Lens Apparatus Automatic Focus Control via Beam Splitter
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Solution Overview
Problem
Existing automatic focus systems in image-pickup apparatuses face precision issues when stopped down below a certain threshold, leading to vignetted pupils and inaccurate phase difference detection, particularly in moving picture shooting, which affects focus precision and can result in malfunctions.
Innovation Solution
A lens apparatus with a focus lens unit, zoom lens unit, aperture-stop device, splitting optical unit, focus-condition detection unit, and a controller that adjusts the focus lens movement based on the F-number, switching to manual operation when the F-number exceeds a predetermined value to prevent vignetting and ensure accurate focus detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a dividing optical unit is disposed on an image side of the aperture stop to perform phase-difference detection, then automatic focus control can be implemented, but when stopped down below a threshold value the pupil becomes vignetted causing inaccurate phase difference detection and focus precision deterioration
Solution Approach 1:
A beam splitter is introduced as an intermediary component to divide the light beam before it reaches the aperture stop. This allows the detection optical system to receive sufficient light for accurate phase difference detection even when the aperture stop is stopped down, preventing vignetting from affecting measurement precision while maintaining automatic focus control functionality
Solution Approach 2:
The optical path is segmented into a main imaging path and a detection path using the beam splitter. The detection path receives a portion of the light beam separately from the main imaging path, allowing independent optimization of light quantity for detection purposes without affecting the aperture stop settings for imaging, thus resolving the contradiction between automation and measurement precision
2Illumination intensity
If the aperture stop is stopped down to a small value to adjust light quantity, then light quantity is reduced for proper exposure, but the pupil becomes completely vignetted preventing phase difference detection and automatic focus control
Solution Approach 1:
The beam splitter acts as an intermediary that provides a dedicated detection path with sufficient light quantity independent of the aperture stop setting. This allows the aperture stop to be stopped down for proper exposure control while the detection path maintains adequate illumination for continuous automatic focus control
Solution Approach 2:
The system separates the light quantity control function (aperture stop) from the focus detection function (detection optical system via beam splitter). By creating an additional optical dimension for detection, the system can independently optimize light quantity for imaging without compromising automatic focus control capability
3Measurement precision
If a dividing optical unit is provided on an object side of the aperture stop to avoid vignetting, then phase difference detection accuracy is maintained, but the size of the entire optical system increases
Solution Approach 1:
Instead of placing the beam splitter on the object side before the aperture stop, the invention inverts the approach by placing it on the image side after the aperture stop. This reversal allows the detection path to receive light that has already passed through the aperture stop, ensuring accurate phase difference detection while avoiding the need for a larger optical system configuration
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
Enables precise automatic focus control and switching to manual focus when necessary, maintaining focus precision while preventing vignetting, and reducing the size and weight of the optical system.
Implementation Method 1
a splitting optical unit disposed between the aperture-stop device and the image-pickup element
Implementation Method 2
a focus-condition detection unit for detecting a focus condition based on light from the splitting optical unit
Data Source
AI summary
Provided is a lens apparatus mounted to a camera including an image-pickup element, including: a focus lens means movable in an optical axis direction for focusing; a zoom lens unit; a zoom detector for detecting a zoom value of the zoom lens unit; an aperture-stop device; a stop-value detector; a splitting optical unit; a focus-condition detection unit; an actuator; a controller for controlling the actuator based on an output from the focus-condition detection unit; and a manual operation member, wherein the controller obtains an F-number of the lens apparatus based on outputs from the zoom detector and stop-value detector and when the F-number exceeds a predetermined value, the controller causes the actuator to stop the focus lens unit and switches to a condition in which the focus lens unit is driven by the manual operation member.