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Photography Terms You Might Not Know… But Should

2013-10-16 20:50:53 GMT

Sometimes as a photographer you stumble across some terminology that you feel like you might know, but then again… maybe you don’t. Here are some uncommon photography terminologies that won’t hurt to know.

Aberration.
Failing in the ability of a lens to produce a true image. There are many forms of aberration and the lens designer can often correct some only by allowing others to remain. Generally, the more expensive the lens, the less its aberrations (More attention to optical quality). While no single lens is called a ‘perfect lens’. The “ideal” lens would reproduce a subject in a faithful, clearly defined image on film. Aberrations, which can be divided in so six basic faults, affect the ideal performance in an optical systems.

a) Spherical aberration. Basically, a beam of light passing through a lens parallel to the optical axis converges to form 3 focused image on the film. Spherical aberration is the term for an optical fault caused by the spherical form of a lens that produces different focus points along the axis to focus on a curved surface rather than a plane.

b) Curvature of field. this optical defect causes points on an object plane perpendicular to the lens axis to focus points along the axis for central and marginal rays.

c) Astigmatism. Rays of light from a single point of an object which is not on the axis of a lens fail to meet in a single focus thus causing the image of a point to be drawn out into two sharp lines, one radial to the optical axis and another perpendicular to this line, in two different planes near the curvature of field.

d) Coma. This optical defect causes the image of an off-axis point of light to appear as a comet-shaped blur of light. Coma, as well as curvature of a field and astigmatism, degenerate the image forming ability of the lens at the rims of the picture.

e) Distortion. Even if the first four aberrations were totally eliminated, images could result that still have a distorted appearance. For example, a rectangle may appear as a barrel or pin cushion-shaped object.

f) Chromatic aberration. This aberration is caused by light rays of different wavelengths coming to focus at different distances from the lens. Blue will focus at the shortest distance and red at the greatest distance. Since the natural rays of light are a mixture of colors, each aberration will give a different value corresponding to each color thus producing blurred images.

Barrel Distortion.
Straight lines are bowed in at the edges of the picture frame resembling the sides of a barrel; present in small amounts in some wide-angle or wide-angle-zoom lenses, but uncorrected in fish-eye lenses.

Bayer Pattern.
The “Bayer” pattern is digital photography terminology to describe how photosites are arranged on an image sensor. A Bayer pattern has 50% green photosites, 25% red photosites and 25% blue photosites.

There are twice as many green photosites than red or blue because human eyes are most sensitive to green light.


Bracketing.
Taking a series of photographs of the same subject at different exposures to insure “correct” exposure; useful when shooting in situations where a normal metering reading is difficult to obtain. Taking additional pictures of the subject through a range of exposures-both lighter and darker-when unsure of the correct exposure. Some top cameras have provision for automatic bracketing, while manually you can bracket by adjusting apertures or shutter speeds or both, manually influent the ASA setting or even adjust the flash output power etc..



Bokeh.
Bokeh is a photography term that refers to the way a lens blurs and image.

Generally it is considered good practice, especially with portrait photography, to have the main subject in focus and the background blurred.

Bokeh refers to how evenly and pleasingly the out of focus (blurred) area looks.

Densitometer.
An instrument used for measuring the optical density of an area in a negative or print.

Foveon Sensor.
A type of sensor where the color recording layers are stacked on top of each other. This means that every “pixel” can record the level of red, green, and blue light hitting it.

This differs from the Bayer sensor, where each pixel can record only one color of light.

Kelvin.
A scale used to measure the color temperature. 5000 k refer to normal daylight.

Lossy/Lossless files.
When a digital camera takes a photo, the image data is stored on a memory card as a computer file. If the data is stored fully, the file is called a lossless file. These files are quite large in size. The most common type of lossless file in use are TIFFs.

To cut down on large file sizes, the camera can throw away parts of the data that the human eye probably won’t notice anyway. These files are called lossy. The most common type of lossy file are JPEGs. Caution should taken when using JPEGs if image quality is important.

Lux.
A measurement of the light intensity. One lux in video means light level of a candle light.


Microprism.
Minute glass or plastic structure of multiple prisms set in a viewfinder screen to act as a focusing aid. Breaks up an out-of-focus subject into a shimmer but images a focused subject clearly. Will not work satisfactorily at lens apertures smaller than f5.6.

Purple Fringing.

In digital photography terminology, purple fringing is an undesirable purple “rim” that surrounds areas of high contrast in a digital image.

It’s very obvious when photographing people against a bright (but not deep blue) sky.

The reasons for purple fringing aren’t clear, although it is generally accepted that poor quality lenses and poor quality sensors make it worse.

Refractive Index.
A technical term used to describe the effect of a lens in causing light rays to bend; important aspect in lens design.

** Definitions are from A Glossary of Photographic Terms: www.mir.com.my **
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