Athermalized focal length extender for a zoom lens having a spli

Details Athermalized focal length extender for a zoom lens having a spli Athermalized focal length extender for a zoom lens having a spli

1998-11-24

2000-08-15

Epps, Georgia

Optical: systems and elements

Lens

Selective magnification by exchanging or adding a lens...

359688, 359820, 359676, G02B 1502, G02B 702

Patent

active

061045462

ABSTRACT:
An extender lens group removably incorporated in a zoom lens equipped with a temperature compensating feature for increasing the prim-lens focal length to achieve increased magnification is comprised of a front extender lens sub-group including four lens elements and a rear extender lens sub-group including two lens elements, the front extender lens sub-group including two positive bi-convex lens elements each of which has a strong curvature at the subject side surface followed by an overall positive doublet comprising a positive bi-convex lens element with a strong curvature at the subject side surface and a negative bi-concave lens element with a strong curvature at the image side surface and the rear extender lens sub-group including an overall positive doublet comprising a bi-concave lens element with a strong curvature at the image side surface and a positive meniscus lens element with a concave surface on the subject side. The extender lens group satisfying the following conditions: ##EQU1## where P1 is the temperature coefficient of refraction index of the negative lens element in the front extender lens sub-group and P2 is the temperature coefficient of refraction index of the positive lens element in the rear extender lens sub-group, the P1 and P2 being defined by dn/dt relative (.times.10.sup.-6 /.degree.C.) for a wave length of e-line.

REFERENCES:
patent: 2453218 (1948-11-01), Grey
patent: 4632520 (1986-12-01), Yamakawa
patent: 5745298 (1998-04-01), Yahagi

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