Minox ASPH BROCHURE

INNOVATIONS
IN BINOCULAR DESIGN

H

OW DO

A

SPHERICAL

L

ENSES WORK IN

B

INOCULARS

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Graphic 1 Graphic 2

For decades, aspherical lenses have been
used in cameras.These lenses are known to
significantly increases optical performance
in marginal ranges, particularly for high light
transmission wide-angle lenses. However,
because the manufacturing process for as­pherical lenses is very costly and time-con­suming, their positive effect on the image
often results in a higher price.

What benefits do aspherical lenses
offer in the lens system of high power
binoculars ?

The exterior surfaces of a normal spherical
lens are equally curved segments of a sphe­rical surface (Latin. sphaera = sphere).When
light rays strike a spherical lens, they are re­fracted towards the optical axis,which then
combines them behind the lens at a com­mon focal point (i.e., the image point). Ho­wever, this applies only to rays hitting the
lens relatively close to the optical axis. Light

rays that touch the lens further away from
the optical axis, split before this conventio­nal image point.These rays produce irradia­tion at the image point, resulting in blurred
images.This effect increases with rays at the
margin of the field of vision (see graphic 1).
To compensate for this image deterioration,
several lenses with a different configuration
and the opposite optical effect are combi­ned in an optical system (eyepiece or lens).
For binoculars, however, this means a larger
design, a loss of light transmission and hig­her weight.
Superior results can be achieved with as­pherical lenses. The curve of the aspherical
lens surface is adjusted to the margin. This
adjustment in surface curvature deflects
even light rays striking the lens in the mar­ginal ranges precisely towards the conven­tional image points.Thanks to the improved
combination of rays, a significantly sharper,
higher-contrast and, therefore, more detai-

led image is achieved over the entire image
field, including distant brush discharge and
image points away from the center of the
image.
Besides producing significantly better ima­ges, binoculars equipped with high-quality
aspherical lenses in the eyepieces, such as
the MINOX 10 x 52 asph. (Aspherical Lens
Technology), are designed with fewer and
thinner eyepiece lenses. The benefit for the
user is a shorter length and significant
reduction in weight. In addition, the image
field is consistently smooth to the margin
(see graphic 2), eliminating the need to
refocus on objects in the marginal range.
This is particularly advantageous in poor
light situations where high optical perfor­mance is achieved with fewer lenses, redu­cing reflections and significantly increasing
light transmission.
These attributes are a hallmark of the design
of high performance binoculars.

Path of rays through a spherical lens.

Path of rays through an aspherical lens – even the
marginal rays are focused on a single focal point.

Path of rays through a spherical lens.

Path of rays through an aspherical lens – the field of view
is on one level.