ENTRANCE PUPIL Meaning and
Definition
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The term "entrance pupil" refers to a key concept in optics, specifically in the field of photography and lens design. It is defined as the apparent aperture of a lens system as seen through the front element of the lens. In other words, it is the image of the physical aperture formed by the lens when viewed from the object side.
The entrance pupil plays a crucial role in determining various optical parameters and settings, such as the depth of field, focal length, and effective aperture. It serves as a reference point for the calculation of these parameters.
When a lens system is focused at different distances, the location and size of the entrance pupil changes accordingly. As the lens is focused closer, the entrance pupil appears larger and moves closer to the front element, while at greater distances it appears smaller and moves closer to the back element. This variation in the entrance pupil affects the overall optical performance of the lens.
Understanding the entrance pupil is particularly important in photography as it directly relates to the amount of light entering the lens and consequently affects the exposure and image quality. It influences the intensity and distribution of light, which in turn determines the resultant image characteristics, such as brightness, vignetting, and overall sharpness.
In summary, the entrance pupil refers to the apparent aperture of a lens system when viewed from the object side, playing a crucial role in determining key optical parameters and ultimately influencing the performance and characteristics of the resulting image.
Etymology of ENTRANCE PUPIL
The term "entrance pupil" is formed by combining two words: "entrance" and "pupil".
The word "entrance" comes from the Middle English word "entraunce", which is derived from the Old French word "entrance" and the Latin word "intrantia". Ultimately, it can be traced back to the Latin word "intrare", meaning "to enter". In the context of optics, "entrance" refers to the point at which light enters an optical system or instrument.
The word "pupil" has its roots in the Latin word "pupillus", meaning "ward" or "minor". It originally referred to the dark circular opening in the center of the iris of the eye. In the context of optics, the term "pupil" is used to describe the aperture or opening through which light enters before being focused by the lens system.
