Takahashi FSQ-106EDX4 Apochromatic Refactor OTA

The astrophotographers see in the FSQ-106ED one of the best astrographes available for the amateur astronomers. With its focal length of 530mm, an image circle of 88mm and a photographic field of 9,5¶ø, it acts as teleobjective for most powerful CCD and DSR/DSLR cameras of the market.

Based on a Petzval quadruplet optical design with apochromatic ED glasses, the FSQ-106ED is optimized for wide-field imaging of the deep sky. It offers a flat field, and comes equiped with a built-in camera angle adjuster and an oversized rack-and-pinion focuser. To minimize the size of the optical tube, it includes a retractable dewshield and an important backfocus.

The modified Petzval design of the FSQ-106ED, with the field flattener integrated inside the tube, makes it possible to cover all the photographic formats, from 35mm SLR/DSLR to 6x7 cameras. Its photographic image circle of 88mm of diameter (field of 9,5¶ø) does not have an equivalent on the market of the refractors of 100mm of aperture. CCD users will be able to dream with the use of large sensors without risk of vignetting or loss of definition in edge of field. As it is the tradition inside Takahashi company, the objective is entirely collimatable in order to compensate for the possible mechanical and thermal stresses. A perfect image is at this price.

Optics of exception goes of course with mechanics of exception. To replace the traditional camera angle adjuster, Takahashi integrated an oversized rotative rack-and-pinion focuser in the design of its optical tube. This device offers a perfect rigidity to all the types of photographic assembly, even the heaviest. Voluntarily limited, the rack-and-pinion course is controlled by a double system of focusing including a 1/7 microfocuser.
The optical tube assembly is equipped with a retractable dew shield, to gain in volume.

Resolutely directed towards astrophotography, the FSQ-106ED has very many accessory assemblies including visual ones. It has a 186mm backfocus, which will charm the most demanding users. For examples of assembly, please see system-charts.
Even though this refractor is compact, it is quite heavy (125mm of diameter for a weight of 7 kg). Association with the EM-200 equatorial mount is ideal, including with a guidance system TGM in parallel. Many hardware configurations are available to optimize this astrograph and to turn the astrophotography of the deep sky into a moment of pleasure.

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
Compared FSQ-106ED/FSQ-106 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 7¶æm. 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.