Explore Scientific 52° 40mm Waterproof Eyepiece - 2"

Deep-Sky Views: The 40mm Focal Length Advantage

With a 40mm focal length, this eyepiece is engineered for observers hunting the faintest objects at the limit of their telescope's reach. The low magnification darkens the sky background and increases surface brightness, making it ideal for framing large targets like the Andromeda Galaxy (M31), the Rosette Nebula (NGC 2244), and sprawling open star clusters.

A 52° Flat-Field Window on the Sky

The Explore Scientific 52° 40mm uses a flat-field optical design with 4 elements in 2 groups. This corrects for field curvature, keeping stars sharp across the entire 52° apparent field. The high-contrast optics make it easier to use averted vision—looking slightly to the side of a faint object—to detect subtle details in galactic structure or faint nebulosity that would otherwise be invisible.

Built for the Field: Argon-Purged and Waterproof in a 2" Barrel

Designed for real-world observing conditions, this eyepiece is fully waterproof and purged with inert argon gas. This process prevents internal fogging during nights with heavy dew and stops contaminants like dust or fungus from ever entering the sealed optical path. As the only 2-inch model in the 52° lineup, it's built to provide a lifetime of reliable views.

Choosing Your 40mm: 52° vs. 62° and 68° Series Eyepieces

Explore Scientific offers three distinct 40mm eyepieces, each serving a different purpose. The choice depends on your priority between an immersive field and maximum viewing comfort.

• 52° Series (This Model): Offers 27.1mm of eye relief, the longest in the 52° Series. It's the top choice for observers who wear glasses or prefer the most comfortable, relaxed view without needing to press their eye close to the lens.
• 62° and 68° Series: These eyepieces provide a significantly wider, more immersive apparent field of view. They also offer longer eye relief (28.2mm and 31mm), so eyeglass wearers can use them too.