PrimaLuceLab SESTO SENSO 3 LS Robotic Focusing Motor for Telephoto Lenses

SESTO SENSO 3 LS: Robotic Focusing for Telephoto Lenses

Designed and manufactured in Italy, the SESTO SENSO 3 LS brings high-precision automated focusing to camera lenses from brands like Canon and Nikon. It builds on the SESTO SENSO 3 technology, with all control electronics in one chassis and the ports on the side. Its Lens Gear Clamp drives the lens focus ring without external belts; PrimaLuceLab offers a belt as an option for lenses with very stiff focus mechanisms.

Lens Gear Clamp (LGC): Backlash-Free Focusing Without Belts

The Lens Gear Clamp (LGC) is a custom mechanical interface: a rubber drive wheel engages the lens's manual focus ring, and a spring keeps it pressed against the ring for consistent traction. The coupling is backlash-free.

• Spring preload: If the arm angle is wrong, the wheel may not press on the ring, causing slippage, so the manual has you preload the spring during installation.
• Two rubber wheels: The standard wheel comes pre-installed; the narrower 6 mm wheel is for focus rings typically thinner than 18 mm. Pull the standard wheel off its shaft and press the 6 mm wheel on until fully seated.
• Arca-Swiss Mounting: The supplied Arca-Swiss clamp attaches the motor to a PLUS Vixen-style dovetail bar (sold separately), or to another bar with an Arca-Swiss profile on top.

Integrated Encoder: Manual Override with 2 Million Step Resolution

The SESTO SENSO 3 LS has a 2 million step motor and an integrated high-resolution position encoder. With the motor powered on, you can still turn the rubber drive wheel by hand and the system tracks the movement without losing position. The manual recommends always focusing by rotating the drive wheel and not touching the lens focusing ring directly: forcing the ring without turning the wheel can lose position tracking and need a new calibration. Set the camera and lens to manual focus (MF) and do not use autofocus once the motor is installed.

The Automatic Position Recovery function, if enabled, moves the focus back to the previous position if it is rotated manually or accidentally shifted, after a delay you set from 0 to 20 seconds. The encoder detects motor shaft movements only and cannot account for slips inside the lens focusing mechanism.

Wired & Wireless Control: USB-C, WiFi, and PLAY Software

Connect it to an EAGLE computer or a Windows 10/11 PC through the USB-C port with the included cable, for control from PLAY or ASCOM software. Without a computer, use the built-in WiFi and the Virtual HandPad on a smartphone or tablet.

• PLAY Software: PrimaLuceLab's software for calibration, focusing (including autofocus), advanced settings and firmware updates.
• ASCOM Driver: The provided ASCOM driver (tested with ASCOM platform 7) lets third-party software control it; the manual covers Sequence Generator Pro, N.I.N.A. and MaxIm DL. Only one program can connect at a time.
• Virtual HandPad: Join the motor's own WiFi network from a smartphone or tablet and open the Virtual HandPad in the browser to move the focus and save positions.
• ARCO port: Powers and controls an optional ARCO camera rotator through a single cable.

12V Power and EAGLE Computer Integration

The SESTO SENSO 3 LS requires an external 12V supply; USB alone is not enough. Maximum consumption is 800mA at 12V, through a 5.5/2.5mm center-positive port. The package includes a cigarette-lighter plug cable for a 12V battery.

With a PrimaLuceLab EAGLE computer, an optional cable powers the SESTO SENSO 3 LS directly from the EAGLE. GHOST mode lets the EAGLE operate it without a USB cable, and DARK mode dims or turns off the LEDs.

Automatic Focus Compensation for Temperature Changes

Temperature changes during the night make focus drift. The SESTO SENSO 3 LS has an internal sensor that reads the motor temperature and a port for the optional external temperature probe, which focus temperature compensation requires.

With the probe connected, you calibrate in PLAY by recording at least 3 focus points with a temperature difference of 5°C. Once enabled, the compensation applies with PLAY and with third-party software through the PLL ASCOM Focuser driver.

Installation and Alignment on Your Lens

First fit a PLUS Vixen-style dovetail plate under the lens's L-shaped tripod collar (the 240mm PLLVIX240P is a good choice, depending on the lens). Loosen the four set screws, rotate the LGC arm and fit the Arca-Swiss clamp to the motor's side support with the M4 screw, at the outer end of the slot. Lock the motor onto the plate and slide it until the rubber drive wheel is centered on the focusing ring. Rotate the arm until the wheel touches the ring, tighten the set screws, then slide the motor a few millimeters toward the lens to preload the spring and lock the clamp screw.

For lenses without an integrated L-shaped tripod collar, the optional "Camera support for SESTO SENSO 3 LS" (PL8410094) fits under the camera body with a 1/4"-20 screw and locks onto the plate. On lenses with the focusing ring toward the front, such as the Canon RF 100-500mm f/4.5-7.1, the motor mounts in a mirrored position on the camera side of the plate.

Calibration and Compatible Lenses

Photo lenses vary in focusing range and infinity position, so calibration tells the SESTO SENSO 3 LS where the focus ring currently is. Point the camera at stars, the Moon or a planet, set the lens to manual focus, bring it to rough focus while checking live view, then press CALIBRATE in PLAY. Disconnect and reconnect the USB and power cables, and reconnect in PLAY. Compatible lenses include (not limited to these):

• Nikkor Z 70-200mm f/2.8 VR S, Nikkor Z 100-400mm f/4.5-5.6 VR S
• Nikkor Z 24-120mm f/4 S, Nikkor Z 24-70mm f/4 S, and other telephoto lenses with a manual focus ring

For telescopes, PrimaLuceLab makes the SESTO SENSO 3 and the SESTO SENSO 3 SC.