Explore Scientific 68° 28mm Waterproof Eyepiece - 2"

A 68° Flat-Field Window on the Sky

Using a combination of low-dispersion and high-refractive-index glasses, this 28mm eyepiece is optimized for high contrast and resolution across its entire 68° apparent field. The result is a superior flat field, keeping stars sharp from the center to the edge, a critical feature when observing dense open clusters or extended nebulae.

The multi-layer coatings on all air-to-glass surfaces maximize light transmission, ensuring that the faintest stars and subtle details in galaxies are not lost. This optical design makes the eyepiece a versatile workhorse for everything from sweeping the Milky Way to framing large targets like the Andromeda Galaxy (M31).

Argon-Purged for a Lifetime of Clarity

Explore Scientific seals this eyepiece and purges the internal volume with inert argon gas, making it completely waterproof and internally fog-proof. To ensure this seal, every eyepiece is tested by submerging it in one meter of water for 30 minutes. This process prevents the growth of internal fungus and protects the coatings from contaminants over the lifetime of the eyepiece.

Argon is chosen over nitrogen for its larger atomic size, making it less likely to leak through seals over time. Its superior inertness also prevents chemical reactions with internal components, extending longevity and ensuring the optics remain as pristine as the day they were assembled, regardless of dew, humidity, or rapid temperature drops.

Long Eye Relief and Parfocal Convenience

This eyepiece features long eye relief, providing comfortable views for all observers, including those who wear glasses. A soft, foldable silicone rubber eyecup allows you to set the perfect eye distance to see the full field of view while blocking stray light, which is critical for detecting faint details at the limit of vision.

As part of an integrated eyepiece series, the 68° 28mm is designed to be nearly parfocal with other eyepieces in the line. This minimizes the amount of refocusing needed when switching between different focal lengths, saving valuable observing time and making comparisons between views much more efficient.

ES 68° 28mm vs. the 82° Series: Field of View and Eye Placement

While the Explore Scientific 82° series offers a more expansive "spacewalk" effect, the 68° series presents a different set of advantages. The primary trade-off is the apparent field of view against eye comfort and optical tolerance.

• Explore Scientific 82° Series Advantage: The wider 82° field provides a more immersive sensation and can fit slightly larger objects into the view at a similar magnification. It is often the choice for observers prioritizing the widest possible apparent field.
• Explore Scientific 68° 28mm Advantage: The 68° field is significantly less demanding on telescope optics, showing better edge-of-field performance in fast Newtonians. It also typically features more comfortable eye relief, making it easier to hold the full field of view, especially for eyeglass wearers or those new to wide-field eyepieces.