FL 1.01x Flattener (FSQ-85ED)

The FSQ-85EDX's additional corrector to cover full-frame sensors

With the continuous development of DSLRs and CCD/CMOS cameras, more and more astrophotographers are equipping themselves with imaging systems with large, full-format, small-pixel sensors. This change is a real challenge for conventional refractors, most of whose lenses have been designed to best cover the APS-C format. Although the Takahashi FSQ-85EDX is designed as a Petzval quadruplet, the full-format sensor coverage was not perfect and the edge of the field suffered from a slight astigmatism typical of this optical system. Takahashi offers a dedicated corrector to correct this defect and thus offer results close to those of the FSQ-106ED. The field is perfectly corrected on a diameter of 44 mm. The flattener causes the focal length of the FSQ-85EDX to be slightly increased (by a factor of 1.01x) from 450 mm (F/5.3) to 455 mm (F/5.4).

The flattener has a M72x1 male thread on the telescope side and a M54x0.75 female thread on the camera side. The required backfocus behind the corrector is 56.2 mm. A female thread at the front accepts filters with an M58 thread.

Main characteristics
Image circle diameter 44 mm
Metal back distance 56.2 mm
Input mechanical interface M72x1 thread, male
Output mechanical interface M54x075 thread, female
Backfocus 36 mm
Diameter 80 mm
Total length 41 mm
Weight 200 g

Diagram of the focal point position and threads of the Takahashi FL1.01X field corrector

Spot-diagram of Takahashi FSQ-85EDX refractor with FL1.01X field corrector