Takahashi FCT-L 0.99x Field Corrector

The Takahashi FCT-L 0.99x field corrector flattens the photographic field of the FCT-114DF, FCT-114DS, FC-100DZ, and FC-100DF refractors while changing their focal length only slightly. Its two-element, two-group design provides a 55 mm image circle. It is designed for astrophotography setups that require correction of stars within the field of view while maintaining a focal length close to that of the telescope.

A focal length that has been almost preserved

In the configurations specified by Takahashi, the FCT-114DF and FCT-114DS provide a focal length of 795 mm at f/7.0. The FC-100DZ reaches 791 mm at f/7.9, and the FC-100DF reaches 734 mm at f/7.3. This distinguishes the field corrector from the FCT-L 0.8x reducer: it prioritizes field flattening with minimal focal length variation. The choice between the two accessories therefore depends on the desired photographic setup.

Takahashi reports a relative illumination of nearly 100 % at the edge of the full field of view with the FCT-114DF. It remains at approximately 90 % with the FCT-114DS, whose inner diameter of the sliding tube results in a gradual decrease toward the edges. For both of these eyepieces, the RMS diameter of the spots is specified as 4.4 µm on-axis and 5.8 µm at the edge of the full field of view.

With the FC-100DZ, the illuminance decreases starting from the APS-C area but remains at approximately 93 % at the edge of the full-frame area. The RMS spot diameter is 4.8 µm on-axis and 7.2 µm at the edge of the full-frame sensor. The FC-100DF retains a slight chromatic halo from the lens, despite the correction of stellar images across the field and a brightness of nearly 90 % at the edge of the full-frame area.

Prepare a complete montage

The corrector has two M72 male threads with a 1-mm pitch. It is used with a separate CO ring: CO 114D for the FCT-114DF, FCT-114DS, and FC-100DZ; CO 100DF for the FC-100DF. The assembly also includes the M-series camera rotator and the M72 L52 extension tube. This extension tube is included as standard equipment with the FCT-114D; it must be purchased separately for the FC-100DZ and FC-100DF. Check the parts already present on the telescope and follow the order indicated in the Takahashi diagram.

For a CMOS camera, the appropriate M72-M48 or M72-M54 adapter provides a distance of 55 mm between the base of its camera-side thread and the sensor. Canon EF and Nikon F mounts use the M72 WR adapter with their DX-WR ring. Adapters and connecting rings are sold separately. The use of a filter in the designated slots is subject to Takahashi’s disclaimers regarding stray light 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

• 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.