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
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.
Focusing and camera connection
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.
Field correction
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.
Size and weight
Tube length is 245–315 mm and OTA weight is 2.2 kg.
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.
Compatibility notes
Prime-lens telescope: corrector compatibility and spacing are model-specific.
Additional specifications
Flat61a spacing
67.7 mm backfocus; 12.9 mm adjustment
Flat61r spacing
56 mm backfocus; 1 mm adjustment
67480
Data sheet
Aperture (mm)
61
Camera adapters
M54 to 2-inch visual back; 2-inch to 1.25-inch visual back
Camera format
Full frame, APS-C and Micro Four Thirds
Ed glass
Ohara FPL-53
Focal length (mm)
360
Focal ratio
5.9
Focuser travel (mm)
75
Focuser type
2-inch rack and pinion
Image circle (mm)
45
Manufacturer listed correctors
Flat61A 1.0x; Flat61R 0.8x
Mounting plate
Vixen / Arca-Swiss dual-sided
Optical design
Doublet apochromat
OTA weight (kg)
2.2
Tube length (mm)
245–315
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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
