Sky-Watcher Emerald 22mm 82° Eyepiece

The Sky-Watcher Emerald 22mm: An 82° Eyepiece for Deep-Sky Exploration

The Emerald 22mm is designed for astronomers seeking expansive, high-contrast views of the night sky. With its 22mm focal length, it provides low magnification, and it suits a range of visual applications, deep-sky exploration, lunar landscapes and planetary viewing, and scanning the Milky Way.

As the lowest-magnification eyepiece in the Emerald series, the 22mm gives the widest true field of the three in a given telescope.

A 7-Element System with Broadband Anti-Reflection Coatings

At the core of the Emerald 22mm is a 7-element optical design. It gives high contrast, wide fields and clarity.

Every lens in the optical train is treated with broadband anti-reflection coatings. They give light transmission, high contrast and minimal internal reflections. Additionally, the lens edges are blackened.

The 82° Apparent Field of View

The 82° apparent field of view (AFOV) defines the viewing experience with the Emerald 22mm. This ultra-wide field gives an expansive, immersive view of the night sky.

This wide field is not just about aesthetics; it has practical benefits for observing. For deep-sky observers, it allows you to see large objects in their entirety, framed by the surrounding star fields. When scanning the sky, the wide field means you can cover more area without moving the telescope.

18mm of Eye Relief for Comfortable Viewing with Glasses

The Sky-Watcher Emerald 22mm eyepiece features a generous 18mm of eye relief. Eye relief is the fixed distance from the eyepiece's top lens to the point where your eye's pupil must be placed to see the entire field of view.

The 18mm eye relief is ideal for spectacle wearers and comfortable for extended sessions, even with glasses. The eyepiece has a soft rubber eyecup.

Calculating Magnification with the 22mm Emerald Eyepiece

The magnification provided by the Emerald 22mm eyepiece depends entirely on the focal length of your telescope. To calculate it, simply divide your telescope's focal length (in millimeters) by the eyepiece's focal length, which is 22mm. For example, in a telescope with a 1200mm focal length, the eyepiece yields approximately 55x magnification (1200 / 22 ≈ 54.5).

The True Field of View (TFOV), or the actual patch of sky you see, can also be estimated. Divide the eyepiece's 82° apparent field by the magnification. Using the same 1200mm telescope at 55x, the true field would be about 1.5° (82 / 55 ≈ 1.49). The full Moon is about 0.5° across, so this field spans about three Moon diameters.

• Short Focal Length Telescope (e.g., 600mm): Provides a very low 27x magnification.
• Medium Focal Length Telescope (e.g., 1200mm): Gives 55x.
• Long Focal Length Telescope (e.g., 2000mm): Yields 91x.

Calculating Exit Pupil: Matching the 22mm to Your Telescope's f-ratio

The exit pupil is the small beam of light that exits the eyepiece and enters your eye. Its diameter is calculated by dividing the eyepiece focal length (22mm) by the telescope's focal ratio (f-number).

In an f/4.7 telescope the 22mm Emerald gives a 4.7mm exit pupil (22 / 4.7); in an f/10 telescope 2.2mm (22 / 10). A fully dilated eye pupil is about 7mm, less with age, so very fast telescopes with long eyepieces can exceed what your eye takes in.

A Standard 2" Barrel with Threads for Filters

The Sky-Watcher Emerald 22mm eyepiece is built with a 2" diameter barrel. It fits telescopes with a 2" focuser or a 2" star diagonal.

The barrel is threaded to accept standard 2" filters. This allows you to easily attach filters to enhance your view without needing a separate filter wheel or slide.

Using the 22mm Emerald with f/4 to f/10 Telescopes

Sky-Watcher does not rate the Emerald eyepieces by telescope focal ratio. In slower telescopes the 22mm gives higher magnification and smaller exit pupils; in faster ones lower magnification, a wider true field and larger exit pupils.

A 600g CNC-Machined All-Metal Body for Field Use

The Emerald 22mm is constructed from a precision CNC-machined all-metal body, built to withstand years of observing in the field. The exterior is finished in high-gloss anodized aluminium.

It weighs 600g (1.3 lb), so check your telescope's balance after swapping to it from a lighter eyepiece. The eyepiece includes a custom-fit carry case with a durable exterior to shield it from bumps, dust, and moisture during transport and storage.

Emerald 22mm vs. 16mm & 9mm: Choosing Your Focal Length

All eyepieces in the Sky-Watcher Emerald series share the same 82° apparent field of view and 7-element optical design. The primary differences are focal length, barrel size, and eye relief, which tailor each eyepiece for different magnifications and targets.

• Emerald 22mm (2"): As the lowest power option, it has the longest eye relief of the three, 18mm, which is ideal for spectacle wearers.
• Emerald 16mm (2"): This eyepiece offers a step up in magnification from the 22mm. It has 14mm of eye relief in a 2" barrel.
• Emerald 9mm (1.25"): Providing the highest magnification in the series, the 9mm has a shorter 8mm eye relief and fits standard 1.25" focusers.

Maintaining Your 7-Element Optics: Care and Cleaning

There are no specific cleaning instructions for the Emerald eyepieces. Store the eyepiece in its carry case between sessions and avoid touching the lens surfaces.