Digital Photography - Camera Sensitivity

ISO (International Standards Organization) and ASA (American Standards Association) are one and the same specification; light sensitivity device measurements (film or solid state chips (CCD, CMOS).

ISO ratings range from 25, 50, 100, 200, 400, 800, 1600, etc. These are known as "Speed and Stops" Notice how the sensitivity values double from one stop to the next, or halve if decreasing. The Stops correspond to Shutter Speed and Aperture settings (Stops).

If you increase the ISO value from 100 to 200 you have doubled the sensitivity to light striking the photo sensitive device. Just as in film photography, if you increase the sensitivity to light you increase the overall grain produced by the higher level of sensitivity.

In film photography the values of sensitivity were achieved through chemical processes during the manufacture of the film, and during the development process after exposures were made. "Push Processing" was used in the development processing to draw out more details in the under-exposed areas of a roll of exposed film.

In digital photography the sensitivity values are adjusted in the camera by applying different voltage levels to the solid state device. The increase of voltage value to the solid state device also creates electronic noise in the exposed image. This noise is commonly called Digital Noise, and can be reduced in Post Processing image software.

In film photography to change the ISO value of the film the exposed film must be re-wound into the metal canister. A new roll must be loaded into the camera. When the older roll is needed it must be loaded into the camera and advanced to one frame past the previous exposure.

In digital photography the ISO value can be changed on the fly with a simple menu change in the camera body. You could make 100 images and every other image have a different ISO value without opening the camera body.

With both mediums, film, or digital, changing the ISO may require changes in Shutter Speed and/or Aperture settings to obtain the best exposure.

Film photography can be a very expensive profession, or hobby. Digital photography can also be a very expensive business, or hobby.

Consider the cost of the cameras, lens groups, development, print development, and accessories.

Digital photography requires some additional equipment; computer to view the pictures, printer to make photo prints, and an Internet Service Provider to share your photos.

The difference between film and digital depend on what you can do with the additional equipment. With film all you can do is capture images and share paper prints with family and friends through Snail Mail. With digital you can use the computer for thousands of other tasks like taxes, letters, e-mail, sharing the photos on hundreds of photo web sites.