Instrument For Calculating Photographic Exposures Watkins U.S. Patent 456869 (1891)
Book details
- Title
- Instrument For Calculating Photographic Exposures Watkins U.S. Patent 456869 (1891)
- Publication year listed
- 1891
- Format
- Public domain eBook
- Reading access
- Free online reader; no registration required
- Source record
- View on Archive.org
About this book
Instrument For Calculating Photographic Exposures Watkins U.S. Patent 456869 (1891)
Author: Alfred Watkins
Year: 1891
Instrument for Calculating Photographic Exposures is Alfred Watkins's 1891 United States patent for the exposure meter that became known as the Watkins Standard Exposure Meter. The patent describes a compact instrument combining an actinometer, a pendulum timer, and a set of circular logarithmic calculating scales used to determine photographic exposures. Light intensity was measured by observing the time required for a strip of sensitized bromide paper treated with potassium nitrite to darken to a standard tint, after which the exposure could be calculated by setting scales representing actinic light intensity, plate sensitivity, subject brightness, and lens aperture. The invention represents one of the earliest practical attempts to standardize photographic exposure determination and laid the foundation for the widely adopted Watkins speed system used by photographers in the late nineteenth and early twentieth centuries.
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