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.
| Characteristic | Takahashi FL1.01X (FSQ-85EDX) field corrector |
| 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