Like the FS series, the FC series are apochromatic refractors with two-element fluorite lenses.  The FC series have larger apertures and longer focal lengths than the FS series, and provide outstanding performance both for the visual observer and the digital imager.  The FC series has its own dedicated set of reducers and flatteners, and is also able to use some of these accessories from the TOA series. The FC-100DF is optically identical to the DC model, but features an enhanced 2.7 –inch focuser.  It also features a shorter tube length that provides additional back focus for digital imaging applications.  This added back focus allows use of the FC-35RD reducer, which converts the DF to an f/5.4 instrument.