| 摘要 |
A wide angle lens especially suitable for digital single lens reflex cameras is described. The lens offers the advantages of superior performance while using fewer lens elements thus reducing size and cost to manufacture. The lens consists of two lens groups separated by an aperture stop. The first lens group consists of a meniscus lens and the novel use of a bi-concave lens element. The first group may also include a cemented doublet with novel ratios of refractive index and Abbe numbers. Embodiments of the wide angle lens satisfy conditional equations of 6≦̸BFL/f≦̸7.5 and 10<&Sgr;d/f≦̸21, where BFL is the distance from the most image side lens element surface to the image plane with the lens focused at infinity, f is the effective focal length of the wide angle lens and &Sgr;d is the distance from the most object side lens element surface to the most image side lens element surface.
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