Focus Adjustment Device Early Scan Stop Mechanism
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Solution Overview
Problem
Existing autofocus systems in image pickup apparatuses face challenges in accurately and efficiently determining the in-focus position, especially when dealing with mixed remote and near objects, as they often require multiple peaks detection and may not stop the scan operation at the optimal position, leading to increased autofocus time and lens driving.
Innovation Solution
A focus adjustment device and method that utilize a phase difference detection system and contrast detection system to repeatedly scan the focus lens, detect extreme values of contrast, and determine a stop position based on defocus amount, allowing the focus lens to be driven to the optimal in-focus position by calculating a minimum-scan position as a precedent to the phase difference in-focus position, thereby stopping the scan operation when a peak is detected before reaching this position and ensuring the contrast decreases after reaching it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple peaks detection is performed to ensure accurate focus on nearer objects, then focusing reliability is improved, but autofocus time increases
Solution Approach 1:
The patent calculates a determination start position in advance based on the defocus amount detected by the phase difference detection system, before the scan operation begins. This preliminary calculation allows the contrast detection system to stop scanning early when it reaches this predetermined position, avoiding unnecessary scanning beyond the point where accurate focus can be determined. The in-focus position calculation section computes this start position using the relationship between defocus amount and lens position, enabling the system to prepare stopping criteria beforehand.
2Reliability
If scan operation continues past the determination start position to detect all peaks, then focusing reliability is improved, but lens driving distance increases
Solution Approach 1:
The patent implements a feedback mechanism where the contrast detection system continuously monitors the contrast value during scan operation and compares it against the determination start position. When the scan position reaches the predetermined start position (calculated from defocus amount), the system receives feedback about the current contrast value and automatically stops scanning. This feedback loop prevents excessive lens driving by halting the scan at the optimal point where focus accuracy can be achieved without requiring the lens to travel the full range to detect all possible peaks.
3Speed
If phase difference detection is used to quickly estimate in-focus position, then autofocus speed is improved, but measurement precision for mixed objects deteriorates
Solution Approach 1:
The patent merges two different detection systems: the phase difference detection system and the contrast detection system. The phase difference detection system provides a quick initial estimate of the in-focus position and defocus amount, which is used to calculate a determination start position. The contrast detection system then performs scan operation with early stopping at this predetermined position. By combining the speed advantage of phase difference detection with the precision advantage of contrast detection, the system achieves both fast autofocus and accurate focus detection for mixed remote and near objects.
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 enables precise and efficient autofocus by minimizing lens driving and ensuring accurate focus on nearer objects, even in conditions with multiple peaks, by stopping the scan operation at the appropriate point and driving the focus lens to the detected peak position, thus reducing autofocus time and improving focusing reliability.
Implementation Method 1
a phase difference AF system is known in which focusing is performed by the pupil division type imaging plane phase difference detection system on the basis of a signal output from a focus detecting pixel row formed in, for example, an image pickup device
Implementation Method 2
A contrast AF system is also widely used in which focusing based on a contrast detection system is performed based on output signals from pixels for image pickup provided in an image pickup device
Data Source
AI summary
An extreme value detection section performs a scan operation to detect and store an extreme value of a contrast and a direction of change in the contrast while performing scan driving of a focus lens, based on a direction indicated by a defocus amount. A determination start position calculation section calculates a determination start position corresponding to a position of the focus lens where a determination whether the scan operation is stopped is started, as a position precedent to an in-focus position based on the defocus amount. A control section stops the scan operation if a maximum value is detected during the scan operation before the focus lens reaches the determination start position and it is determined that the contrast decreases as a latest change during the scan operation after the focus lens reaches the determination start position.