William Optics Zenithstar 81 81/559 f / 6.9 in white and red, with a dedicated FLAT 6A III field flatness corrector (WO P-FLAT6AIII).
William Optics Zenithstar 81 is one of the most recognizable structures on the market, intended for both astrophotography and visual observation.
The achievement of extremely sharp images with perfectly corrected chromatic aberration is due to the advanced and precisely made optics. The construction of this refractor is a low-dispersion doublet with an air gap, in which the ED element is made of FPL-53 glass (synthetic fluorite). This material, produced by the Japanese company Ohara, has an extremely high Abbe number (94.94), and is additionally much more chemically stable and easier to process than crystalline fluorite. The surfaces of the lenses have been additionally covered with an SMC coating, the role of which is to improve the contrast by eliminating possible light reflections. The combination of all these features means that, despite its two-element structure, the telescope is often described as a full-fledged apochromat.
The set with the optical tube includes a professional focal length reducer and FLAT 6A III flattener. It is a triplet made of the best optical glasses by Ohara, which allows for cooperation with both full-frame matrices as well as the APS-C and M4 / 3 formats.
The tube of the telescope is mounted on precisely made clamps, equipped with a Vixen socket for the mounting of a finder or guider, as well as a Vixen / Arca-Swiss foot.
• a doublet with an air gap and a low-dispersion element made of Japanese FPL-53 glass (synthetic fluorite)
• three-element focal length reducer / flattener with a multiplicity of 0.8x with the possibility of mounting filters mounted in a holder with an M48 thread
• solid rack & pinion extractor equipped with coarse and fine focus adjustment knobs
• optical tube clamps made in CNC technology
• mounting foot compatible with Vixen and Arca-Swiss sockets, allowing the tube to be mounted on a mount or photographic tripod
• optical system of the telescope: ED doublet with air gap
• flattener / focal reducer: FLAT 6A III
• flattener / focal reducer optics: apochromatic triplet with full multilayer coating (FMC)
• multiplicity of the flattener / focal reducer: 0.8x
• Objective diameter: 81 mm
• focal length (without FLAT 6A III): 559 mm
• focal length (with FLAT 6A III): 447 mm
• lighted up (without FLAT 6A III): f / 6.9
• lighted (from FLAT 6A III): f / 5.5
• maximum usable magnification: 162x
• ED lens material: FPL-53 glass (Ohara, Japan)
• optical system coating: SMC coating
• Compatible sensor sizes: APS-C, full frame
• compatible photographic systems (via interchangeable T-rings): Canon EF, Nikon F, Sony E, Pentax, Micro 4/3, Fuji FX
• back focus (for FLAT 6A III): 60.2 mm
• correction (for FLAT 6A III): 5.2 mm
• fokuser: 2.5 "
• type of eyepiece extractor: rack & pinion, dual speed
• thread for connecting the flattener / focal reducer: M63
• finder foot: Vixen
• mounting for mounting: Vixen / Arca-Swiss
• tube length (folded): 460 mm
• tube length (extended): 560 mm
• tube weight: 3.5 kg
• tube finish: white - red
• William Optics Zenithstar 81 refractor (red)
• FLAT 6A III flattener / focal reducer
• the pupa
• Bahtinov's mask with its mount
• a lens cap
• fixing clamps with the Vixen / Arca-Swiss foot