 BetterPhoto Member |
APO and Aspherical Lenses I will be taking another trip out to Montana this summer and I need to replace my zooming telephoto lens. I would like to purchase a high quality one without unnecessarily spending a wad of money. I've read Sigma's descriptions of APO and Aspherical. Sigma manufactures both types with dispersion glass. Which one of the two would be of higher quality?
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Jon Close |
APO and Aspheric models in the Sigma line are of similar quality. The two types address different problems. As explained at Sigma's Web site, APO is more commonly used in telephoto zooms to correct for chromatic aberrations (different wavelengths of light focusing at different points). Aspheric elements are more commonly used in wide-angle zooms to correct for spheric aberrations (rays entering the outter portion of a sherical lens focus to a different point than rays through the center).
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