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Film speed ASA/ISO

Sensitivity to light affects how quickly film exposes and image quality

Film speed refers to the sensitivity of film to light. In general, films with a higher sensitivity (larger number, fast) have coarser grain and do not register detail or reproduce enlargements as well as films with lower sensitivity (lower number, slow). Slower film speeds equate to better detail and sharpness in your photographs, but need to be exposed for longer than faster film speeds.

Film sensitivity is measured by a set of standards established by the American Standards Association (ASA) and the International Standards Organization (ISO). For all practical purposes, ASA and ISO numbers are interchangeable. A typical number series for film speed, from slow to fast, is:

25   50   100   200   400   800

Each stop on this scale is twice as sensitive to the number on the left, and half as sensitive as the number to the right. N.B. Remember to set the camera for the same number that is on the film to get the correct exposure readings from your light meter.

  • Rangefinder Cameras
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About Ilott Vintage

A valuable reference for anyone wanting to learn more about rangefinder cameras, manual film photography, or both, this website is intended to serve not only as a resource to discover some amazing objects but also as a place to learn more about them, to understand exactly what they are capable of, and why. Read More

See Also
  • Fujica V2 Super sharp shooter
  • Zorki 10 Soviet style
  • Minolta Hi-Matic 7s
    Minolta Hi-Matic 7/7s A feature rich classic, manual and semi-automatic shooting down to f22
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    Wednesday 22nd March 2023