Takahashi FC-100DZ Fluorite Refractor

The FC-100DZ is a fluorite doublet with a 100 mm aperture and an 800 mm focal length.   In this doublet design, Takahashi has paired the fluorite element with a low dispersion glass having a high refractive index.  This combination provides excellent optical performance across the entire visible spectrum with a Strehl ratio in excess of 97.6% across this range.  In addition, to satisfy the increasing demands of today’s imaging system, this glass combination minimizes the blue halo sometimes present at shorter wavelengths.  This halo intensity is reduced by about 50% when compared to the existing FC-100D.