging.

• Durable and Protective, Rubber-armored for shockproof and skidproof

• BAK4,FMC, Dielectric Film, Phase Film for 88% transmission and brightness

• The cooperation of different coating for viewing real color

• Long exit pupil for clear viewing even with a pair of glasses

• Nitrogen filled and O-ring sealed for Waterproof/Fogproo

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WHAT IS PHASE COATINGS

An optical technique used with roof prism binoculars to increase color fidelity.

 

Due to a roof prism's optical design, the light entering a binocular's image-erecting roof prism is split in two.

 

The two halves travel through the prism independently and are rejoined before entering the eyepiece. Because the two light paths are slightly different lengths, one half of the light takes a little longer to travel through the prism than the other. When the two halves of the image are rejoined, the longer light path half is slightly out of phase with the light that took the shorter route. This can reinforce some colors of light and cancel out others, affecting the color balance and fidelity.

HOW DOES THE PHASE COATINGS WORK?

 

Phase correcting coatings are optical coatings that are applied to one surface of the shorter light path half of the prism. The coating slightly slows down the short light path half of the incoming light that passes through that surface, causing it to once again be in phase with the light that traveled the longer path when they halves are rejoined.

 

With phase-corrected prisms, no colors are reinforced or cancelled, giving a more accurate color reproduction. The effect is particularly visible when looking sunward at a back-lit or silhouetted bird, where more color and detail can clearly be seen in the shadowed areas of the bird.

Specifications:

Magnification: 12x

 Object lens(mm): 42

Eyepiece(mm):20

 Prism System: Roof

 Prism Glass: BaK4

 Focus System: Center

 Field Of View(ft/1000yds): 241

 Close Focus Distance(m): 2.9

 Exit Pupil(mm): 3.5

 Eye Relief(mm): 14.8

 Eyecup Type: Twist-up

 Resolution: ≤4.1''

 Fog proof: Yes

 Water proof: 1.5m/3min

Argon Filled: Yes

 Phase coated: Yes

 Coating: Full Multi-Coated

 Net Weight, g: 586

Size: 143 x 127 x 52mm

Packaging details:

1x 12x42 Binocular;

1x soft carrying case,

1xcleaning cloth.