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William Optics 1.25" Swan Series Eyepiece - 20mm

William Optics 1.25" Swan Series Eyepiece - 20mm

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The Swan eyepieces are super wide angle designs with a 72° apparent field of view. They use simple but sophisticated five-lens optical systems for generally higher contrast than the more complicated optical designs used in some other super wide angle eyepieces that use up to eight lenses. All lenses are fully multicoated for high light transmission. Lens edges and internal field stops are blackened to reduce internal reflections and improve contrast. The eyepiece rubber grip ring is useful for safer handling of the eyepieces in cold weather when wearing gloves. The eyepieces have soft roll down rubber eyecups for eyeglass use. They can be used for all types of observing, with all telescope types, but they are recommended for use with focal ratios up to f/6 and above. Dust caps are provided for both ends of each eyepiece. A soft protective drawstring-equipped velvet storage bag is standard equipment with each.

This 5-element super-wide angle 1.25" 20mm SWAN EP's panoramic views at 72 deg. FOV will leave you speechless!  A premium eyepiece at a fraction of the cost its worth!

Super Wide FOV
Outstanding super-wide field of view: 72 deg. FOV
Fully Multicoated lenses for excellent transmittance.
Reduced chromatic aberration.
Improved contrast compared to similar EPs.

Great Contrast
Internally fully blackened (lens edges and internal spacers).
No flaring or ghosting on high-contrast objects.

Light and Easy
Soft rubber eyecup.
Long eye-relief: 17mm.
No internal reflections, kidney beaning or other distracting distortions.

Terrific Fit and Finish
High-resistance anodized black barrel.
Smooth design for no hook up in your focuser.
Threaded for use with 1.25" filters.

Eyepiece Series

SWAN Series

Focal Length


Barrel Size

1.25" (31.7mm)

Apparent Field of View (Mfg Specified)


Filter Threads

Standard 1.25" Filter Thread (M28.5 x 0.6)

Eye Relief


Fully Multi-Coated

Lens Elements


Lens Groups

Blackend Lens Edges

Barrel Type
Tapered barrel

Height (With Eyeguard Extended)

Rubber Eye Guard


100 g

Note: Occasionally, the product you receive might have a slightly different cosmetic appearance or labeling than what is shown. This can often change from batch to batch according to the whims of the manufacturer. However, you will always receive a brand new, original product as described above.

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Filed under: Eyepieces & Accessories