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Takahashi FSQ-106ED optical features

FSQ-106ED optical design

The challenge of any astrographe consists in preserving a perfectly flat field while at the same time the DSR/DSLR and CCD sensors increase by size in an extraordinary way. Takahashi thus chose a modified Petzval quadruplet apochromat, with integrated flattener, in order to cover the largest possible field, while minimizing the geometric aberrations, in particular the curve of field and the astigmatism inherent in Petzval design. From the point of view of the chromatic aberrations, the use of ED glass makes it possible to obtain an exemplary correction. Finally, the result is simply impressive of flatness and image contrast.

Compared FSQ-106ED/FSQ-106 chromatic correction

Takahashi company, top-of-the-range manufacturer, has although decided to use ED glasses as well. Stopping the use of Fluorite, mainly for environmental reasons, didn't mean that optical performances have declined. The most obvious example is the FSQ-106ED, that can be judged by the curves of chromatic correction. The result is outstanding : the new ED formula does even better than its Fluorite ancestor ! Moreover, the correction was widened apart from the visible spectrum to adapt to the new demand of the numerical imaging.

Spot diagrams

The spot-diagrams of the FSQ-106ED are eloquent. The integrated field corrector, perfectly calculated and manufactured, works at its best. At prime focus, at the edge of the field (nearly 44mm of the optical axis), the stars remain sharpened, including on CCD pixels of 7µm. The association of the QE-Reducer (F/3,6 !) , specifically designed for this quadruplet, allows to gain in real field on the wide objects while preserving the initial optical performances.