Used Takahashi FS102 Doublet-Fluorite Apochromatic Refractor w/Case-UT-12040-SOLD

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Used Takahashi FS102 Doublet-Fluorite Apochromatic Refractor w/Case-UT-12040-SOLD

The FS-102 objective is 102mm aperture, 820mm FL (F8.1 to be exact). It has superb coatings and a high quality, collimatable, temperature compensating cell. The lenses for the FS series were made by Canon-Optron to Takahashi spec’s, like other Takahashi objectives.

The FS-102 shares the same lens design and cell with its larger and smaller siblings, all of which are ~F8 fluorite doublets with the positive fluorite element on the front (hence the ‘FS’ – Front Surface – moniker). This means the lens is a conventional ‘Fraunhofer’ doublet, like a basic achromat, but with fluorite as the crown.

In recent years, Takahashi have brought back a fluorite doublet at this size, but it’s rather different with a fluorite-at-the-back Steinheil design, faster f-ratio (F7.4) and optimised for imaging (hence the ‘D’ for digital tag).

Does fluorite offer a genuine advantage over high-fluoride glass like Ohara’s FPL53 or OK4 (the stuff LZOS make and use)? Possibly. Fluorite is not a glass, it’s a crystalline mineral and it has optical properties that no glass can quite match, including very high transmissivity and low scatter. The FS manual has this to say:

“… the use of multi-coatings further increases light transmission over any ED glass. This makes any fluorite objective brighter than any comparable glass objective …”

Does putting the fluorite at the front make for a worse optic, as some have claimed? I believe not. Check-out the excerpt from the FS manual below.

Independent tests have found the FS-102 to be a true apochromat, whereas ED doublets (think TV-102) often aren’t. Takahashi’s own spot diagrams suggest that the FS-102 is less well corrected at the violet end than the TSA-102 triplet (so less good for imagers), but better in the yellow, orange and red (great for Mars).


Warranty90 Day


  • Takahashi FS102 fluorite optical tube
  • 1.25" diagonal
  • 18mm LE eyepiece
  • Custom foam lined hardwood case


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