Camera Definitions of SLR & ISO Terms
The field of photography has a lot of acronyms such as SLR, ISO, DSLR, RAW and more. Decoding some of these terms and how they relate to the real world of photography often gets confusing. The Internet contains a lot of information on photography; some of it often misleads and confuses readers. Understanding basic photography terms helps you learn more about your camera and what it can and can't do.
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SLR Defined
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The acronym "SLR" stands for single-lens reflex. In 1861, Thomas Sutton invented the single-lens reflex camera. A single-lens reflex camera uses a single lens on the front of the camera to view and record the images. The SLR also uses a reflex-mirror inside the camera body. The mirror reflects the image captured through the lens up into a housing that transmits the image to the camera's viewfinder. The mirror also flips up during exposure to allow light to reach the film located in the camera's film compartment. Modern SLR cameras contain digital components and capture digital images, thus the term "DSLR" has worked its way into photography's vernacular.
DSLR vs. SLR
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The basic components of both DSLR and SLR camera types work the same. Both types use a single-lens to view and capture images. Both contain a reflex-mirror used to reflect the image up to the viewfinder, and both work on the same principles of exposure. The main difference between the two camera types is the media used to record images. SLRs use film, while DSLRs capture images through charge-coupled devices or complementary metal-oxide semiconductor chips and record them to digital memory.
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ISO
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ISO is not a thing; it's actually an organization -- the International Organization for Standardization. Back in the days of film photography, photographers purchased film based on its ASA number and film characteristics. The ASA number was actually one of many standards developed by the American Standards Association. The ASA number expressed the sensitivity of a given film to absorbing light. Over the years, ASA and another organization named Deutsches Institut für Normung became the International Standards Organization, now known as the International Organization for Standardization. ISO still represents how sensitive a media is -- film or digital -- to absorbing light. Higher ISO numbers are more sensitive to light than lower ISO numbers.
How ISO Works
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Since a higher ISO number is more sensitive to light than a lower ISO, the higher ISO requires less exposure to capture the same amount of light. The ISO serves as one of the three sides of the exposure triangle. Aperture and shutter speed comprise the other two sides. These three work together to create a well-exposed image. In certain situations, using a high ISO setting allows a photographer to shoot without flash, freeze movement or increase depth in an image. A low ISO setting can produce exceptionally sharp, detailed images with greater color and clarity. Low ISO films such as Kodachrome 25 and Fujichrome 50 were known for their exceptional color, clarity and resolution.
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References
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