Variable Magnification Finder with Nested Lens Groups
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Solution Overview
Problem
Conventional methods for achieving variable magnification in reverse-Galilean finders result in large lens movement, leading to increased finder size, which is not suitable for the thickness requirements of modern digital cameras.
Innovation Solution
A variable magnification finder design that includes a positive lens group, a negative lens group with negative refractive power, and an eyepiece lens group, where the positive lens group is retracted and the negative lens group moves during magnification changes, with focal lengths optimized to satisfy specific conditional formulas to reduce thickness while maintaining excellent optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a lens group is moved in the direction of the optical axis to achieve variable magnification, then magnification switching is realized, but the movement amount becomes large causing the finder size to increase
Solution Approach 1:
The patent implements nesting by placing the positive lens group inside the negative lens group. During high magnification, the positive lens group is inserted into the optical path within the negative lens group structure. During low magnification, the positive lens group is retracted to the outside. This nested arrangement allows variable magnification while minimizing the overall finder size and thickness.
Solution Approach 2:
The patent employs dynamic reconfiguration of the lens groups. The positive lens group can move between two positions: inserted into the optical path for high magnification and retracted for low magnification. The negative lens group also moves dynamically toward the object side during magnification change. This dynamic adjustment enables variable magnification without requiring a large fixed structure.
2Length of stationary object
If the finder thickness is reduced to meet modern camera requirements, then the camera body can be made thinner, but the lens movement amount increases making variable magnification difficult to achieve
Solution Approach 1:
By nesting the positive lens group within the negative lens group structure, the patent achieves compact thickness while maintaining variable magnification capability. The nested arrangement allows both lens groups to operate within a reduced thickness envelope, solving the contradiction between thin finder design and variable magnification functionality.
Solution Approach 2:
The patent utilizes conditional formulas to precisely control the focal lengths of the lens groups (fP and fN). By optimizing these parameters according to the specified relationships, the system achieves proper magnification switching within a reduced thickness, balancing the conflicting requirements.
3Adaptability or versatility
If the positive lens group is inserted into the optical path to increase magnification, then high magnification is achieved, but the finder thickness increases
Solution Approach 1:
The positive lens group is nested within the negative lens group structure, allowing it to be inserted into the optical path without significantly increasing the overall thickness. The nested configuration enables the lens groups to occupy overlapping spatial regions, achieving high magnification while maintaining a compact thickness profile.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design allows for switchable magnification with reduced thickness, excellent optical performance, and improved aberration correction, meeting the thickness and performance needs of modern digital cameras.
Implementation Method 1
a positive lens group (1) having positive refractive power; a negative lens group (2) having negative refractive power
Data Source
AI summary
The magnification of the variable magnification finder is switchable, and the finder includes a positive lens group, a negative lens group, and an eyepiece lens group in this order from an object side in a high magnification state. The positive lens group is retracted from an optical path of the variable magnification finder to the outside of the optical path and the negative lens group moves toward the object side when magnification is changed from the high magnification state to a low magnification state. The following conditional formula is satisfied when the focal length of the negative lens group is fN:−15 mm<fN<−5 mm.