page_title: Exposure value
section_title: Setting EV on a camera
hierarchical_section_title: Exposure value / Setting EV on a camera
caption_attribution_description: English: Detail of front of Kodak Retina Ib 35mm camera showing the EV (Exposure Value) setting ring that couples aperture and shutter speed settings.
context_page_description: In photography, exposure value is a number that represents a combination of a camera's shutter speed and f-number, such that all combinations that yield the same exposure have the same EV. Exposure value is also used to indicate an interval on the photographic exposure scale, with a difference of 1 EV corresponding to a standard power-of-2 exposure step, commonly referred to as a stop.
  The EV concept was developed by the German shutter manufacturer Friedrich Deckel in the 1950s. Its intent was to simplify choosing among equivalent camera exposure settings by replacing combinations of shutter speed and f-number with a single number.
  On some lenses with leaf shutters, the process was further simplified by allowing the shutter and aperture controls to be linked such that, when one was changed, the other was automatically adjusted to maintain the same exposure. This was especially helpful to beginners with limited understanding of the effects of shutter speed and aperture and the relationship between them.
context_section_description: On most cameras, there is no direct way to transfer an EV to camera settings; however, a few cameras, such as some Voigtländer and Braun models or the Kodak Pony II shown in the photo, allowed direct setting of exposure value.
  Some medium-format cameras from Rollei (Rolleiflex, Rolleicord models) and Hasselblad allowed EV to be set on the lenses. The set EV could be locked, coupling shutter and aperture settings, such that adjusting either the shutter speed or aperture made a corresponding adjustment in the other to maintain a constant exposure (Ray 2000, 318). On some lenses the locking was optional, so that the photographer could choose the preferred method of working depending on the situation. Use of EV on some meters and cameras is discussed briefly by Adams (1981, 39). He notes that, in some cases, the EV indication from the meter may need to be adjusted for film speed.
caption: Detail of front of Kodak Retina Ib 35mm camera (c. 1954) showing the EV  setting ring that couples aperture and shutter speed settings.
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