Wireless Follow Focus Product

Overview

Follow focus systems automate lens focus during video production, allowing a dedicated operator to maintain sharp focus on a moving subject while the camera moves or changes aperture. This wireless variant gives the focus puller freedom of position, eliminating cable tether constraints on set. The system comprises a hand-held transmitter with a focus wheel encoder, a wireless receiver mounted near the camera lens, and a brushless motor that engages the lens's focus ring via friction coupling.

Unlike manual focus pulls (where the operator rotates the focus ring directly on the lens), motorized follow focus decouples the operator's hand position from focus position, enabling precise remote control and repeatable focus racks across multiple takes. Absolute position feedback from the receiver motor allows the transmitter to display live focus distance, essential for planning focus marks during rehearsal.

How it works

The system operates across three interconnected domains: RF communication, motor control, and mechanical coupling.

Wireless Link

The hand transmitter encodes focus wheel rotation as serial encoder counts. The STM32L0 microcontroller in the transmitter samples the Encoder every 10 milliseconds, computes the delta (incremental rotation), and transmits a 32-byte packet via the RF Module TX nRF24L01 transceiver. The TX Antenna radiates this at 100 mW across a 50-meter range in open air.

The receiver RX Antenna captures the packet. The RF Module RX nRF24L01 forwards it to the STM32F0 MCU, which decodes the encoder delta and calculates the required motor velocity.

Motor Actuation

The receiver drives the Brushless Motor (8000 RPM BLDC) via the BLDC Driver IC, a three-phase commutation driver feeding coil current through FETs. The Planetary Gearbox (10:1 planetary reducer) steps down speed to ~800 RPM, yielding high torque at the output shaft. This geared output drives the Output Drive Wheel, a 30 mm silicone-coated friction wheel that grips the lens's focus ring.

The Encoder on the receiver motor shaft (absolute multi-turn type) feeds position feedback to the MCU via I2C. The microcontroller transmits this position back to the hand transmitter at 5 Hz, updating the focus marking ring display.

Mechanical Coupling

The Motor Head Assembly assembly mounts to the camera rig via dual Rod Mount System on 15 mm aluminum support rods. This architecture allows the motor head to be repositioned without tools, and the silicone friction wheel accommodates focus rings of differing diameters by simply advancing the clamp until light contact is made. Tightening the clamp lever locks the position. The motor rotates the wheel, which in turn rotates the lens focus ring directly.

Focus Marking and Pre-focus

Before rolling, the focus puller uses the hand transmitter's Focus Marking Ring to mark expected focus distances. The motor advances to each mark position, and the puller records the corresponding encoder position on paper. During the take, pulling the hand wheel to each marked position ensures precise focus at each cue.

Live feedback from the receiver's absolute encoder is transmitted back to the transmitter MCU and displayed on the Focus Marking Ring index pointer, so the focus puller always knows the current focus distance without looking at the camera.

Power Budget

The hand transmitter draws approximately 40 mA during transmission bursts and 20 mA idle (MCU + RF module standby). Two AA cells (3000 mAh nominal) yield 50–60 hours of operation in a typical 8-hour shooting day, requiring one battery swap per day.

The receiver draws 800 mA under load (motor at rated current) and 200 mA idle. A single 18650 lithium cell (2500 mAh) provides 3–4 hours of continuous motor operation, or 8–12 hours in a typical shoot (intermittent focus pulls with long idle periods between takes). USB charging via the integrated Lithium Charger takes 4–6 hours from empty.

Lens Compatibility

The friction wheel approach works with virtually all cinema-grade lens focus rings, from wide-angle (manual-focus cinema lenses like Zeiss Master Primes) to telephoto designs. Independent gearbox ratio tweaks accommodate focus rings with different friction coefficients. Very light-torque focus rings on some autofocus lenses may slip; the system recommends manual focus engagement or locking autofocus and using manual override.

Set Deployment

The motor head clamps to the camera's existing 15 mm rod rails in under 30 seconds. The receiver module mounts on a hotshoe adapter or 1/4"-20 screw on the camera body. Power connections (12V to motor, 3.3V to RF) are internal. The hand transmitter is pocketed; a coiled tether is optional for safety in moving vehicles or elevated rigs, but the wireless link requires no physical connection.

Latency and Smoothness

The nRF24L01 transceiver achieves 2–4 millisecond packet latency over the air. Motor commutation introduces another 1–2 ms lag. Total focus ring response latency is 4–8 ms, imperceptible to human operators and invisible in video playback. This makes the system feel like a direct mechanical linkage.

Limitations and Maintenance

The friction wheel method is non-invasive but not ideal for rapid focus racks above 2 focus ring rotations per second; slip becomes noticeable at high speeds. The silicone wheel is consumable, requiring replacement every 500–1000 focus pulls depending on focus ring surface condition.

The brushless motor is efficient and requires no brush maintenance. The planetary gearbox is sealed and lubricated at factory, requiring no user service. Wireless range is reduced by steel or aluminum set structures; range testing on location is recommended.