Video Autofocus (VAF) video autofocus system

brief introduction

Combined with analog cameras and focus control components, the Video Autofocus system provides a convenient focus control solution, including standard and piezoelectric XYZ platform systems, linear platform systems, and independent focus controllers.

The Video Autofocus system uses the spatial information present in the analog video signal to determine the focus value. Then, the firmware algorithm maximizes this focus value by adjusting the focus position using a focus driver. The autofocus option requires standard NTSC/RS170, PAL/CCIR, or S-Video analog video signals from the camera. By using dual output cameras or beam splitters, automatic focusing can be achieved through digital cameras.

The Video Autofocus system has high sensitivity and stability, and adopts an automatic calibration program to automatically adapt to various lighting conditions, different samples, and objectives.

function

• Fast Focus - A typical precise focus operation takes about one second and can be configured for faster operation.
• Precise Focus - In the presence of an "optimal focus" plane, Autofocus will automatically focus like an operator finding the focal point.
• Objective protection - For safety reasons, once zeroed, autofocus will not move more than 0.2 mm.
• Focus value reading - The focus value is always displayed on the LCD reading, so you can easily verify if the operation is correct.
• Video Region Selection - You can select a rectangular portion of the video as the focal area. Highlight the selected area on the monitor output.
• Automatic calibration - performs a series of scans and selects various internal parameters to achieve optimal focus.
• Focusing algorithm - can achieve automatic focusing through buttons on the controller or commands from the host.

Working principle

The Video Autofocus (VAF) system uses electronic circuits to detect high spatial frequency information present in video signals from analog cameras and convert it into focus values for each frame - the better the focus, the larger the focus value. The conditions for achieving the optimal focus value may vary for different samples and objectives. To compensate, the system integrates an automatic calibration program that can automatically set various internal parameters to achieve good focus values. The system also allows users to highlight any sub area of the video field and focus on the samples within it.

When the controller receives an autofocus command, it will move from the starting position to the stopping position and continuously check the autofocus signal. The focusing signal undergoes a filtering process to eliminate unnecessary false focusing caused by noise and other interference. In "normal" mode, the controller obtains the filtered signal and observes the maximum value. When a new maximum value is detected, the controller will track the location of the maximum value.

When the scan is complete, the controller will return to the position with the highest value. There is also a 'Hill Detect' mode available. In this mode, the autofocus controller observes an increase in focus value and then begins to decrease, thereby detecting a slope. At this point, the autofocus controller stops scanning and returns to the highest focus value found on the hill. This is somewhat susceptible to erroneous focusing and should only be used for high contrast single-layer samples with sharp edges.