Starlight Instruments Feather Touch 3.5" R&P Focuser

The Feather Touch 3.5": For 18-20 Pound Imaging Payloads

Engineered for astrophotographers and demanding visual observers using large telescopes, the Feather Touch 3.5" focuser is defined by its immense load-bearing capability. It is rated at 18-20 pounds, so camera, filter wheel and other accessories can hang from the drawtube within that figure.

Check clearance before you order: the telescope must have at least 4.35" of clearance for the drawtube to go inside the telescope; otherwise the drawtube will bottom out before reaching its full inward travel.

The Helical Rack & Pinion: Heart of the 3.5" Drive System

At the core of the focuser's strength is its helical rack and pinion drive. This system provides a positive, geared connection between the focus knobs and the 3.5" drawtube, ensuring smooth motion with virtually zero backlash. The helical rack and pinion gives smoother operation and increased carry loads.

The rack sits on the underside of the drawtube and the pinion assembly on the underside of the focuser; both ship with a thin film of grease and need no further lubrication.

1.375" and 4.5" Travel: Options for Refractors & Reflectors

The Feather Touch 3.5" is offered in two drawtube travel lengths to suit different telescope designs and applications. The 1.375" (34.93 mm) travel version is known to fit large RC and Dobsonian scopes. With the standard adapter and 2" compression ring end cap it weighs 5.216 pounds and measures 5.236" racked in and 6.625" racked out from the mounting face.

The 4.5" (114.30 mm) travel version is known to fit large refractors. With the standard adapter and 2" compression ring end cap it weighs 5.938 pounds and measures 5.236" racked in and 9.736" racked out from the mounting face.

The 10:1 Planetary Reduction Assembly for Critical Focus

The 10:1 reduction assembly gives the fine control. This friction-based planetary system translates ten full turns of the fine-focus knob into a single turn of the coarse-focus knob, allowing for extremely precise adjustments. The assembly has a stainless steel housing, high grade stainless steel ball bearings in a brass cage and a tool steel reduction pin; its operation is smooth, with virtually zero backlash.

For added control, a brake thumbscrew on the pinion assembly locks the drawtube in place to prevent any unwanted movement. Minor adjustments with the fine focus knob are possible after locking, but prolonged use with the brake engaged may wear the internal brake component prematurely.

Full 360° Rotation for Perfect Target Framing

For imagers, composition is key. The Feather Touch 3.5" incorporates a 360-degree rotating locking collar that allows you to orient your entire camera and accessory package to perfectly frame your target. Whether you are capturing the full expanse of the North American Nebula (NGC 7000) or aligning your frame with the galactic plane, you can achieve the ideal orientation without ever loosening the camera in its adapter.

To operate, you simply turn the locking collar counter-clockwise to release the tension, rotate the focuser body to the desired angle, and then tighten the collar clockwise to lock it securely. Starlight applies a dampening grease between the focuser and the tube adapter, so the focuser should not be separated from the adapter unless necessary.

A Modular System: 5.125" Adapter Threads & Custom End Caps

It connects to your telescope through a tube adapter (sold separately); the locking collar has 5.125x24 female threads. In most cases the adapter screws onto the telescope; on some (such as carbon fiber tubes) it is secured with screws.

On the visual side, the drawtube has a 4 3/32x24 TPI thread for end caps (sold separately). The most common is the 2" compression ring; threaded end caps give a more secure connection for reducers, cameras and other accessories.

The 3.5" Drawtube: Millimeter Scale & Internal Baffling

For repeatable focus positions, a millimeter scale on the side of the drawtube lets you return to a known focus point when changing filters or sessions.

Inside, the drawtube is treated with glare-resistant black baffling. This feature minimizes internal reflections and stray light, which is essential for maximizing contrast.

User Adjustments: 3-Point Collimation & Tension Control

To ensure perfect optical alignment, most end caps for the Feather Touch 3.5" feature three set screws for collimation adjustment. Loosen them with a 1/16 hex key, unscrew the end cap about 1/4 turn, adjust the tilt, then tighten the same screws.

Additionally, a drawtube tension nut lets you control the drag or feel of the drawtube's movement. It takes a 3/16 hex key; a second tension nut hidden by the adapter is factory set and should not be adjusted. Keep at least light tension on the drawtube to prevent drawtube tilt and image shift.

Automation Ready: Integrating Starlight HSM & PDMS Motors

The Feather Touch 3.5" focuser is designed for seamless integration into a fully automated imaging setup. The pinion assembly allows for the attachment of Starlight Instruments' motor systems (sold separately), the HSM35 Handy Stepper Motor, which fits any 3.5" Feather Touch focuser, or the belt-driven Posi Drive Motor System (PDMS); the PDMS has a version for 3.5" Feather Touch focusers.

Paired with a controller like the Focuser Boss II, these motors enable precise, repeatable focusing controlled by a computer. ASCOM clients can then drive the focuser; Starlight's EFS controller adds backlash correction and temperature compensation.

Built to Last: #8-32 Mounts & USA-Machined Construction

Every Feather Touch focuser is designed, machined, anodized, and assembled in-house at Starlight Instruments' facility in the USA. The body is constructed from hardened stainless steel, steel, and anodized aluminum .

Practical design elements include two sets of #8-32 threaded holes on the focuser housing for attaching a finderscope bracket. Filler screws sit in the holes until used; with third-party bases, use screws that are not too long or they can damage the drawtube.

Installation in 3 Steps: Attach, Orient, and Collimate

Installing the Feather Touch 3.5" is a straightforward process. After removing your telescope's stock focuser, you begin by attaching the Feather Touch tube adapter to the telescope; in most cases it simply screws into place.

Next, you secure the focuser to the adapter, loosen the locking collar, and rotate the focuser into your desired orientation before locking it down. Finally, if necessary for your imaging train, you can perform a final collimation adjustment using the three set screws on the end cap if necessary.

This product is sold as the focuser body only. A telescope-specific tube adapter and an accessory end cap must be purchased separately to match your equipment.