William Optics AP 81/559 ZenithStar 81 Red OTA Apochromatic refractor

The William Optics ZenithStar line offers compact yet high-quality apochromatic refractors, perfect for DSLR camera use. These scopes excel at capturing wide-angle images of expansive star fields. When paired with an optional flattener, they deliver corrected imagery across a 45-millimeter diameter, right to the edges.

The lightweight and compact ZenithStar apochromats, alongside a DSLR, integrate seamlessly onto photography mounts like the Skywatcher Star Adventurer or iOptron Star Tracker, creating a simple, portable astrophotography system.

The ZS81 is an F/6.9 FPL53 Doublet air-spaced APO featuring a CNC machined ultra-high precision lens cell. With an optional x0.8 flattener, it operates at F/5.5. Equipped with a robust 2.5” R&P focuser with 1:10 dual speed, it ensures smooth operation during astrophotography without any image shifting. Heavy-duty construction makes it ideal for accommodating accessories.

This model also includes an innovative Bahtinov Mask Cover!

Despite its 81mm objective, the scope remains compact and sturdy, often accepted as carry-on luggage by many airlines. Its size is perfect for serious observations of deep sky objects and planets, with the potential for solar observations with additional equipment.

This exquisite scope fulfills all your refractor desires, boasting extreme sharpness for clear details and APO color correction.

Included accessories

• Carrying handle: Yes
• Carry case: Yes
• Miscellaneous: Bahtinov focus mask
• Tube clamps: Yes
• Prism rail: Arca-Swiss & Vixen-Style
• Dew Shield: Yes

SPECIFICATIONS

Optics

Type: Refractor

Aperture (mm): 81

Focal length (mm): 559

Aperture ratio (f/): 6.9

Resolving capacity: 1.70

Limit value (mag): 11.3

Light gathering capacity: 130

Max. useful magnification: 162

Carrying length (mm): 456

Tube weight (kg): 3.5

Lens design: Doublet

Type of build: Apochromat

Focuser

Type of build: Gear rack

Connection (to eyepiece): 2

Gear reduction: 1:10 Fine movement

Connecting threaded socket (camera-side): M63

Free aperture (mm): 64

Mount

Type of build: OTA

Mounting type: No mount

General

Series: ZenithStar

Colour: Red

Area of application

Astrophotography: Yes (very good)

Moon & Planets: Yes (very good)

Nature Observation: No

Nebulae & galaxies: Yes

Sun: No (Only with appropriate Sun filter)

Recommended for

Beginners: No

Advanced: Yes

Observatories: No