Takahashi FCT-L 0.8x Focal Reducer

The Takahashi FCT-L 0.8x focal reducer is designed for astrophotography with the FCT-114DF, FCT-114DS, FC-100DZ, and FC-100DF refractors. Its three-element, two-group optical design shortens the focal length while correcting stellar images within a 44-mm image circle. It allows for a more open photographic system, with particular attention paid to star shape and field illumination.

A configuration tailored to each pair of glasses

With the FCT-114DF and FCT-114DS, Takahashi announces a focal length of 639 mm at f/5.6. The FC-100DZ reaches 636 mm at f/6.4, while the FC-100DF operates at 587 mm at f/5.9. These values correspond to the specifications provided by the manufacturer. Compatibility depends on the entire mounting assembly, including the CO ring designed for the telescope and the adapter for the camera.

Choosing the right ring is essential: the FCT-L CO 114D is compatible with the FCT-114DF, FCT-114DS, and FC-100DZ, while the FCT-L CO 100DF is designed for the FC-100DF. These rings, sold separately, have different optical path lengths. The adapter uses an M72 male thread with a 1 mm pitch on each side. Installation also requires the M-series camera rotator, in accordance with the Takahashi diagram.

Stellar Luminosity and Quality

At the edge of full format, the reported relative illumination is approximately 92 % with the FCT-114DF, 83 % with the FCT-114DS and the FC-100DZ, and 82 % with the FC-100DF. For the FCT-114D models, the RMS spot diameter is 4.4 µm on-axis and 6.6 µm at the edge of the full-frame area. The FC-100DF retains a slight chromatic halo from its lens; the reducer therefore does not completely eliminate this optical characteristic.

Connecting the Camera

For a CMOS camera, select the M72-to-M48 or M72-to-M54 adapter that matches its connection. The sensor must be positioned 55 mm from the base of the thread on the camera side of this adapter. For a Canon EF or Nikon F camera body, the setup uses the M72 WR adapter and the appropriate DX-WR ring. These components are separate from the step-down adapter. The diagram also calls for the use of filters, with a caveat from the manufacturer: they may cause unwanted reflections and vignetting.

Technical specifications

Compatible glasses in the catalog

• Takahashi FCT-114DS – 114 mm fluorite telescope, tube only
• Takahashi FCT-114DF – 114 mm fluorite telescope, tube only
• Takahashi FC-100DZ – 100 mm fluorite telescope with finder scope and mount
• Takahashi FC-100DZ – 100 mm fluorite telescope, tube only
• Takahashi FC-100DF – 100 mm fluorite telescope with finder scope and mount
• Takahashi FC-100DF – 100 mm fluorite telescope, tube only

Technical Documentation

• FCT-L 0.8x Reducer Manual by Manuel Takahashi (PDF)
• Takahashi Installation Diagram for the FCT-L Gearhead (PDF)
• Takahashi Installation Diagram for the FCT-L Corrector (PDF)
• Takahashi Technical Presentation on the FCT-L Reducer and Corrector (PDF)

Takahashi's Official Presentation of FCT-L Accessories

Selecting the elements for the montage

• CO 114D, for FCT-114DF, FCT-114DS, and FC-100DZ, sold separately.
• CO 100DF, for FC-100DF, sold separately.
• M72 male to M48 male, for connecting an M48 CMOS camera, sold separately.