William Optics ZenithStar 81mm ED APO Refractor

The ZS81 is an F/6.9 FPL53 Doublet air-spaced APO with a CNC machined ultra-high precision lens cell, F/5.5 with an optional x0.8-Flattener. It comes wit a 2.5”R&P Ultra robust focuser with 1:10 dual speed: a treat to use during astrophotography. No image shifting! Heavy duty: perfect for your accessories.

It comes with an innovative Bahtinov Mask Cover!

Despite its 81mm objective, the scope is still very compact and solid. Many airlines will accept it as carry-on luggage! Perfect size for serious observations of deep sky objects and planets. Solar observations possible with proper additional equipment.

This beautiful scope is everything you always wanted in a refractor, starting from extreme sharpness for clear details, and APO color correction.

ZenithStar 81 Doublet Apochromatic Refractor

The William Optics ZenithStar 81 is an extremely well crafted and versatile refractor, an ideal instrument for deep sky imaging with DSLRs or dedicated astronomy cameras with APS-C and full-frame sensors. It’s also a great tool for visual observation of a wide range of celestial objects from the moon and planets to nebulae and star clusters and brighter galaxies, as well as for solar observation with a safe solar filter.

The ZS81 features an 81mm f/6.9 FPL 53 air-spaced doublet apochromatic objective lens in a CNC machined ultra-high precision cell. These premium optics provide razor-sharp images and excellent color rendition. When paired with a 0.8x William Optics field flattener and focal reducer (sold separately), the scope works at a fast f/5.5 with a flat field across the entire 43.3mm diagonal of a full-frame sensor.

Premium Build Quality and Compact Form Factor

Like all telescopes from William Optics, the ZenithStar 81 incorporates rock-solid mechanics and built quality. The scope includes high-quality mounting rings to safely and securely hold the telescope to the mount. The rings are anodized to match the color of the handle, dovetail, and focuser, giving the scope an attractive, premium appearance.

With a focal length of 559mm, this f/6.9 telescope has a retracted length of just 456mm (18”), compact enough to qualify as carry-on luggage with many airlines. The tube weighs just 3.50kg (7.8 lbs) including tube rings and dovetail plate.

Heavy-Duty Focuser, Rings, Soft Case and Accessories

The William Optics ZS 81 features a patented objective lens cover that doubles as clear Bahtinov focusing mask. This makes it a snap to achieve sharp focus when setting up for astrophotography.
The ZS 81 also features a heavy duty 10:1 dual-speed 2.5” rack and pinion focuser with tension screws to securely hold a bigger camera and accessories without slipping or image shift, even during longer exposures. The focuser also includes two additional screws to mount an optional red-dot finder.
A convenient CNC-machined carrying handle mounts on top of the rings and doubles as a holder for a guide scope (sold separately). On the bottom of the rings is a 210mm long reversible dovetail with a Vixen rail on one side and an Arca Swiss mount on the other for mounting the scope to a camera tripod for grab-and-go terrestrial and astronomical observation.
A soft carry case is now also included with this telescope.

Flattener (2019 All New Adjustable Flat6AIII [ Buy Separately ])

This very elegant 2″ reducer/field flattener has been designed to optimize the flat-field imaging performance of William Optics F/6 to F7.5 ratio refactors. WO Flat 6AIII will provide good illumination and flat field across 97% of full frame sized sensors.

Full frame size

Designed with nearly Full frame chip-size DSLR cameras in mind.

FMC tripllet APO design.

Produced entirely with the best Ohara optical glasses.

Amazing

Reducing factor 0.8X.

Adjustable design, for perfect back focus it can be used with other models of refractor

48mm filter ready

Superb Finish

William Optics polished anodized finish.

All internal surfaces threaded and blackened to prevent reflections.

Easy to Use

Will accept any standard 48mm wide T-ring for your camera. Not compatible with smaller 42mm T rings.

Premium 73mm apochromatic refractor for astronomical and terrestrial imaging and visual observation

Apochromatic f/6.9 doublet objective with FPL-53 glass

Large image circle for imaging with APS-C and full-frame sensors

Compact form factor and light weight ideal for transport and travel

Includes patented clear Bahtinov mask cover, dual-speed 2.5” focuser, mounting rings, soft carry case, dovetail rail, all color matched for an attractive appearance.

Ohara FPL-53 vs FPL-51 ED Glass

The dispersion properties of ED and SD glass elements are important in determining the overall colour correction. The abbe index is used to quantify the ‘partial dispersion’ of a particular glass. Pure Fluorite offers the highest partial dispersion at around 94.99 V, Ohara FPL-53 glass is very close to Fluorite at 94.93 V and is often referred to as Synthetic Fluorite.  FPL-53 is also noticeably better than Ohara’s lower spec’ FPL-51 glass which offers an abbe index of 81.54 V.

Heavy-Duty Focuser, Rings, Soft Case and Accessories

The William Optics Z81 features a patented objective lens cover that doubles as clear Bahtinov focusing mask. This makes it a snap to achieve sharp focus when setting up for astrophotography.

The Z81 also features a heavy duty 10:1 dual-speed 2.5” rack and pinion focuser with tension screws to securely hold camera and accessories without slipping or image shift, even during longer exposures. One focuser knob even includes an integrated thermometer to help you track small temperature changes that might affect focus during your imaging sessions.

A convenient CNC-machined carrying handle mounts on top of the dual mounting rings. A dovetail in the handle accommodates an additional set of rings for a guide scope (guide scope rings and guide scope sold separately). On the bottom of the mounting rings is a reversible dovetail with a Vixen rail on one side and an Arca Swiss mount on the other for mounting the scope to a camera tripod for grab-and-go terrestrial and astronomical observation.

A soft carry case is now also included with this telescope.

Deep Sky Imaging with the Zenithstar 81 APO

If you are new to deep sky astrophotography but have dabbled in tracked night sky shots including the Milky Way – this is likely the best possible next step for you.

An Affordable Imaging Refractor

The William Optics Zenithstar 81 currently retails for Rupees 93000.00.  The price includes the Telescope, Guiding Scope, Field Flatenner, Guiding Rings, Mounting Rings, Handle Bar, Dovetail Plate, Bahtinov and a Carry Case.

This includes everything from a color-matched dovetail plate to the photo adapter for your DSLR camera.

Ultra-Portable Telescope

It is often said, that the best telescope is the one you use most often. With a retracted length of 330mm and convenient mounting options, you’ll have no excuse not to deploy the Z73 for a night of deep-sky astrophotography on a moment’s notice.

Impressive Features

The built-in star-spikes Bahtinov mask makes focusing your DSLR camera through the telescope quick and easy. Simply point the telescope at a bright star, and position the central spike evenly between the “X”.

The telescope is held securely inside the mounting rings and can be adjusted back and forth to improve balance if necessary.

TECHNICAL DATA
Optical system	Air-spaced doublets with 1 FPL-53 fluorite element
Aperture	81 mm
Focal length	560 mm
Focal ratio	f/6.9
Image circle	Full frame corrected field with Flat6AIII [ Buy Flattener Separately ]
Resolution	1.83 arcseconds
Limiting magnitude	12.9
Camera Format	APS-C, Full Frame
Tube material	Aluminium
Tube construction	Full tube
Focuser	Dual Speed Rack and Pinion
Gear reduction	1:10 Fine movement
Tube clamps	Yes
Dew Shield	Yes
Carrying handle	Yes
Series	ZenithStar
OTA length	460 mm (fully retracted) 560 mm (fully extended)
Recommended For	Advance Users
Weight	3.53 kg
Interchangeable T-Mount	Canon EF, Nikon F, Sony E, Pentax, Micor Four Thirds, Fuji FX