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Low-dispersion glass and APO Lenses |
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Written by openD
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Monday, 13 November 2006 |
 Uncorrected lenses can act like prisms, splitting white light and dispersing its constituent colors, to create fringes of color at the edge of objects in a picture. This is because the speed of light in glass depends on its color the red, green and blue light rays are blend to different extents and brought to a different focus. Apochoromatic (APO) lenses use special low-dispersion glasses in sophisticated combinations to focus all the colors at precisely the same level.
The new multi-layer lens coating and lens design of some quality makes reduces flare and ghosting, and creates an optimum color balance through the entire zoom range. Canon L series, Sigma APO series are within this range.
Sigma uses one aspherical lens and three SLD (Special Low Dispersion) glass elements for excellent correction all types of aberration, making high-quality images a reality throughout the entire zoom range. I have to admit that I have read many times that some Sigma lenses have a better optical quality than canon’s L series of lenses.
 Some Sigma lenses are equipped with ELD (Extra Low Dispersion) glass elements. Two ELD glass elements in the front lens elements reduce chromatic aberration to a minimum and also ensure sharp, quality images of high contrast.
About Sigma
∑ SIGMA is the Greek letter equivalent to the English letter "S." In mathematics, it's a sign used to show the total sum. For photographers everywhere, Sigma is the total sum of the research, development, manufacturing and service of the world's leading line of lenses and cameras. Sigma ensures a high, consistent level of quality by processing its own high-performance Special Low Dispersion glass (SLD), metal and resins, surface treatments and other elements right there inside their factory itself. Sigma coordinates the development, production and sales of its technology worldwide through an impressive network of offices in Japan, the United States, Germany, France, United Kingdom, the Benelux countries, Hong Kong and Singapore.
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Last Updated ( Monday, 13 November 2006 )
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