Image Sensor Shifting for Vibration-Free High Frame Rate Focus Detection
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Solution Overview
Problem
High frame rates in focus detection systems lead to increased vibration frequency of image sensors, causing unpleasant sounds and vibrations, and limiting the effectiveness of vibration-type low-pass filters in achieving desired optical low-pass filter effects.
Innovation Solution
An image capturing apparatus with a shifting unit that moves the incident position of light flux on the image sensor by a predetermined distance equal to or less than the pixel distance during charge accumulation, using processors or circuitry to implement periodic drive control and achieve focus detection signals, thereby mimicking the effect of an optical low-pass filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the image sensor is reciprocated at higher speed to increase frame rate, then focus detection speed is improved, but unpleasant sound and vibration are generated
Solution Approach 1:
The patent applies dynamics by making the image sensor movable rather than fixed. The image sensor is reciprocated in the optical axis direction during charge accumulation to create a vibration-type low-pass filter effect. This dynamic movement allows the system to achieve high frame rates while the sensor's position is actively controlled to prevent harmful vibrations and sounds, resolving the contradiction between productivity and harmful factors.
2Productivity
If the vibration frequency of the image sensor is increased to match high frame rates, then focus detection speed is improved, but the desired low-pass filter effect cannot be obtained
Solution Approach 1:
The patent applies parameter changes by adjusting the reciprocating distance and direction of the image sensor based on the frame rate. At high frame rates, the sensor is reciprocated by a larger distance in the optical axis direction during charge accumulation. This parameter adjustment ensures that the vibration-type low-pass filter effect is maintained regardless of the frame rate, resolving the contradiction between productivity and reliability.
3Reliability
If an optical low-pass filter is arranged on the incident surface side of the image sensor, then spatial aliasing is reduced, but the resolution of the image sensor is degraded
Solution Approach 1:
The patent applies mechanics substitution by replacing the conventional optical low-pass filter with a vibration-type low-pass filter. Instead of using a physical optical filter that degrades resolution, the system uses mechanical vibration of the image sensor during charge accumulation to achieve the low-pass filter effect. This substitution maintains the full resolution capability of the image sensor while effectively reducing spatial aliasing, resolving the contradiction between reliability and measurement precision.
Data Source
AI summary
An image capturing apparatus comprises an image sensor in which a plurality of pixels are arranged, wherein the plurality of pixels output focus detection signals based on light flux that has passed through an imaging optical system, a shifting unit that shifts an incident position of the light flux on the image sensor; and a focus detection unit that performs focus detection using the focus detection signals. The shifting unit shifts the incident position by a predetermined distance which is equal to or less than a distance between the pixels of the image sensor corresponding to the focus detection signals during a charge accumulation period in the image sensor for acquiring the focus detection signals.