1. Field of the Invention
The invention relates to an optical device, and more particularly to an optical device in which different lens frames are maintained to move coaxially.
2. Description of the Related Art
FIG. 1 is an exploded view of a conventional camera lens. FIG. 2 is a cross section of the conventional camera lens of FIG. 1. The camera lens 100 includes a first cam barrel 10, a first straight advance barrel 20, a first lens frame 30, a second cam barrel 40, a second straight advance barrel 50 and a second lens frame 60.
Three cam grooves 12 are formed on the first cam barrel 10, and three pins 14 are disposed on an outer periphery of the first cam barrel 10. Three straight grooves 22 are formed on the first straight advance barrel 20. The first lens frame 30 bears a first lens set (not shown) and has three pins 32 disposed on an outer periphery thereof. Teeth 42 are disposed on an outer periphery of the second cam barrel 40, so that the second cam barrel 40 can be rotated by a motor through a gear set (not shown) which engages the teeth 42. Cam grooves (not shown) and three straight grooves 44 are formed on an inner periphery of the second cam barrel 40. Three cam grooves 52 and three straight grooves 54 are formed on the second straight advance barrel 50. The second lens set 60 bears a second lens set (not shown) and has three pins 62 on an outer periphery thereof.
The second straight advance barrel 50 is disposed on a base (not shown) and within the second cam barrel 40 which is rotated by the motor through the gear set engaging the teeth 42. The second lens frame 60 is disposed within the second straight advance barrel 20, and the pins 62 of the second lens frame 60 extend through the straight grooves 54 of the second straight advance barrel 50 to engage the cam grooves (not shown) on the second cam barrel 40. The pins 14 of the first cam barrel 10 extend through the cam grooves 52 of the second straight advance barrel 50 to engage the straight grooves 44. The pins 32 of the first lens frame 30 extend through the straight grooves 22 of the first straight advance barrel 20 to engage the cam grooves 12 of the first cam barrel 10.
When the second cam barrel 40 is rotated by the motor and the gear set, the edges of the straight grooves 44 of the second cam barrel 40 push the pins 14 of the first cam barrel 10 to rotate the first cam barrel 10 so that the first lens frame 30, restrained by the straight grooves 22 of the straight advance barrel 20, is moved along a first axis L1. When the second cam barrel 40 rotates, the edges of the cam grooves (not shown) of the second cam barrel 40 push the pins 62 of the second lens frame 60. Thus, the second lens frame 60, constrained by the straight grooves 54 of the second straight advance barrel 50, is moved along a second axis L2.
In the described structure, the first lens frame 30 and the second lens frame 60 are required to move coaxially (i.e. the first axis L1 is coincident with the second axis L2, which can be accomplished by accurately manufacturing and fitting together the first lens frame 30, the first straight sleeve 20, the first cam barrel 10 and the second straight advance barrel 50. In practice, however, assembly of so many elements is liable to accumulated tolerance. As a possible result, the first axis L1 and the second axis L2 fail to coincide.