Explore Scientific 68° 40mm Waterproof Eyepiece - 2"

The 40mm, 68° Wide-Field View: Maximum Context in a 2" Barrel

With a 40mm focal length, this eyepiece provides very low magnification, making it an ideal tool for locating objects and framing the largest deep-sky targets. The expansive 68° apparent field of view creates a "spacewalk" experience, allowing you to see large structures like the Andromeda Galaxy (M31) or the North American Nebula (NGC 7000) in their entirety within many long-focal-length telescopes.

Argon-Purged & Waterproof: Sealed for 30 Minutes at 1 Meter

By purging the optical housing with inert argon gas, Explore Scientific prevents the growth of internal fungus and eliminates fogging during nights with heavy dew. Unlike nitrogen, the larger argon atoms are less likely to leak through seals over time, ensuring the eyepiece remains pristine for years. This sealed environment means you can clean the eyepiece without risk of solvents seeping between lens elements, a critical feature for maintaining optical contrast.

• Tested Immersion: Every eyepiece is tested to be waterproof for 30 minutes in one meter of water, guaranteeing performance in any observing condition.
• Inert Environment: The argon-purged interior protects delicate multi-coatings from degradation caused by moisture and contaminants.
• Thermal Stability: Argon's lower thermal conductivity helps buffer the optics against rapid temperature drops, reducing the risk of thermal shock.

Parfocal Design & Long Eye Relief: A Focus on Observer Comfort

This eyepiece features long eye relief and a soft, foldable silicone eyecup, making it comfortable for all observers, including those who wear eyeglasses. It is also parfocal with other eyepieces in the Explore Scientific 68° series, meaning you can switch between different magnifications with little to no refocusing required. This convenience saves valuable time at the telescope, keeping your target sharp as you change your view.

Explore Scientific 40mm 68° vs. TeleVue 55mm Plössl: Apparent vs. True Field

When choosing a low-power 2" eyepiece, it's critical to understand the trade-offs between apparent field of view (AFOV) and true field of view (TFOV).

• TeleVue 55mm Plössl's Advantage: The 55mm Plössl is designed to produce the widest possible TFOV in a 2" barrel. It's the ultimate "finder" eyepiece, showing the largest possible patch of sky at the lowest magnification, but with a narrower 50° AFOV.
• Explore Scientific 40mm's Advantage: The ES 40mm prioritizes an immersive viewing experience with its wide 68° AFOV. While its TFOV is slightly smaller than the 55mm Plössl's, the "picture window" effect is much more pronounced. Additionally, its waterproof construction offers a level of environmental protection the Plössl does not.