Leica APO Televid 62, Brochure

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Distortion  

The term distortion is used to describe 

the effect that causes the image of an object to 

be rendered with a non-uniform reproduction ratio. 

For binocular observation, unlike in photography, 

this effect is applied quite deliberately to reduce 

the so-called “globe effect” caused by perspective

observation and by swinging the binocular. To the

observer, the image created in this manner appears

straightened out. There are two kinds of distortion :

pincushion distortion (illustrated on the top), and 

barrel distortion (as shown on the bottom). Observa-

tion through a binocular that does not have deliber-

ately implemented judicious distortion is quite un-

pleasant.

Color errors (chromatic aberrations)  

Every image-forming

component made of glass – such a lens elements – refracts

light rays of different colors at different angles. This results in

the fact that not all the light rays that emanate from a multi-

colored point on the object are re-united at a single point in

the image. This results in color errors for the observer. Color

errors become particularly evident to the observer as color

fringes when high magnifications and long focal lengths are

being used, as they are in spotting scopes. Pictorial examples :

Color errors appear primarily as color fringes around dark

objects in front of bright backgrounds, as illustrated by the

example on the left with the red-fringed feather dress. With

APO correction of Leica (right illustration) such color effects

are no longer discernible. 

Optical glasses with anomalous partial dispersion 

Light rays of different colors are refracted at different angles

through the lens elements. This effect is called dispersion and

in different types of glass it is present at different levels of

strength. Most types of glass have typical, “normal” charac-

teristics. Special glasses with “anomalous partial dispersion”,

on the other hand, have characteristics that are different in 

certain ranges of colors, and this makes a special color error

correction possible that cannot be achieved with normal types

of optical glass. Glasses with anomalous partial dispersion 

are used for the enhancement of image quality, and they are

used in all Leica binoculars and spotting scopes. 

Glossary

APO color error correction  

APO stands for apochromatic

color error correction. It is only beneficial for lenses with long

focal lengths and for high magnifications, like in spotting 

scopes. Apochromatic color correction is achieved by the use

of special types of optical glass with anomalous partial disper-

sion and with glasses that contain fluorite. Such correction

results in images with enhanced sharpness, increased contrast

and an extremely natural color rendition.

High refraction glasses  

Lens elements made of high refraction glasses bend light rays more strongly than lenses with the same

shape that are made of standard glasses. Therefore the use of a lens element made of high refraction glass can achieve strong

effect without the need for lenses with excessively strong surface curvatures. This helps to prevent imaging errors, thus leading

to greater imaging performance. High refraction optical glasses are used in all Leica binoculars and spotting scopes in order to

make their short construction possible.

ASPH.   

ASPH. is an abbreviation that denotes the use of at least one aspherical lens surface in an optical system. Unlike regular

spherical lens surfaces, aspherical lenses have a curvature near their edges that is different from the curvature in the center of

the lens. That makes it possible to influence light rays passing through the edges of the lens differently from light rays passing

through the center portion of the lens. It also makes it possible to achieve several correction goals simultaneously with only one

lens element. Furthermore it helps to reduce the weight and the physical size of an optical system and it makes certain imaging

characteristics possible to begin with. Such surfaces help to increase the image quality or to influence the distortion. The fabri-

cation and the handling of aspherical lens elements is significantly more costly, however, than that of conventional spherical 

lenses. In order to assure the extremely high image quality in all models of Ultravid binoculars, aspherical lenses are used effect-

ively in the 25 mm and 20 mm BR / BL models. In the remaining models the high image quality is achieved by means of complex

optical systems that consist of several lens elements. 

Astigmatism  

Because of the naturally curved shape of a lens, not all light rays

converge on the same plane. While the center of the picture is sharp, the edge of

the picture appears to be out of focus. One can cause objects in one or the other

plane to be rendered sharply by refocusing. In addition, astigmatism causes the

sharpness of an object detail to be influenced by its orientation. This effect becomes

stronger towards the edges of the image. For example, if we look at the corner of 

a picture of a chain link fence, it will be noticeable (if astigmatism is present) that

the wires that point towards the center of the image are reproduced with a diffe-

rent degree of sharpness than those that are oriented at a right angle to them. 

By refocusing, one or the other wire direction can be rendered sharply, but not

both of them at the same time. This effect can be reduced by appropriate optical

design measures, but it cannot be eliminated completely. Astigmatism leads to a

significant impairment of the image quality.