Photography – Camera detail – Diaphragm
Reexamination Certificate
2000-03-15
2002-09-03
Adams, Russell (Department: 2851)
Photography
Camera detail
Diaphragm
C296S203030, C296S203030
Reexamination Certificate
active
06443637
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of photography, and in particular to cameras. More specifically, the invention relates to a camera with an electrostatic light valve (ELV) that functions as a diaphragm.
BACKGROUND OF THE INVENTION
Diaphragm
The diameter of a given bundle of light rays passing through an objective lens in a camera determines the brightness of the image formed at the film plane. The maximum diameter of this bundle of light rays depends on the optical diameter of the lens. By placing opaque plates with holes of various sizes, or a set of opaque leaves to form an adjustable aperture, in the light path of the lens, it is possible to adjust the diameter of the bundle of light rays, and hence the intensity of illumination of the image formed at the film plane. The device with such a hole is commonly known as a diaphragm. A small hole formed by the diaphragm lets less light through the lens than a large one, so the size of the hole can be used to alter the exposure at the film plane.
In a lens which has only one optical element, the diaphragm may be placed in front or behind the optical element. The position affects the distortion of the image formed at the film plane: if in front, it tends to produce barrel distortion, and if behind, it tends to produce pin-cushion distortion. In a lens with several optical elements, the diaphragm is typically placed between two of the optical elements—e.g., a symmetrical lens has the diaphragm inserted midway between each of the identical elements (in the exact center of the lens).
The most common type of diaphragm is the variable opening or iris diaphragm. The hole in this type is formed by a circular series of thin opaque leaves. Movement of a control closes the leaves inward or opens them out to make the hole smaller or larger. Usually, the f-number of the resulting aperture is indicated on a scale alongside the control. The greater the number of leaves in the iris diaphragm, the more nearly the hole approaches a perfectly circular shape. However, a truly circular hole is by no means essential for every photography.
On modern automatic cameras, adjustment of the diaphragm to vary the size of the aperture is often controlled by an exposure meter which measures light intensity. The light measurement provided by the light meter is used to move the leaves of the diaphragm to form different size apertures. This takes place immediately before a shutter is opened to initiate the exposure. The speed of the shutter (which determines the duration of the exposure) also is derived from the measurement provided by the light meter.
Electrostatic Light Valve
An electrostatic light valve (ELV) consists of a transparent flat stationary electrode, a movable coil-biased resilient sheet electrode, and an insulating layer separating the two stationary and coilable electrodes. The coilable electrode has one end that is fixed with respect to the stationary electrode and a free end that is innermost within the coil when the coilable electrode is coiled. The coilable electrode is caused to unroll (uncurl) along the stationary electrode to overlay the stationary electrode when an electric potential (voltage) is applied between the two electrodes. As long as the electric potential is applied, the coilable electrode remains unrolled along the stationary electrode. Conversely, when the electric potential is discontinued the coilable electrode is reversed along the stationary electrode to re-coil (re-curl). The coilable electrode can thus act as an electrostatically actuated light valve or light shutter. This is disclosed in prior art U.S. Pat. No. 4,248,501 issued Feb. 3, 1981, U.S. Pat. No. 4,704,707 issued Nov. 3, 1987, U.S. Pat. No. 5,233,459 issued Aug. 3, 1993 and U.S. Pat. No. 5,784,189 issued Jul. 21, 1998. The prior art patents are incorporated in this application.
THE CROSS-REFERENCED APPLICATIONS
Cross-referenced application Ser. No. 09/526,190 discloses a camera with an electrostatic light valve (ELV) that functions as an image reflecting mirror for a viewfinder.
Cross-referenced application Ser. No. 09/526,709 discloses a camera with an electrostatic light valve (ELV) that functions as a variable format mask in a viewfinder.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a camera comprising an objective lens for forming an image of a subject by focusing rays of light at a film plane, and a diaphragm for forming a variable size aperture for the lens that changes the amount of light from the lens, is characterized in that:
the diaphragm has a series of coilable light valves constructed to curl into respective coils and to uncurl from the coils to change the size of the aperture.
According to another aspect of the invention, a method in a camera of adjusting a diaphragm to vary the size of an aperture for an objective lens, in order to change the amount of light that can pass through the objective lens, is characterized by the steps of:
curling a series of coilable light valves into respective coils to make the size of the aperture larger so that more light can pass through the objective lens; and
uncurling the coilable light valves from the coils to make the size of the aperture smaller so that less light can pass through the objective lens.
Preferably, the diaphragm for the objective lens includes a circular series of coilable resilient opaque electrodes that are biased to curl into respective coils radially outward to make the size of the aperture larger and are electrostatically actuatable to uncurl from the coils radially inward to make the size of the aperture smaller, a transparent flat stationary electrode that is positioned parallel to the coilable electrodes when the coilable electrodes are uncurled from the coils, a peripheral conductor that encircles the coilable electrodes and has respective conductive connections to each one of the coilable electrodes, and one conductive lead attached to the peripheral conductor and another conductive lead attached to the stationary electrode for together applying an electric potential between the coilable electrodes and the stationary electrode to electrostatically actuate the coilable electrodes to uncurl.
Thus, the invention preferably uses an electrostatic light valve(ELV) in a camera to function as a diaphragm for an objective lens,
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Adams Russell
Eastman Kodak Company
Fields Roger A.
Smith Arthur A
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