Photography – Having variable focal length of camera objective
Reexamination Certificate
2000-11-28
2002-06-18
Perkey, W. B. (Department: 2851)
Photography
Having variable focal length of camera objective
C396S074000, C396S088000, C396S147000, C396S150000, C396S505000, C359S448000, C356S003000
Reexamination Certificate
active
06408136
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The camera obscura (referred to hereinafter simply as “CO”) has been known for many hundreds of years. As its names implies, it was originally a dark (“obscure”) room (“camera”) with a small round hole in one of its walls, through which the outside view was formed as an upside down (inverted) image on an internal wall or screen opposite to the hole. Portable COs have also been known for at least three hundred years. The use of a lens inserted into the hole, which changes the CO into a photo-camera, appears to date back to the Renaissance. Portable cameras incorporating both lenses and a telescopic mechanism were known already in the 17
th
century. Such “telescopic” cameras had a box-within-a-box or tube-within-a-tube structure. The external box or tube had an external planar wall with a small hole fitted with a lens, and the internal box or tube had an internal planar wall parallel to the holed external wall, and covered by a semitransparent screen, sheet of paper, or similar material. The purpose of the telescopic structure was to bring the image formed by the lens on the semitransparent screen into focus.
The historical portable CO, in addition to being chiefly an amusement device, has been widely applied as a drawing aid. The teaching of various optical principles that form the basis of the CO effect is however invariably done with very simple implements. For example, in photography courses, students typically use improvised COs made of small boxes into which they drill a small hole. Prior art embodiments of a CO cannot illustrate the change in size of an image, which results from a change in the distance between the CO screen and a lens-less hole, the size change referred to herein as a “zoom” action of the CO. Known prior art embodiments also invariably use a fixed size hole, which determines the amount (intensity) of light entering the camera, and consequently the sharpness of the image. It is well known that a smaller hole reduces the light intensity but increases the sharpness (similar to the diaphragm action in a photography camera), however this effect is normally demonstrated by using different holes with different sizes in separate COs, in what we define as a “discontinuous” action, in contrast with the continuous diaphragm action of the present invention.
There is thus a widely recognized need for, and it would be highly advantageous to have, a portable camera obscura capable of demonstrating a zoom action and a continuous diaphragm action, as well as other principles of photography, all in one unit. Such a device will be referred to hereafter as a “zoom camera obscura” or simply a “zoom CO”.
SUMMARY OF THE INVENTION
According to the present invention there is provided a portable zoom camera obscura, comprising: a) a telescopic structure including an inner tube and an outer tube, each of the tubes having an inner and an outer end, the outer end of the outer tube constituting an imaging end, the outer end of the inner tube constituting a viewing end, the tubes positioned concentrically and slidingly movable relative to each other; b) a cover attached to the imaging end, the cover having a centered imaging hole; c) a screen covering the inner end of the inner tube; and d) a cover attached to the viewing end, the cover having a viewing hole.
According to one feature in the preferred embodiments of the zoom camera obscura of the present invention, there is provided a diaphragm disc pivotally mounted at its center to an off-center point on the cover of the imaging end.
According to another feature in the preferred embodiments of the zoom camera obscura of the present invention, the diaphragm disk includes at least one diaphragm aperture that can be positioned to provide a series of continuously changing overlap positions with the imaging hole.
According to yet another feature in the preferred embodiments of the zoom camera obscura of the present invention, there is provided a diaphragm ruler slidingly mounted on the cover of the imaging end.
According to yet another feature in the preferred embodiments of the zoom camera obscura of the present invention, the diaphragm ruler includes at least one diaphragm aperture that can be positioned to provide a series of continuously changing overlap positions with the imaging hole.
According to yet another feature in the preferred embodiments of the zoom obscura of the present invention, the diaphragm disk and the diaphragm ruler each include at least one lens.
The portable zoom camera obscura of the present invention is particularly useful as a teaching aid for teaching photography, graphic arts and science students the principles of the camera obscura and of photography, and as a general amusement device for young and old alike.
The present invention successfully addresses the shortcomings of the presently known configurations by providing a simple, portable device, which can illustrate not only the workings of the camera obscura and of a photographic camera together in one device, but can also show zoom and diaphragm effects without the presence of a lens.
REFERENCES:
patent: 822751 (1906-06-01), Mitchell
patent: 3185061 (1965-05-01), Westphalen
patent: 4560865 (1985-12-01), Bergström
patent: 5023641 (1991-06-01), Merrick
Pinhole Camera Activity, “The Pinhole Scope”, Dec.-1999, http://acept.la.asu.edu/PIN/act/pinhole/pinhole.shtml.
Friedman Mark M.
Perkey W. B.
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