1995-05-11
1998-10-20
Blankenship, Howard B.
G03B 1704
Patent
active
058254617
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to bellows for optical equipment.
Bellows have been used in optical, particularly photographic, equipment for many years.
Typically such a bellows defines a light-tight tube between a lens and a film emulsion or other light-responsive recording medium. The bellows is not self-supporting, and is carried between a lens at one end and the camera body at the other, the lens being mounted on rails and moveable back and forth along the optical axis of the equipment.
A lens hood is a useful accessory intended to be fitted on the front of a camera lens or of optical accessories (filters etc) to screen the optical surfaces from incident sunlight or other unwanted light source. The lens hood however must not mask the field of view of the lens, and this causes difficulty with variable focal length (zoom) lenses.
A lens hood with a wide enough field of view not to mask the lens when set at its shortest focal length will be ineffective when the lens is zoomed to its telephoto mode with a narrow field of view. Conversely a lens hood suited to the telephoto mode will mask the lens when zoomed to wide-angle.
SUMMARY OF THE INVENTION
The present invention has an object the provision of a lens hood of adjustable axial length, and therefore field of view, but which avoids the need for a heavy and unwieldly supporting rail. The invention contemplates the use of a novel bellows construction which may be of use for other purposes in optical equipment. For example, it may advantageously be employed in large-format cameras in which support structure has hitherto been necessary (in addition to the lens guide rails mentioned above) to support the bellows and prevent it sagging.
The invention provides bellows for optical equipment comprising a tubular concertina structure of adjustable axial length, the folds of the concertina structure acting as hinges, said structure having portions of laminated construction, a first layer of said construction being of flexible light-inhibiting material and a further layer being of load-bearing material which stiffens the folds whereby upon axial adjustment the bellows retains its configuration without external support or restraint.
The load-bearing material may be plastically deformable at the folds to permit adjustment of the axial length of the bellows.
Preferably, the load-bearing material is substantially continuous across the folds of the concertina structure.
Included in the term "substantially continuous" are arrangements in which the load-bearing material is perforated at intervals along the line of a fold, the remaining material providing a plurality of connections between the load-bearing material in axially adjacent pleats of the bellows which connections are distributed along the length of the fold. Thus the connections may occupy at least 50% of the length of the fold, and preferably at least 75%.
The bellows may be of constant axial cross-section or may diverge, e.g. from one end to the other.
The layer of load bearing material may be sandwiched between two layers of light-inhibiting material.
The tubular structure may be polygonal in cross-section perpendicular to its longitudinal axis with an even number of sides, portions of the load bearing material being dispersed in side portions of the polygonal structure, said portions of load bearing material being separate from each other.
In a preferred form of the invention the portions of load bearing material do not extend to the corners of the polygonal tubular structure, the flexible material being folded at said corners to permit the adjustment of the axial length.
The folds in the flexible material may form bevelled corners on the polyhedral tubular structure, which preferably is four-sided.
The included angle of the concertina folds may change through twenty degrees or less when the bellows is moved from a fully extended to a fully retracted position. Preferably, the change in the included angle is about 10 degrees, or between 5 and 10 degrees.
The load bearing material may be
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patent: 1500391 (1924-06-01), Hutchings
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patent: 4205895 (1980-06-01), Yurdin et al.
patent: 4325769 (1982-04-01), Moyse et al.
patent: 4547053 (1985-10-01), Tobler
patent: 4662734 (1987-05-01), Nishi
Blankenship Howard B.
Miller Matthew
Panavision Europe Limited
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