William Optics ZenithStar ZS61 II OTA — 61 mm doublet apochromat This refractor provides a 360 mm focal length at f/5.9. The manufacturer lists a 45 mm image circle and optional correctors for photographic use.
Manufacturer model: William Optics ZenithStar ZS61 II OTA · Specifications checked against manufacturer data on 2026-11-03
This refractor provides a 360 mm focal length at f/5.9. The manufacturer lists a 45 mm image circle and optional correctors for photographic use.
The 2-inch rack and pinion focuser provides 75 mm travel. Connections comprise M54 to 2-inch visual back; 2-inch to 1.25-inch visual back.
Manufacturer-listed options: Flat61A 1.0x, Flat61R 0.8x. Each combination has a specific spacing and adapter arrangement; see the individual settings in the specifications. A corrector is an optional accessory.
Tube length is 245–315 mm and OTA weight is 2.2 kg.
William Optics manufacturer manual
The objective uses Ohara FPL-53 ED glass for colour correction. The manufacturer lists a dual-sided Vixen / Arca-Swiss dovetail for mounting. For photographic use, select the correct flattener or reducer and its specified adapters; telescope focal length and corrector spacing are separate specifications.
Prime-lens telescope: corrector compatibility and spacing are model-specific. Optional correctors are listed, not assumed included; corrector adapters may be required.
| Flat61a spacing | 67.7 mm backfocus; 12.9 mm adjustment |
|---|---|
| Flat61r spacing | 56 mm backfocus; 1 mm adjustment |
Data sheet
William Optics ZenithStar ZS61 II OTA — 61 mm doublet apochromat This refractor provides a 360 mm focal length at f/5.9. The manufacturer lists a 45 mm image circle and optional correctors for photographic use.
Manufacturer model: William Optics ZenithStar ZS61 II OTA · Specifications checked against manufacturer data on 2026-11-03
