Aberration

## Definition

Deviation from what is normal, right or natural. In optics, defects of a lens system that cause its image to deviate from the rules of paraxial imagery.

Abbe-Porro prism

## Definition:

A compact version of the traditional Porro image-erecting prism used in binoculars. It's a type of reflection prism used in some optical instruments to alter the orientation of an image.

## English Expression：

Abbe sine condition

## Definition:

See sine condition.

## 定义：

u´/sin U´ = u/sin U

sine condition

## Definition:

A condition, first stated by Abbe, that must be met by any spherically corrected lens if it is also to be free from coma in the neighborhood of the lens axis. Mathematically the condition is:

u´/sin U´ = u/sin U

where u, u´ are the slopes of the entering and emerging portions of a paraxial ray from object to image and U, U´ are the corresponding slopes of a marginal ray.

## English Expression：

Abbe refractometer

## Definition:

An optical instrument used to measure the index of refraction of an unknown sample of optical glass. Designed by Ernst Abbe in the early 1900s, this instrument will typically yield index accuracy of two units in the fourth decimal place.

Abbe prism

## Definition:

A particular form of roof prism that can be used to invert an image. Because of the perpendicular end faces, it can be inserted between the objective and eyepiece of a telescope. If the roof is replaced by a plane surface, it becomes a reversion, or K, prism.

## English Expression：

Abbe illumination

## Definition:

A form of illumination where the source is imaged directly onto the object being viewed or projected. This requires a source of uniform intensity, such as an arc lamp.

## 定义：

（也称V数或v数）描述一个光学介质的折射率和色散能力的比值的常数。高V数表示对所有波长的折射近似相等（棱镜的色散较小）。

$V_d = \frac{n_d - 1}{n_f - n_c}$

Abbe condenser

## Definition:

(also V-value or v-value). The constant of an optical medium that describes the ratio of its refractivity to its dispersion. A high V-value indicates more nearly equal refraction at all wavelengths (less rainbow from a prism).

$V_d = \frac{n_d - 1}{n_f - n_c}$

where $V_d$ = V-value at $\lambda$ = 588 nm, $n_f$ = index of refraction at $\lambda$ = 486 nm, $n_c$ = index of refraction at $\lambda$ = 656 nm, and $n_d$ = index of refraction at $\lambda$ = 588 nm. The reciprocal of dispersive power.

Abbe condenser

## Definition:

A two-lens combination designed by the physicist Ernst Abbe. It is located below the stage of a microscope and functions to collect light and direct it onto the object being examined. Its high numerical aperture makes it particularly suited for use with most medium- and high-magnification objectives.

## English Expression：

abaxial spherical aberration

## Definition:

A type of aberration in which a symmetrical light patch is formed at points that do not lie on the lens axis. When the image moves away from the center of the field, the patch increases in size, aiding in the formation of coma. Also known as abaxial spherical aberration.