Definition

1. Noun:
   • The ratio of the focal length to the diameter of a (camera) lens system: This is a technical term in optics and photography that quantifies the light-gathering ability of a lens. A lower number indicates a larger aperture (more light entering), while a higher number indicates a smaller aperture (less light entering).

Usage

• The term "stop number" is used almost exclusively in technical contexts related to photography, cinematography, and optics. It is a precise measurement for setting exposure.
• It is commonly referred to simply as an "f-number" or "f-stop" (e.g., f/2.8, f/8, f/16). The "stop" refers to the aperture setting of a lens.

Examples

• Noun:
  • To achieve a shallow depth of field, the photographer selected a low stop number like f/1.8.
  • Increasing the stop number from f/4 to f/8 reduces the amount of light entering the camera by half.
  • The lens specification lists its maximum aperture as a stop number of f/2.0.

Advanced Usage

• "To stop down": This phrasal verb means to increase the stop number (i.e., make the aperture smaller).
  • The photographer stopped down to f/11 to ensure the entire landscape was in focus.
• "Full stop" or "one stop": Refers to a doubling or halving of the amount of light. Changing the stop number by one full stop (e.g., from f/5.6 to f/8) halves the light.
  • Closing the aperture by one stop required a slower shutter speed to compensate.

Variants and Related Words

• F-number (n): Synonymous with "stop number." The standard notation is f/N, where N is the stop number.
  • The f-number is a critical setting for exposure.
• F-stop (n): A common synonym, often used interchangeably with "stop number" or "f-number."
  • She adjusted the f-stop on her camera.
• Aperture (n): The physical opening in the lens that the stop number measures.
  • The aperture diameter is controlled by the stop number setting.

Synonyms

• F-number: The ratio of focal length to aperture diameter.
• F-stop: A setting on a lens corresponding to a specific f-number.
• Aperture value: Another term for the f-number setting.

Related Phrases

• Depth of field: The area of acceptable sharpness in an image, which is directly controlled by the stop number.
  • A high stop number (e.g., f/16) creates a large depth of field.
• Exposure triangle: The relationship between aperture (stop number), shutter speed, and ISO sensitivity.
  • Understanding the stop number is essential for mastering the exposure triangle.

Noun

1. the ratio of the focal length to the diameter of a (camera) lens system