Fast IR Fisheye Lens with Hyper-Hemispherical Field of View

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  • PARALLEL PROCESSING t o o l s f o r t o d a y ' s o p t i k e r

    Patent Design

    Fast IR Fisheye Lens with Hyper-Hemispherical Field of View

    BY J. BRIAN CALDWELL Patent: Issued: Title:

    Example: Inventor: Assignee:

    U.S. 5,502,592 March 26, 1996 Wide-Aperture IR Lenses with Hyper-Hemispherical Fields of View #3 of 5 Thomas H. Jamieson Lockheed Missiles & Space Company, Inc.

    In the May issue of OPN, I stated that fisheye lenses are normally designed to cover a full-field angle of 180. However, in a few cases the coverage is extended beyond 180 to encompass a hyper-hemispherical field of view. Since 1969, Nikon has manufactured a 6 mm f2/8 fisheye for 35-mm SLR cameras that covers a total field of 220.1 This design is described in a patent by Shimizu.2 Visible light designs covering a total field of 270 have been described in the patent literature by Van Heel3 and Is-shiki,4 however, these designs have relatively small apertures of f/10 and f/5.6, respectively.

    This month's patent design, shown in Figure 1 and listed in

    Table 1, is a fisheye lens for long wavelength IR (8-12 m wavelength range) that covers a full field of 270 at an astonishingly large aperture of f/0.7. This combination of field coverage and aperture is unprecedented, but in spite of the extreme specifications, the design is quite simple, consisting of only four germanium elements. The design would provide an interesting challenge to a manufacturer because the concave surface of the negative meniscus front element is hyper-hemispherical!

    The optical performance is excellent, and is fairly uniform over the entire field of view, as shown in the transverse ray aberration plots of Figure 2. Although the patent gives

    the field of view as 270, I was able to trace rays out to about 290 while maintaining reasonable aberration correction.

    References 1. B. Moose Peterson, Nikon System

    Handbook, 4th Edition (Silver Pixel Press, Rochester, NY, 1996), p. 74.

    2. Y. Shimizu, "Wide Angle Fisheye Lens," U.S. Patent 3,737,214 issued June 5, 1973.

    3. A.C.S. Van Heel et al., "Wide-angle Objective Lens," U.S. Patent 2,947,219 issued Aug. 2, 1960.

    4. M. Isshiki et al., "Achromatic Super Wide-Angle Lens," U.S. Patent 3,524,697 issued Aug. 18, 1970.

    OPN Contributing Editor J. Brian Caldwell (caldwell@ ods-inc.com) is a consulting lens designer and president of Optical Data Solutions, Inc., which produces LensVIEWTM, a database of optical designs found in the patent literature.

    Figure 1. 2 7 0 FOV, f / 0 . 7 IR f isheye lens .

    Figure 2. T r a n s v e r s e ray aberrat ions at w a v e l e n g t h s of 8, 1 0 , and 12 m for semi-f ie ld ang les of O, 9 0 , and 1 3 5 .

    Table 1. Opt ica l prescr ipt ion for the object ive focal length: 3 .4 m m ; aperture: f / 0 . 7 ; full f ield angle: 2 7 0 ; spec t ra l range: 8 - 1 2 m .

    Optics & Photonics News/July 1999 47