Takahashi FCT-L CO 100DF Adapter for Reducer and Corrector

The Takahashi FCT-L CO 100DF ring is designed for use with the FC-100DF telescope when it is equipped with the FCT-L 0.8x focal reducer or the FCT-L 0.99x field corrector. It provides the spacing specified by the manufacturer for this optical system. This adapter is selected based on the telescope and is then combined with the converter and camera interface indicated in the corresponding assembly diagram.

The FC-100DF's unique optical path

Takahashi specifies an optical path length of 23 mm for the CO 100DF. This length differs from that of the CO 114D, which is reserved for the FCT-114DF, FCT-114DS, and FC-100DZ. Both rings use the same type of thread, but the manufacturer recommends using the version specific to the instrument to maintain the correct spacing and correction. For an FC-100DF, therefore, the CO 100DF is the one specified in the documentation.

The connectors are M72 female with a 1-mm pitch, on both the eyepiece side and the camera side. In both FCT-L diagrams, the ring is located after the converter and before the camera adapter. The reducer and corrector have M72 male threads. This arrangement distinguishes the CO ring—which is part of the FC-100DF’s optical configuration—from the final adapter chosen for the camera body’s thread or mount.

Connection to a camera or housing

CMOS cameras use the M72-M48 or M72-M54 adapter corresponding to their mechanical mount. Takahashi specifies a distance of 55 mm between the base of the camera-side thread on this adapter and the sensor plane. The 23-mm optical path of the CO ring is a separate specification: the reference point for camera back focus is that of the final adapter.

Canon EF and Nikon F camera bodies follow the other branch of the diagram, using the M72 WR adapter and the DX-WR wide-angle ring designed for their mounts. The telescope-side assembly includes the M camera rotator. When using the FCT-L 0.99x field corrector on the FC-100DF, the M72 L52 extension tube is also required. These components must be identified separately when setting up the photographic train.

The CO 100DF has a diameter of 76 mm, a length of 23 mm, and a weight of 37 g. The documentation specifies that this ring is sold separately from the reducer and the corrector. Its function remains the same with both converters: to provide the connection and spacing required for the FC-100DF. Selecting this ring and following the diagram are the first steps in the assembly process, before adjusting the camera connection.

Technical specifications

Compatible glasses in the catalog

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

Technical Documentation

• 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

• FCT-L 0.8x Focal Length Reducer, sold separately.
• FCT-L 0.99x Field Corrector, sold separately.
• M72 Male to M48 Male Adapter for M48 CMOS Camera, sold separately.