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Posts Tagged ‘photographic

Technical Photographic Term of the Week: Density

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Density is the opacity of a particular area of an image.  In a positive image (prints, transparencies, digital displays) a dark shadow would be said to have a high density. On a negative, bright highlights are described as having high densities. Density is sometimes used to describe the overall exposure of a particular image (IE a light image would have low density.)

Written by stevebuchanan

March 28, 2012 at 10:19 am

Photographic Term of the Week: Dynamic Range

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Dynamic range is the difference between the brightest and darkest portions of any given scene. Photographic systems have limited ability to capture dynamic ranges, therefore it is important to manage the dynamic range within a scene by manipulating lighting and/or composition.  For example… an scene lit with only sunlight on a clear day may have a dynamic range of 20 stops, which is beyond the range of currently available systems in a single exposure (multiple exposure HDR notwithstanding.) Therefore it will be necessary to alter the existing dynamic range of the scene by adding supplemental light or other methods of reducing the scenes native dynamic range – or accept the scene will have some areas that are too bright and/or too dark to be fully represented in the image.

Written by stevebuchanan

March 16, 2012 at 5:03 pm

Photographic Term of the Week: Depth of Field

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Depth of Field is the range of sharp focus within an image. Measured in distance from the focal plane, depth of field (of DOF) is affected by many factors. Key factors being…

1. Aperture (f/stop.)  The smaller the aperture (higher f/number) the greater the depth of field, or more in focus.
2. Focus Distance. The farther the primary focus distance, the greater the depth of field.
3. Focal length of lens. The shorter the lens (lower focal length) the greater the depth of field.

By manipulating these factors the photographer can adjust the depth of field to suit their needs.

Many lenses have a printed DOF scale on the lens barrel to aid the photographer in determining how deep the field of focus will be. It’s worth noting, however, that there is no agreed upon standard for what constitutes sharp focus. Therefore scales will differ from manufacturer to manufacturer. Further complicating matters is the fact that in today’s world of different digital sensors within the same platform of lens mounts, a DOF that may have been acceptable with one camera body, may not be on another higher resolution body. Nonetheless, the optical principals of DOF remain the same across all lenses.

Written by stevebuchanan

March 2, 2012 at 12:23 pm

Photographic Term of the Week: Additive Color

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Additive color is the process of creating colors by combining light. IE, white light (neutral) would be created by combining equal amounts of red, green and blue light. Conversely, subtractive color is the process of creating colors by filtering reflected light. IE, black (neutral) would be created by filtering equal amounts of cyan, magenta and yellow. Additive color is used in transmissive displays (televisions, monitors, backlit transparencies) subtractive color is used in reflective displays (prints)

Note regarding subtractive color in commercial printing: Ideally the combination of C,M,Y inks would produce a perfect black, but in practice they do not. Therefore the addition of a fourth black ink (referred to as K) is used.

Written by stevebuchanan

February 17, 2012 at 9:41 am

Photographic Term of the Week: Barn Doors

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Barn Doors are light modifiers added to an artificial light. Usually consisting of two or four independently hinged cards or flags used to block light from a particular portion of a scene.

Written by stevebuchanan

February 10, 2012 at 9:38 am

Photographic Term of the Week: Bokeh

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Bokeh refers to the portion of an image that is rendered out of focus by the lens, or more specifically, the way a lens renders those out of focus portions. Various factors play into a particular lens’ bokeh affect and it’s quality. Bokeh is most visible in images that have a shallow depth of field, as those images have large portions of the image out of focus. Whether or not a lens is said to have “good” or “bad” bokeh is a function of its particular design, specifically aperture blade shape and optical characteristics.

Portion of an image showing bokeh

Written by stevebuchanan

February 3, 2012 at 10:34 am

Photographic Term of the Week: Color Temperature

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Color Temperature is the description of the color of a light source. Expressed in degrees Kelvin, it’s based on an ideal radiator of light at a particular temperature. Daylight is usually thought of as 5500˚K, incandescent usually 3200˚ or 3400˚ Perceptually, our brains don’t see this difference in color easily, but photographic sensors and films do. Manual or automatic color balance is fairly easily achieved with digital still and video cameras, but situations with differing light sources and therefore differing color temperatures can present challenges.

Written by stevebuchanan

January 20, 2012 at 10:46 am

Photographic Term of the Week: Bellows Factor

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Bellows factor is the degree which exposure is lessened due to the lens being focused beyond it’s focal length. Practically speaking – its the degree which we need to increase our exposure when we focus close. Bellows factors of 4 (2 stops) are not uncommon when shooting close work.

The focus mechanisms in our lenses effectively move the lens farther from the image plane as we focus closer to the subject. As we focus closer and the lens moves farther away from the plane, light falloff from the lens to the plane becomes apparent. This is rarely an issue in everyday photography, but in closeup work it’s very apparent. When working with available light and an in camera light meter, this effect is compensated for by the meter. But when using studio lighting the bellows factor must be manually accounted for.

Written by stevebuchanan

January 13, 2012 at 10:27 am

Photographic Term of the Week: Chromatic Aberration

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This week we begin a new series of defining photographic terms. This week…

Chromatic Aberration – (aka Achromatism) is a shortcoming of lenses where different colors of light are focused onto different planes. IE Blue wavelengths focusing nearer than red. Since all colors we see are made up of combinations of differing wavelengths of light chromatic aberration will cause a loss of sharpness in the color transitions occur. Generally speaking, higher end lenses reduce CA to the point where it’s not detectable with current camera systems.

Image by Stan Zurek

Other lens shortcomings (aberrations) include spherical aberrations, distortion and curvature of field.

Written by stevebuchanan

January 5, 2012 at 10:25 am