Finder Optical System with Beam Height Expansion
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Solution Overview
Problem
Conventional finder optical systems for electronic viewfinders have limited design flexibility, resulting in short eye relief, vignetting, and color aberrations due to small display device sizes and wide view angles, leading to inconvenient user experiences.
Innovation Solution
A finder optical system comprising a first lens group with a bioconcave and bioconvex lens configuration that increases light beam height and a second lens group with a plastic aspherical convex lens to correct aberrations, ensuring telecentricity at the display device side and satisfying specific conditional equations for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a small display device is used with a wide view angle, then the finder size is reduced, but the eye relief distance becomes very short and the pupil diameter becomes very small
Solution Approach 1:
The finder optical system is divided into two functional groups: a first lens group dedicated to beam height expansion and a second lens group dedicated to image formation. This segmentation allows the first group to specifically address the eye relief issue by expanding the beam height, while the second group maintains image quality, thus resolving the contradiction between compact size and adequate eye relief.
Solution Approach 2:
The first lens group introduces an intermediate dimension by expanding the light beam height vertically before the light reaches the second lens group. This dimensional expansion effectively increases the eye relief distance without increasing the overall finder size, as the beam height expansion occurs in the vertical dimension rather than extending the optical path length.
2Area of moving object
If the view angle is widened, then the field of view is improved, but vignetting increases and the finder becomes hard to see
Solution Approach 1:
The first lens group performs a preliminary action by expanding the light beam height before the light enters the second lens group. This preliminary beam expansion ensures that light rays from wide angles are already properly positioned and sized, preventing vignetting from occurring in subsequent optical stages while maintaining the wide view angle.
3Volume of moving object
If the display device size is reduced, then the finder is more compact, but the eye relief distance becomes shorter
Solution Approach 1:
Instead of increasing eye relief by extending the optical path length (one dimension), the first lens group expands the beam height in the vertical dimension. This allows compact finder design while achieving adequate eye relief through vertical beam expansion rather than horizontal path extension.
4Length of stationary object
If the light beam height is increased by the first lens group, then the eye relief is prolonged, but astigmatism aberration may deteriorate
Solution Approach 1:
The optical system is segmented into two specialized groups: the first lens group (bioconcave + bioconvex) optimized for beam height expansion with controlled aberrations, and the second lens group (aspherical convex + bioconvex + concave meniscus) optimized for aberration correction. This segmentation allows each group to perform its specific function while minimizing negative side effects like astigmatism.
Solution Approach 2:
The lens groups use composite lens configurations combining different lens types (bioconcave, bioconvex, aspherical convex, concave meniscus) with different refractive properties. This composite approach allows the system to achieve beam expansion while correcting astigmatism and other aberrations through the complementary optical properties of the different lens elements.
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
The solution provides a longer eye relief, wider view angle, and reduced astigmatism aberration, making the finder optical system easier to use and improving image quality with reduced color blur and turbidity.
Implementation Method 1
a first lens group to increase a light beam height of a light beam bundle incident from a display device side and to emit the light beam bundle to the eye point side
Implementation Method 2
a second lens group having an image formation action
Data Source
AI summary
A finder optical system includes, in the order from a display device side to an eye point side, a first lens group to increase a light beam height of a light beam bundle incident from a display device side and to emit the light beam bundle to the eye point side, and a second lens group having an image formation action.