Selecting the ideal Precision autofocus (AF) sensor for your imaging application high-throughput microscopy and inspection systems depend on stable focus to protect image quality, yield, and throughput. WDI’s PFA autofocus (AF) sensors provide fast feedback for a Z-axis servo loop, helping the microscope stay in focus during motion and scanning. Two leading options are PFA-LN (line pattern) and PFA-DT (dot pattern). Both are designed for high-speed, accurate, repeatable focus tracking, but they provide different solutions for different application types. 

What both OEM laser autofocus sensors deliver

Both PFA-LN and PFA-DT autofocus (AF) sensor measure the distance between the objective and the sample surface independently of the imaging camera, enabling continuous autofocus without interrupting image capture. Using through-the-lens (TTL) principle of operation to measure the direction and distance to focus, the sensor projects a structured laser pattern through the objective and analyzes the returned pattern to determine the direction (up/down) and amount of focus correction. They provide fast, repeatable focus feedback to drive a Z-axis actuator (moving the objective or sample), so focus is maintained automatically during motion and scanning. The sensors also support PC integration via Gigabit Ethernet / RS485, with configurable outputs (including analog and step/direction) to match different control architectures. 

PFA‑DT: Dot-based tracking with high sampling rate and OA lens options

Driven by demand from the biomedical industry for fast and accurate autofocus solutions, WDI developed and refined its technology to create PFA-DT.  PFA-DT autofocus (AF) sensor uses a single-dot pattern and offers advancements in speed, accuracy, processing, and communication, at an affordable price.

• Continuous focus on multi-layer, including immersion objectives.
• Offset Adjuster (OA) lens versions are available to compensate for variances between the sensor focal plane and the camera imaging plane.
• High update rate and fast measurements result in high-speed tracking performance, Up to 8 KHz sample rate and improved processing power, coupled with Gigabit Ethernet communication create the fastest autofocus solution available today. 
• Featuring configurable output supporting both analog output and digital step and direction, making it a universal solution that can interface with Piezo actuators, Dover Motion’s DOF-5, WDI’s new integrated       Z stages, and other third-party Z-axis stages.
• Real-time diagnostic and performance reporting with insightful analytics and statistical metrics.

Best fit examples:

• Cost effective Autofocus solution for bare glass/silicon applications
• Systems prioritizing the highest sampling rate in a dot laser architecture
• Ideal for biomedical live cell, high content screening, genotyping and DNA sequencing applications

PFA‑LN: Fast integration, strong performance on patterned and multi-surface samples

PFA-LN autofocus (AF) sensor uses a line structured-light pattern and Advanced Multi-Segment Processing to improve autofocus performance on complex, patterned, and multi-layer samples such as semiconductor wafers and OLED displays. A new optical design, paired with increased processing power and memory, helps maintain stable tracking under challenging surface conditions. With Gigabit Ethernet connectivity and advanced surface recognition, PFA-LN autofocus (AF) sensor delivers reliable, consistent, high-speed focus for demanding applications. 

• Up to 3 kHz sample rate with enhanced processing for high-speed tracking performance.
• New 30° built-in optical design helps handle rectilinear patterns without external mechanical rotation.
• Configurable outputs (analog and digital step/direction) making it a universal solution than can interface with piezo actuators, Dover Motion’s DOF-5, WDI integrated Z stages, and other third-party Z-axis stages.

Best fit examples:

• Semiconductor / flat panel inspection where surfaces can be patterned and focus must stay stable during scanning.
• Platforms that benefit from a longer working standoff (up to 300 mm).
• Higher laser power for low reflectance application

How to choose the right autofocus solution

Choose PFA‑DT if: 

• You want a dot-pattern solution with the highest sampling rate (up to 8 kHz). 

• Your wavelength choice is within 660/785/850 nm and Class 1 / 1M laser classifications are preferred. 

• You need a cost-effective solution 

Choose PFA‑LN if: 

• You need a more advanced Autofocus solution  

• You want line‑pattern tracking with built‑in features for patterned, challenging and multi‑surface samples. 

• Your wavelength choice is within 450/ 660/785/850 nm and Class 3R classification is preferred 

Both autofocus sensors reflect WDI’s commitment to precision, modularity, and OEM integration, delivering reliable autofocus performance in demanding imaging environments. 

Autofocus enhances throughput, data quality, and system robustness. Whether you need high-speed simplicity or advanced optical control, WDI’s PFA-LN and PFA-DT provide proven, high-performance solutions for real-world applications. 

For application-specific guidance, please contact WDI to review your setup and recommend the best configuration.