Focus Control Apparatus Using Multi-Area Phase Difference Detection
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Solution Overview
Problem
Existing focus control methods, such as on-imaging plane phase difference detection, struggle to maintain a stable in-focus state when the main subject moves or is switched during photography, often fixing focus on the background instead of the new subject due to limitations in AF frame settings and face detection methods.
Innovation Solution
A focus control apparatus and method that periodically acquires image signals from an image sensor to detect focus states using phase differences between signals from a primary and secondary area, adjusting focus control based on the detected states to ensure the main subject remains in focus, even when the secondary area is not within a predetermined range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a wider AF frame is set to maintain focus on moving subjects, then focus followability improves, but the system may incorrectly focus on background elements instead of the main subject
Solution Approach 1:
The imaging screen is divided into multiple focus detection areas with different priorities (first priority area, second priority area, etc.). The system segments the detection task by assigning different weights and roles to different regions, allowing precise control over which area's focus state determines the overall focus control, thereby preventing background from interfering with main subject focus.
Solution Approach 2:
Different areas of the imaging screen are assigned different qualities or weights for focus detection. The first priority area (where the main subject is located) is given higher weight than the second priority area (peripheral areas). This local differentiation ensures that the focus control system prioritizes the main subject over background elements, even when using a wide AF frame.
2Ease of operation
If the AF frame is set at the center for standard composition, then focus control is simple, but it cannot maintain focus when the subject moves to peripheral areas
Solution Approach 1:
The system dynamically adjusts the priority of different focus detection areas based on subject position and detection results. When a subject is detected in a peripheral area, that area's priority is increased, and the AF frame or priority areas are dynamically repositioned to track the subject, maintaining both simplicity and adaptability.
Solution Approach 2:
The system continuously monitors focus detection results from multiple areas and uses this feedback to adjust focus control. When the subject moves or is detected in a different area, the feedback mechanism triggers recalibration of priority areas and focus control parameters, enabling the system to adapt to moving subjects while maintaining operational simplicity.
3Adaptability or versatility
If multiple focus detection areas are used to cover wide range, then subject detection capability improves, but calculating defocus amount becomes complex
Solution Approach 1:
The system segments focus detection into priority levels, with the first priority area serving as the primary reference for defocus calculation. This segmentation simplifies the calculation by establishing a clear hierarchy: the first priority area's defocus amount is the primary control parameter, while other areas provide supplementary information only when needed, reducing overall computational complexity.
Solution Approach 2:
The system introduces a priority-based selection mechanism as an intermediary between multiple focus detection areas and the final focus control. This intermediary selectively chooses which area's defocus amount to use based on priority levels and subject detection results, simplifying the complex task of combining data from multiple areas into a single focus control parameter.
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 approach effectively maintains the in-focus state on the main subject during both still and moving image shooting, preventing the focus from locking onto the background by dynamically adjusting focus control based on the detected focus states from multiple areas.
Implementation Method 1
a defocus amount is calculated from a phase difference between a pair of image signals obtained by receiving light beam passing through mutually different exit pupil regions of an imaging optical system
Data Source
AI summary
In a focus control apparatus, an acquisition unit periodically acquires a pair of focus detection signals, a focus detection unit detects a focus state of a first area using a phase difference and, in a case where the focus state of the first area is not within a first range, detects a focus state using a phase difference in a second area arranged in a periphery of the first area, and a control unit controls to perform focus control. The focus control is performed based on the focus state of the second area if it is within a second range and, if a subject exists on a near side, focus control is performed based on the focus state of the first area regardless of the focus state of the second area being detected or not.