The FS Series Refractors by Takahashi
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Takahashi© was the first manufacturer to make apochromatic telescopes using a fluorite element in the objective. Since the first 90mm fluorite apochromat was introduced in 1977, Takahashi© has developed an extensive line of apochromats using doublet and triplet objectives. The objective lenses of these refractors use man-made fluorite crystal which is made from natural calcium fluorite (CaF2). Now as a result of a production breakthrough which permits the fluorite crystal to be completely hard multi-coated, Takahashi© has been able to finally redesign its fluorite FC series to produce the FS series. The new design places the fluorite element in front of the objective to achieve the maximum color correction and light transmission.

Photo/Visual Uses

The owner of an FS Series telescope possesses and instrument that is capable of a wide variety of photographic and visual applications. The FS Series refractors produce ultra sharp, very high contrast images. Deep sky astrophotos will be ultra sharp and show an astonishing amount of detail. Using one of the optional dedicated reducers with 35mm or meduim format cameras, further enhances the uses of the FS Series refractors.

Color Correction Characteristics of Fluorite

The following diagram compares the color correction characteristics of fluorite, ED glass and BK7. Clearly, fluorite has the superior correction characteristics.

The focal length of the three lenses has been optimized at 820 mm and for the purpose of comparison the focal length of C and F lines has been made equal. Where the reference scale is set at 0, the vertical axis represents the wave length and the horizontal line represents the focal length. Compared to the others, the fluorite shows almost no color aberration over the visible light spectrum (380nm~770nm) with a very slight difference in the focal point. Fluorite is especially good in the shorter wavelength.

read The Fluorite Advantage for more information