Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-03-21
2003-02-18
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S701000
Reexamination Certificate
active
06522481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cam structure of the zoom lens barrel assembly.
2. Description of the Related Art
In conventional zoom lens barrel assemblies, the mechanism that the frontmost lens-retaining barrel relies upon during extension and retreating is either a helicoid or a lead cam, each of which causes the frontmost barrel to advance in a linear fashion, or alternatively, a cam which causes the front most barrel to advance in a non-linear fashion. In the case of a cam being utilized, if the lens barrel is, for example, a two-lens group type, the profile of cam grooves is first determined for either one of the front lens group or the rear lens group. Subsequently, the profile of the cam grooves for the other lens group are determined based on the previously determined profile of the cam grooves.
If the cam grooves have a non-linear configuration for both of the lens groups, an optimum cam profile is designed on a development view of the cam ring. In this regard, it is difficult to estimate an ideal relationship between the rotation angle of the lens barrel and focal lengths in order to eliminate unnatural movement of the lens barrel and ensure smooth movement.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a method for determining the cam groove profile of the zoom lens barrel assembly which particularly facilitates otherwise difficult determination of the cam groove profile for wide-angle zoom lenses having a high zoom ratio.
For example, in an embodiment, a cam structure for a zoom lens barrel assembly, the zoom lens barrel assembly including a zoom lens system having a first lens group, the first lens group including a first sub-lens group and a second sub-lens group which move integrally during zooming, and a second lens group, wherein the first and the second lens groups move relative to each other along an optical axis upon zooming; and a sub-lens group switching mechanism for moving one of the first sub-lens group and the second sub-lens group away from the other of the first and second sub-lens groups in a short focal length photographing range, and toward the other of the sub-lens groups in a long focal length photographing range. The cam structure includes a zoom cam ring having a front lens group cam groove and a rear lens group cam groove for moving the first lens group and the second lens group toward and away from each other during zooming; wherein the front lens group cam groove and the rear lens group cam groove are determined according to the following equation:
C=B
+(
A−B
)*
K
(1);
wherein 0<K<1;
A designates a position of the other sub-lens group;
B designates a position of the second lens group; and
C designates a position of an imaginary point between the position A of the other sub-lens group and the position B of the second lens barrel.
The front lens group cam groove and the rear lens group cam groove can be determined so that when the position C of the imaginary point, corresponding to the minimum focal length position of the zoom lens system, and a point corresponding to the maximum focal length position of the zoom lens system are connected to each other, the position A and the position B, which each corresponding to a predetermined focal length, satisfy the above equation (1).
It is desirable for the coefficient K to be approximately 0.5.
The rear lens group cam groove can include a first portion corresponding to the short focal length photographing range and a second portion corresponding to the long focal length photographing range, the first and the second portions connected to each other via a discontinuous portion. The front lens group cam groove can include a non-linear portion which corresponds to the short focal length photographing range and provides a non-linear path, and a linear portion which corresponds to the long focal length photographing range and provides a linear path.
In an embodiment, the position of the imaginary point C moves in a straight line as the rotation angle of the zoom cam ring is varied so as to define an imaginary line CL, and wherein the position of the imaginary point C is extended to a position at the telephoto extremity, based on the position A at the telephoto extremity.
In an embodiment, the imaginary line CL is determined by passing through a plurality of the imaginary points C at the short focal length photographing range so as to form a straight line with respect to the rotation of the zoom lens barrel.
In an embodiment, an interpolation curve is obtained between the position A and the imaginary point C at the short focal length photographing range, and a tangent of the interpolation curve is taken at a telephoto extremity of the short focal length photographing range, wherein the position of the imaginary point C which corresponds to the position A at the telephoto extremity of the long focal length photographing range is obtained.
In an embodiment, the inclination of the imaginary line CL which connects the imaginary points C is determined from rotation angle of the zoom lens barrel from the wide-angle extremity to the telephoto extremity, and the displacement of the imaginary point C from the wide-angle extremity to the telephoto extremity; and wherein the correlation between each of stepped focal lengths and a rotation angle of the zoom cam ring is determined by the inclination of the imaginary line CL and the displacement of the imaginary point C with respect to wide-angle extremity.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2001-82095 (filed on Mar. 22, 2001) which is expressly incorporated herein by reference in its entirety.
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Ishizuka Kazunori
Nomura Hiroshi
Sasaki Takamitsu
Takashima Maiko
Greenblum & Bernstein P.L.C.
Mack Ricky
Pentax Corporation
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