Focal reducer Takahashi RD-QB 0.73x (18B) for FSQ-85EDX
Petzval's classic design of the Takahashi FSQ tubes was sufficient to provide high-end optical performance with APS-C format shooting systems. Central aberration was corrected and field curvature in the periphery was contained. But with the emergence of full-frame sensors with small pixels, the existing reducer, the QE0.73x model, shows its limits.
Therefore, Takahashi decided to modernize the specific focal reducer of its FSQ-85EDX astrograph to adapt it to the limitations of the digital sensors currently offered on the market, thus recovering its full astrophotographic potential.
The revision of the 0.73x reducer of the Takahashi FSQ-85EDX refractor is the logical continuation of the appearance of the 1.01x field corrector whose objective was to allow the astrograph to perfectly cover the entire format.
With the QB0.73x reducer the field curvature is improved and the focal length is reduced by almost a quarter; the focal length increases to 330 mm (F/D 3.9).
Aspect of the center and 4 corners of an image taken with a ZWO ASI2600MC Pro camera associated with the Takahashi FSQ-85EDX telescope equipped with the QB0.73x reducer.
The reducer uses a new ED glass, highly refractive and with very low dispersion. It consists of 4 lenses divided into 2 groups. The chromatism is further reduced and the RMS spot size at the periphery of the field is halved, reducing the size of the stars by one third.
In the center, the spot radius is 1.6 microns RMS, 1.9 microns at the periphery of the APS-C format and 3.9 microns at the edge of the APN format. With these performances, the FSQ-85EDX confirms its reputation for excellence in astrophotography, even when combined with today's full-frame digital sensors.
Assembly
The QB0.73x reducer screws directly onto the rotating frame collar located at the exit of the FSQ-85EDX viewfinder Takahashi.
The mechanical backfocus of the corrector is 72.2 mm and the output thread is in M56x0.75 male format. To recover the 56.2 mm needed to mount a wide-field T-ring and a camera, it is essential to use the CA-35 photo adapter (SKY-90, ref. TATKA35201) at the output of the reducer.
The mounting of a camera ZWO is done in the same way, using the CA-35 (SKY-90). To recover the input threads of the accessory train ZWO (M48 or M42), it must pass through the conversion ring OU073 specially designed by the distributor.
Mounting a camera box behind the reducer Takahashi QB0.73x for FSQ-85EDX
Focal reducer Takahashi RD-QB 0.73x (18B) for FSQ-85EDX
