The classic Petzval design of the Takahashi FSQ was sufficient to offer high-end optical performance with APS-C format cameras. Central aberration was corrected and peripheral field curvature contained. But with the advent of small-pixel, full-format sensors, the existing QE0.73x reducer was showing its limitations. Takahashi therefore decided to modernize the specific reducer of its FSQ-85EDX astrograph to adapt it to the constraints of the digital sensors currently on the market, thus restoring its full astrophotographic potential.
The revision of the 0.73x reducer on the Takahashi FSQ-85EDX is the logical follow-up to the introduction of the 1.01x field corrector, whose aim was to enable the astrograph to cover full format perfectly. With the QB0.73x reducer, field curvature is improved and focal length is reduced by almost a quarter, to 330 mm (F/3.9).
The reducer uses a new, highly refractive and low dispersion ED glass. It is composed of 4 lenses in 2 groups. Chromatism is further reduced, and the size of the RMS spot at the edge of the field is halved, reducing the size of the stars by a third. At the center, the spot radius is 1.6 microns RMS, 1.9 microns at the APS-C format periphery and 3.9 microns at the APN format limit. With these performances, the FSQ-85EDX confirms its reputation for excellence in astrophotography, even when combined with today's full-frame digital sensors.
The QB0.73x reducer screws directly onto the CAA (Camera Angle Adjuster).
The mechanical backfocus of the corrector is 72.2 mm and the output thread is M56x0.75 male. To recover the 56.2 mm required for mounting a wide-field T-ring and camera, it is imperative to use the CA-35 photo adapter (SKY-90, #TATKA35201) at the reducer output.
A ZWO camera is mounted in the same way, using the CA-35 (SKY-90). To recover the input threads of ZWO accessory trains (M48 or M42 threads), you'll need to use the OU073 conversion ring specially designed by Optique Unterlinden.
| Characteristic | Takahashi QB0.73X focal reducer |
| Item number | TKA37580 |
| Optical design | 4 lenses (2 groups) |
| Corrected image circle | 44 mm |
| Input mechanical interface | M72x1 thread, male |
| Output mechanical interface | M56x0.75 thread, male |
| Metal back distance | 72.2 mm |
| Size | 78 mm x 63 mm |
| Weight | 520 g |
| System-chart of Takahashi FSQ-85EDX refractor with QB0.73X (2023) | Download |