US2981167A - Pneumatic exposure regulating device for photographic cameras - Google Patents

Description

April 25, 1961 F. BIEDERMANN 2,981,167 PNEUMATIC EXPOSURE REGULATING DEVICE FOR PHOTOGRAPHIC CAMERAS Filed Aug. 2, 1957 INVENTOR. Friedrich B/EDERNANN A6 BY M1625 A TTOR NE Y3 United States Patent PNEUMATIC EXPOSURE REGULATING DEVICE FOR PHOTOGRAPHIC CAMERAS Friedrich Biedermann, Unterhaching, near Munich, Germany, assignor to Agfa Aktiengesellschaft, Leverkusen- Bayerwerk, Germany, a corporation of Germany This invention relates to a pneumaticexposure regulating device for photographic cameras including a perforated valve plate and a movable flow-obstructing memher, and more particularly relates to such a device in which the movement of the flow-obstructing member is photoelectrically controlled to permit it to block the orifices or perforations in the valve plate to a degree which varies in accordance with the existing available illumination for photographic exposure.

There are existing devices of the aforementioned general type, but heretofore known types of flow-obstructing members formed as thin foils of mica, have not allowed precise exposure regulation and have prevented the exposure regulation devices from properly operating.

In accordance with this invention, a thin flat and flexible flow-obstructing member, for connection to the movable coil of a galvanometer, for example, is made of a synthetic plastic material, more specifically for example, a polyester such as polyethylene terephthalate.

Further in accordance with this invention, at least one surface of this synthetic is coated with a very thin layer of electrically conductive material, for example, a highly conductive metal. This avoids troublesome electrostatic charging phenomena.

The flow-obstructing member in accordance with this invention has the advantage of ease of fabrication in a uniform thickness throughout. Also, it is supple and elastic and maintains its shape with freedom from distortion or deformation over great ranges of variation of temperature and humidity. This type of member, therefore, reliably provides precise metering characteristics.

To simplify manufacturing problems, an indicator or pointer for the aforementioned flow-obstructing member for cooperation with a scale and for indicating and permitting control of the functional position of the member at any given moment can be made together in one piece with the flow-obstructing member.

Novel features and advantages of the present invention will become apparent to one skilled in the art from a reading of the following description in conjunction with the accompanying drawings wherein similar reference characters refer to similar parts and in which:

Fig. l is a cross-sectional view in elevation of an embodiment of this invention, and

Fig. 2 is a cross-sectional view taken through Fig. 1 along the line IIII and looking in the direction of the arrows.

In Figs. 1 and 2 is shown a portion 1 of the camera housing including a plate 2, for example, horizontally disposed a short distance below the top of housing cover 3. A structural member 4 is mounted upon plate 2 for supporting cylinder 5 of a pneumatic shutter retarding device which automatically adjusts the exposure time provided by the shutter. This pneumatic retarding device is, for example, generally similar to the devices disclosed in Belgian Patent 516,387 granted on January 15, 1953, but this present device includes features not therein disclosed and as described in detail in the following.

r 2,981,167 Patented Apr. 25, 1961 This present pneumatic shutter retarding device includes a valve plate or disc 6 and a flexible diaphragm 8 which is secured between the wall of cylinder 5 and the bottom of a mounting ring 7 within which cylinder 5 is inserted. A rod 9 is connected substantially with the center of diaphragm 8 by means of opposed flanges. The other side of rod 9 is connected with a movable element (not shown) of the shutter (not shown). This movable element is characterized in that the exposure time provided by the shutter is a function of the speed of movement of the movable element. This movable element is, for example, the main drive member of the shutter.

A flow-obstructing element 10 is connected to the mov ing element (not shown) of a galvanometer 12 by means of an arm 11. Flow-obstructing element 10 is, for example, approximately elliptical in overall shape, and it is, for example, constructed of a synthetic or plastic material whose upper and lower surfaces are coated, for example, with a conductive metal to prevent electrostatic charging. More particularly element 10 is made of a thin sheet of a polyester resin, such as polyethylene terephthalate. A commercially available form of this resin is, for example, Mylar, which is a product of the du Pont Company of Wilmington, Delaware.

At least one of the flat surfaces of plastic member 10 is coated by a layer 19 of a conductive metal, for example, silver or copper as shown in Fig. 1 on both the upper and lower surfaces. This effectively prevents member '10 from becoming electrostatically charged during the course of its movement.

The moving element of the galvanometer '12 is, for example, a rotating coil which is electrically connected with a photoelectric cell (also not shown) of the photoelectric exposure regulating device. Flowobstructing member 10 is, therefore, moved with support arm 11 which is rotated by shaft 13 connected to the rotating galvanometer coil in accordance with the current developed by the photoelectric cell as it measures the ambient illumination to cover a greater or smaller amount of the perforations or orifices 14 incorporated in valve plate 6. These orifices or perforations are preferably of varying size.

The resilient nature of member 10 permits it to be pressed into contact with plate 6 to insure full coverage or obstruction of orifices 14. This can be accomplished I by a separate pressure member (not shown).

It has been found that the pneumatic exposure regulating device operates most precisely when the flow-obstructing member 10 has a thickness between 0.04 mm. and 0.07 mm.

In Fig. 1, diaphragm 8 and rod 9 are shown in the position that they assume when the shutter is cocked or tensioned. As the shutter is operated, diaphragm 8 and rod 9 move downward in response to movement of the main drive member of the shutter (not shown). This draws a flow of air through orifices 14, which flow is greater or smaller in accordance with the position of flow-obstiucting member 10 relative to valve plate 6 and its orifices 14. The retarding effect of diaphragm 8 on the movable element of the shutter to which it is connected is correspondingly smaller or greater to accordingly regulate the automatically controlled exposure time of the shutter. This exposure time is indicated on scale 46 by a pointer or extension 15 incorporated as part of flow-obstructing member 10. The position of extension 15 relative to the indicia on scale 16 is visible through a window 17. These indicia are constructed and arranged to indicate predetermined exposure times provided by corresponding positions of pointer 15 on flow-obstructing member 10.

A profile ring 18 is constructed and arranged to provide a curved space under valve plate 6 which maintains the volume of air between diaphragm 8 and valve plate 6 as small as possible when the shutter is in a tensioned condition and before it initiates a downward movement of diaphragm 8. Diaphragm S is therefore capable of being tightly maintained in contact with the adjacent surface of profile ring 18 when the shutter is in a tensioned condition as shown in Fig. 1.

What is claimed is:

1. A pneumatic exposure regulating device for photographic cameras comprising a flow-obstructing member, a pneumatic shutter retarding mechanism incorporating a perforated valve disc traversed by said flow-obstructing member, said flow-obstructing member comprising a relatively thin, highly flexible, flat sheet of a synthetic plastic material and at least one of the flat surfaces of said flow-obstructing member being coated with a layer of electrically conductive material.

2. A device as set forth in claim 1 wherein said flowing obstructing member is made of a sheet of a polyester plastic material.

3. A device as set forth in claim 1 wherein said flowobstmcting member is made of a sheet of polyethylene terephthalate.

4. A device as set forth in claim 1 wherein said flowobstructing member has a thickness between 0.04 mm. and 0.07 mm.

5. A device as set forth in claim 1 wherein said flowobstructing member incorporates an extension shaped in the form of a pointer, and said pneumatic exposure regulating device includes a scale having indicia which is traversed by said pointer.

References Cited in the file of this patent UNITED STATES PATENTS 2,800,844 Durst et al. July 30, 1957 FOREIGN PATENTS 489,348 Italy Jan/19, i954

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