US4009928A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Three element varifocal lens systems
Assignee: Individual
•
Filing: 1975-06-27
•
Granted: 1977-03-01
•
Expires: 1995-06-27
Abstract
Abstract A three element varifocal lens system in which the front and back lens elements are stationary and the inner lens is shiftable from the telephoto to the wide angle position. The front lens is negative while the inner and back lenses are positive. The lens system has particular utility for infrared imaging systems.
Inventors
- 👤 Frank G. Back
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 17:11
CPC Classifications
G; G02; G02B; G02B13/00; G02B13/14; G02B15/00; G02B15/14; G02B15/143; G02B15/1435; G02B15/143507
Claims Analysis
Total Claims: 2
Claim 1
Independent Claim
155 words
A long back focal length varifocal lens system comprising three air spaced lens elements disposed along the optical axis of the system formed of a material having a high infrared wave length transmission comprising in the order of the entrant light beam, a stationary negative front lens, a longitudinally movable positive inner lens element and a stationary positive back lens element in which the lens system has the following optical characteristics: ______________________________________
Thickness (t)
Radius R Spacing (d) in mm
Lens No.
in mm (Wide Angle)
(Telephoto)
______________________________________
R.sub.1 = 1504.24
14 t.sub.1 = 5 t.sub.1 = 5
R.sub.2 = -476.17
d.sub.2 = 102.0
d.sub.2 = 2.35
R.sub.3 = 476.17
15 t.sub.3 = 7 t.sub.3 = 7
R.sub.4 = 3159.56
d.sub.4 = 5 d.sub.4 = 104.65
R.sub.5 = 63.13
16 t.sub.5 = 5 t.sub.5 = 5
R.sub.6 = -75.72
EFL = 48.17 EFL = 97.725
BFL = 65.92 BFL = 65.92
______________________________________
Material-Germanium-Refractive Index 4.003
Claim 2
Dependent Claim
155 words
A long back focal length varifocal lens system comprising three air spaced lens elements disposed along the optical axis of the system formed of a material having a high infrared wave length transmission comprising in the order of the entrant light beam, a stationary negative front lens, a longitudinally movable positive inner lens element and a stationary positive back lens element in which the lens system has the following optical characteristics: ______________________________________
Thickness (t)
Radius R Spacing (d) in mm
Lens No.
in mm (Wide Angle)
(Telephoto)
______________________________________
R.sub.1 = 1504.24
14 t.sub.1 = 5 t.sub.1 = 5
R.sub.2 = -476.17
d.sub.2 = 102.0
d.sub.2 = 2.35
R.sub.3 = 476.17
15 t.sub.3 = 7 t.sub.3 = 7
R.sub.4 = 3159.56
d.sub.4 = 5 d.sub.4 = 104.65
R.sub.5 = 63.13
16 t.sub.5 = 5 t.sub.5 = 5
R.sub.6 = -75.72
EFL = 48.17 EFL = 97.725
BFL = 65.92 BFL = 65.92
______________________________________
Material-Germanium-Refractive Index 4.003
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1980-02-29 | 1980-08-30 | 1981-03-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1984-02-29 | 1984-08-30 | 1985-03-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1988-02-29 | 1988-08-30 | 1989-03-01 | $7700.00 | Window Closed / Lapsed |