Optical: systems and elements – Lens – With reflecting element
Patent
1993-03-26
1997-07-29
Nguyen, Thong
Optical: systems and elements
Lens
With reflecting element
359364, 359366, 359407, 359728, 359729, G02B 1700, G02B 2100, G02B 2300
Patent
active
056526792
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to optical systems for viewing devices such as binoculars and telescopes.
BACKGROUND OF THE INVENTION
Optical systems used in binoculars have optical paths folded by means of reflective prisms and are arranged to give erect images. The substitution of prisms by mirrors has been analysed in a paper "Camera viewfinder using tilted concave mirror erecting elements" by Donald DeJager in the SPIE Vol 237 at page 292 of 1980 but the arrangement was found unsatisfactory due to excessive amounts of astigmatism, variation of focus across the field, distortion and coma. Arrangements using erecting mirrors are also described in U.S. Pat. Nos. 4,598,981, 4,804,258, 4,758,077, 4,221,459 and 3,897,133. The first two do not incorporate any lenses and solely use mirrors which do not have an erecting function. The last three have circular fields and apertures with the last one having an annular aperture and it is known that annular apertures give poor visual images.
SUMMARY OF THE INVENTION
The present invention in one of its aspects aims at providing an approach whereby an optical system can use mirrors while giving acceptable performance with compact shape.
One aspect of the present invention provides an optical system for telescopes and binoculars having an optical path folded by erecting mirrors and comprising at least one lens characterized in that the system has an inherent aperture and field greater in a direction transverse to a direction in which the path is folded.
Normally the optical systems would have an objective lens unit and an eyepiece lens means with an additional aspect of the present invention providing an optical system for telescopes and binoculars comprising an objective lens unit and an eyepiece lens unit with an optical path there-between folded by erecting mirrors characterized in that the system has an aperture and field greater in a direction transverse to a direction in which the path is folded.
In use the greater field and aperture will be horizontal and the smaller field vertical. This will be acceptable for most uses such as scanning the horizon and permits a very advantageous binocular design to be designed with the optical paths folded tightly on themselves possibly in the shape of a Z or with the optical path folded so as to cross itself.
In the optical system the smaller field and aperture may be offset so that the optical system may otherwise be centered about a single axis as is the case in most optical systems where all the surfaces have their centers of curvature lying on a single axis.
The invention is not limited to the mirrors, objective lens unit and eyepiece lens means having spherical surfaces, but these can also be aspheric such as parabolic or toroidal. In this event such surfaces do not have a single point center of curvature and when used with off-axis apertures will tend to have centers of curvature blurred over a volume in space centered about two locations and with the volume increasing with increased aperture. The Gauss center of curvature or the center of curvature of the best-fit sphere can be taken as a representative value and will herein be termed the center of curvature. This center of curvature will also be used to define a mean radius of curvature.
It is convenient to define the positions of some of the centers of curvature in relation to a viewing axis which is the line joining the center of the viewed object to the center of the user's eye through the system when the system is being used.
It has been said that the folded path can be in the nature of a Z. The angles contained in the Z are preferably no greater than 30.degree. and this can be achieved by offsetting the used areas of the objective lens unit, mirrors and eyepiece lens means from the viewing axis possibly assisted by having the centers of curvature of the mirrors at distances not more than 20% but preferably less than 10% of their radii of curvature from the viewing axis and the centers of curvature of the objective lens unit and eyepiece
REFERENCES:
patent: 3897133 (1975-07-01), Warner et al.
patent: 3985421 (1976-10-01), Beecher
patent: 4221459 (1980-09-01), Fisher
patent: 4488790 (1984-12-01), Beecher
patent: 4497540 (1985-02-01), Breckinridge et al.
patent: 4598981 (1986-07-01), Hallam et al.
patent: 4758077 (1988-07-01), Beecher
patent: 4779969 (1988-10-01), Sato et al.
patent: 4804258 (1989-02-01), Kebo
patent: 4877318 (1989-10-01), Miles et al.
patent: 4940324 (1990-07-01), Nichols
SPIE, vol. 237, 1980 International Lens Design Conference Proceedings; D. de Jager: "Camera Viewfinder Using Tilted Concave Mirror Erecting Elements", pp. 292-298, See the Whole Article (cited in the Application).
Nguyen Thong
Optics and Vision Limited
Reynolds Locke
LandOfFree
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