Optec TCF-Leo Low Profile Focuser

The Low-Profile Solution: Just 31.8 mm of Back-Focus

Engineered for telescopes where every millimeter of back-focus is critical, the TCF-Leo is very thin. At its fully inward position, the focuser body is only 31.8 mm (1.25 in) thick, expanding to just 40.6 mm (1.6 in) at full extension. At the midpoint of its travel, it occupies a mere 36.2 mm of the optical path, preserving precious back-focus for filter wheels, off-axis guiders, and large camera bodies.

Despite its slim design, the TCF-Leo features a true 3-inch drawtube, providing a clear aperture of 76.2 mm.

Mechanical Precision: 8.9 mm of Travel at 0.08 µm Resolution

The core of the TCF-Leo is a stepper motor drive system that delivers fine focus adjustments. The focuser offers a total travel range of 8.9 mm (0.35 in), divided into 112,000 individual steps. This translates to an exceptionally fine step resolution of 0.08 µm.

Start each session at the center position (56,000 steps) and reach rough focus with the telescope's own focus knob or spacer rings, so that normal focus falls within the 8.9 mm of travel.

Dual-Mode Payload Capacity: 9 kg Hi-Torque or 5 kg Hi-Speed

The TCF-Leo's performance can be optimized for your specific imaging train through two distinct software-selectable modes. The trade-off is direct: higher torque for heavier loads, or higher speed for faster adjustments.

• Hi-Torque Mode: Optec's recommended setting for heavy imaging trains: it reliably handles payloads up to 9 kg (20 lb) at speeds up to 1,400 steps per second.
• Hi-Speed Mode: If you prefer faster movement, this mode reaches 2,400 steps per second and the focuser typically homes in under a minute. The recommended maximum payload drops to approximately 5 kg (11 lb).

System Integration: OPTEC-3600 and OPTEC-3000 Adapter Standards

Optec utilizes a standardized adapter system to ensure rigid, secure connections throughout the imaging train. The TCF-Leo is built around these established interfaces for broad compatibility.

The telescope side of the focuser uses the OPTEC-3600 dovetail mount, Optec's 3.6-inch standard, with a line of OPTEC-3600 telescope adapters sold separately (for example #17803 for the Celestron EdgeHD C-11 and C-14). On the camera side, the focuser features a 3-inch bore designed to accept any OPTEC-3000 series adapter, allowing you to connect to T-threads, 2-inch accessories, and other common imaging interfaces.

The FocusLynx Hub: Centralized Focuser Control

The FocusLynx hub (included in the With FocusLynx Hub version) runs the TCF-Leo. It connects to a PC via USB/Serial or Ethernet, allowing for remote operation from inside your observatory or home network. The hub is powered by a standard 12 VDC supply.

The FocusLynx system is also expandable. Optional upgrades allow you to add a second focuser control board, an 802.11 WiFi module for wireless control, and a physical hand controller for tactile, vibration-free focusing at the eyepiece.

Universal Software Support: FocusLynx Commander, ASCOM, and Alpaca

Optec provides a comprehensive software suite to control the TCF-Leo on modern operating systems. The FocusLynx Commander software for Windows 10 and later offers a complete graphical interface for all focuser functions, including setup, temperature compensation, and manual control.

For autofocus software such as Maxim D/L, TheSky X, SGP or FocusMax, the TCF-Leo is supported by ASCOM and Alpaca drivers. The Alpaca driver extends compatibility to Linux-based systems, ensuring the focuser can be controlled by a wide range of observatory platforms and single-board computers.

Automated Focus: Temperature Compensation with the Included Probe

As ambient temperature drops during an imaging session, a telescope's optical tube contracts, causing the focal point to shift. The TCF-Leo addresses this with a precision digital temperature probe (included in the With FocusLynx Hub version). This probe attaches to your telescope's tube to provide real-time thermal data directly to the FocusLynx hub.

Using the Temperature Compensation Wizard in FocusLynx Commander, you can determine your telescope's unique temperature coefficient (TC). Once enabled, the controller will make continuous, minute adjustments to the focuser position throughout the night, keeping focus as the temperature changes.