Starlight Instruments Feather Touch Micro Focuser for Celestron CPC800/RASA 8", NexStar 6SE, C8Edge HD 8SE SCT and Sky-Watcher 150/180mm Mak

FTM-CPC8: A 10:1 Dual-Speed Upgrade for Celestron and Sky-Watcher

This Feather Touch Micro Focuser is not a new focuser; it upgrades the knob that drives your telescope's primary mirror focus. It replaces the single-speed knob with a two-speed assembly: a black coarse knob and a brass fine knob at a 10:1 ratio, so ten turns of the fine knob equal one turn of the coarse knob.

Fine control helps most on long focal length Schmidt-Cassegrains and Maksutovs, where the zone of sharp focus is shallow. On Celestron telescopes, this "CPC" version is for a triangular pattern on the back cell.

How It Works

SCTs and Maksutovs focus by moving the primary mirror along the baffle tube. The Micro Focuser threads onto the telescope's focus shaft through a brass stop, which also keeps the mirror from falling off the baffle tube, so it still moves the mirror and does not remove image shift.

You use the coarse knob for large focus changes and switch to the 10:1 fine knob as you approach focus, so you can reach focus without the coarse jumps of the stock knob.

The Critical Focus Zone

A telescope's critical focus zone (CFZ) is the small range where the image is sharp, and on a long focal length Schmidt-Cassegrain or Maksutov it is shallow. The coarse motion of a standard focuser knob can easily move the mirror past this zone in a single, small turn, making it frustratingly difficult to hit and hold perfect focus.

The 10:1 fine knob lets you make deliberate, small movements, which helps on planetary and lunar detail and close double stars.

Compatibility Check: Is the FTM-CPC8 Right for Your Telescope?

Check before ordering:

• Celestron Back Cell Style: If your telescope is less than a few years old, the back cell shows the version: a triangular pattern needs this "CPC" version, and a flat back needs the standard "C" version.
• NexStar 6SE Flange Measurement: If you own a Celestron NexStar 6SE, you must perform an additional check. Celestron has used two different flange sizes on the stock focuser for this model. Measure the outside diameter of the flange of the stock focuser, the part that mates to the rear cell: 1.5″ (38mm) or 1.6″ (40.6mm). The FTM-CPC8 fits the 1.6″ (40.6mm) flange; a 1.5″ (38mm) flange needs Starlight's FTM-C6 instead.
• Starlight's list: Celestron CPC-800, RASA 8", NexStar 6SE / 8SE and C8 EdgeHD (with triangular back), plus the Sky-Watcher 150mm and 180mm Maksutovs. Starlight links third-party installation instructions for the Sky-Watcher SkyMax 150mm Maksutov.

FTM-CPC8 vs. the Stock Knob

Both act on the same internal focus shaft.

• Stock knob: a single speed.
• Feather Touch FTM-CPC8: A dual-speed system with a 10:1 fine-focus ratio. Ultra-smooth coarse and fine knobs and an ultra-low backlash system are among the Feather Touch standard features. It does not remove image shift from the moving mirror.

Installation in Nine Steps

Position the optical tube horizontally before removing the original focus assembly, or the primary mirror could move. Starlight's instructions are written for the CPC-800.

1. Remove the Rubber Knob: Pull the original rubber focus knob off the brass focus cylinder.
2. Remove the Cover: Unscrew the 3 small Phillips-head screws and remove the focus assembly cover plate.
3. Expose the Shaft End: Turn the brass part of the assembly clockwise to move the mirror and expose the end of the threaded focus shaft.
4. Remove C-Clip or Screw: Carefully remove the small C-clip or Phillips-head screw from the tip of the focus shaft. Keep this part for reinstallation.
5. Remove Bearing Assembly: Rotate the brass cylinder counterclockwise until it unthreads from the focus shaft; this takes quite a few turns.
6. Install Brass Stop: Unthread the brass stop from the new MicroFocuser and thread it onto the telescope's focus shaft until the end of the shaft is exposed.
7. Reattach C-Clip or Screw: Snap the C-clip back into its groove on the shaft tip or reinstall the screw and washer.
8. Attach the MicroFocuser: Thread the MicroFocuser body onto the installed brass stop. Hold the stop with a wrench and the black knob with your other hand to tighten it; the stop must be tight. Thread the focuser down until its base sits flush with the back of the telescope, pushing it forward to move the mirror if needed.
9. Mount the Focuser: Use the three provided M3 hex-head screws and wrench to attach it. The telescope will likely be far out of focus at first.

Parts and Tools

Starlight's parts list and tools:

• Included with the FTM-CPC8: The Feather Touch SCT MicroFocuser assembly, three M3-0.5x10 hex-head screws for mounting, and a 2.5mm hex-head wrench.
• Tools You Will Need: A Phillips screwdriver to remove the stock focuser cover and a ½” or adjustable wrench to tighten the brass stop during installation.

Motorizing Your FTM-CPC8: The HSM20 Stepper Motor Upgrade

The HSM20 fits any Feather Touch Micro Focuser, so you can add computer-controlled focusing later.

The specific motor for this focuser is the Handy Stepper Motor (HSM20), which fits any Feather Touch Micro Focuser. The HSM20 and a Focuser Boss II or EFS controller are sold separately; the controllers work with ASCOM software.

Made in the USA

Starlight Instruments designs, machines, anodizes and assembles its Feather Touch components in-house in the USA. The brochure lists durable hardened stainless steel, steel and aluminum construction and an anodized aluminum fine focus knob among the Feather Touch standard features.