What is the meaning of the word 'photography'

Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either chemically by means of a light-sensitive material such as photographic film, or electronically by means of an image sensor.Typically, a lens is used to focus the light reflected or emitted from objects into a real image on the light-sensitive surface inside a camera during a timed exposure. The result in an electronic image sensor is an electrical charge at each pixel, which is electronically processed and stored in a digital image file for subsequent display or processing. 

 The result in a photographic emulsion is an invisible latent image, which is later chemically developed into a visible image, either negative or positive depending on the purpose of the photographic material and the method of processing. A negative image on film is traditionally used to photographically create a positive image on a paper base, known as a print, either by using an enlarger or by contact printing.
Photography has many uses for business, science, manufacturing (e.g. photolithography), art, and recreational purposes.

Diaphragm (optics)

In optics, a diaphragm is a thin opaque structure with an opening (aperture) at its center. The role of the diaphragm is to stop the passage of light, except for the light passing through the aperture. Thus it is also called a stop (an aperture stop, if it limits the brightness of light reaching the focal plane, or a field stop or flare stop for other uses of diaphragms in lenses). The diaphragm is placed in the light path of a lens or objective, and the size of the aperture regulates the amount of light that passes through the lens. The centre of the diaphragm's aperture coincides with the optical axis of the lens system.

Most modern cameras use a type of adjustable diaphragm known as an iris diaphragm, and often referred to simply as an iris.

See the articles on aperture and f-number for the photographic effect and system of quantification of varying the opening in the diaphragm.

THERE IS ONE GOOD QUESTION

"Only the print contains the artist's meaning and message."

Examples_-_The_Making_of_40_Photographs, _1983 "> Ansel Adams, Introduction to Examples - The Making of 40 Photographs, 1983

The term comes from the Greek word phos, photos - light and graphos - writing. The word photography means writing with light but most photographers claim they are painting with light!

As far as can be ascertained, it was Sir John Herschel in a lecture before the Royal Society of London, on March 14, 1839 who made the word "photography" known to the world. But in an article published on February 25 of the same year in a German newspaper called the Vossische Zeitung, Johann von Maedler, a Berlin astronomer, had used the word photography already.The word photography derives from the Greek(PHOTOS), genitive of (PHOS), "light" and (GRAPHE) "representation by means of lines" or "drawing", together meaning "drawing with light".