Photography – Single lens reflex camera – With mirror support or drive
Reexamination Certificate
2000-03-15
2001-12-04
Epps, Georgia (Department: 2873)
Photography
Single lens reflex camera
With mirror support or drive
C396S249000, C396S355000, C359S254000
Reexamination Certificate
active
06325554
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 an image reflecting mirror for the viewfinder in the camera.
BACKGROUND OF THE INVENTION
Viewfinder
When taking a picture it is necessary to know not only in what direction to aim the camera, but also how much of the subject will be included in the picture. For this reason, practically every camera available today has a viewfinder of some kind.
The viewfinder of a single-lens reflex (SLR) camera is relatively complex. Typically, an objective or front taking lens forms an image of the subject (by focusing rays of light reflected from the subject) on a ground glass viewing screen in the viewfinder via a mirror. The mirror is normally positioned at a 45° angle between the front taking lens and a rear film plane to reflect the light rays from the taking lens to the ground glass screen, instead of allowing the light rays to reach the film plane. The image formed on the ground glass screen is right-side-up, but is reversed left-to-right. A roof pentaprism is placed just above the ground glass screen in the viewfinder to provide eye-level viewing of the image and to reverse the image to orient it correctly, right-to-left. When you look through a rear eye lens in the viewfinder, the image you see is substantially the same as will be exposed on a film frame at the film plane. Since the distance from the front taking lens to the ground glass screen is the same as the distance from the taking lens to the film plane, the image exposed on the film frame will be sharp when the image has been similarly focused on the screen. During exposure, the mirror is pivoted upward to the ground glass screen from its 45° position to permit the light rays from the front taking lens to reach the film plane.
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 overly 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. Nos. 4,248,501 issued Feb. 3, 1981, 4,704,707 issued Nov. 3, 1987, 5,233,459 issued Aug. 3, 1993 and 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.09/526,332 discloses a camera with an electrostatic light valve (ELV) that functions as a diaphragm.
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 generally comprising a lens for forming an image of a subject by focusing rays of light, and a mirror for a viewfinder which is movable in the way of the light rays from the lens to reflect the light rays and is movable out of the way of the light rays to allow the lens to focus the light rays without the mirror reflecting them, is characterized in that:
the movable mirror is constructed to curl into a coil to move out of the way of the light rays to not reflect them and to uncurl from said coil to be in the way of the light rays to reflect them.
According to another aspect of the invention, a method in a camera of moving a mirror for a viewfinder in the way of rays of light from a lens to reflect the light rays and out of the way of the light rays to allow the lens to focus the light rays without the mirror reflecting them, is characterized by the steps of:
curling the mirror into a coil to move the mirror out of the way of the light rays to not reflect them; and
uncurling the mirror from the coil to move the mirror in the way of the light rays to reflect them.
Preferably, the invention is embodied in a camera having an objective lens for forming an image of a subject by focusing rays of light on a film plane, and a mirror for a viewfinder which is movable in the way of the light rays between the objective lens and the film plane to reflect the light rays to a viewing screen in the viewfinder and is movable out of the way of the light rays to allow the lens to focus the light rays on the film plane. The movable mirror includes a transparent flat stationary electrode between the objective lens and the film plane, and a coilable mirrored resilient electrode having one end fixed with respect to the stationary electrode and a free end. The coilable electrode is biased to curl into a coil on the stationary electrode, beginning at the free end, to move out of the way of the light rays, and is electrostatically actuatable to uncurl from the coil along the stationary electrode to be in the way of the light rays to reflect them to the viewing screen.
Thus, the invention preferably incorporates an electrostatic light valve(ELV) in a camera to function as the image reflecting mirror for the viewfinder in the camera.
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Eastman Kodak Company
Epps Georgia
Fields Roger A.
Tra Tuyen
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