Explore Scientific 100° 20mm Waterproof Eyepiece - 2"

In a typical 8-inch or 11-inch f/10 Schmidt-Cassegrain Telescope, a 20mm focal length provides medium-to-low magnification (around 100x-140x). This is ideal for framing the entirety of large globular clusters like the Hercules Cluster (M13) or Omega Centauri within the immersive 100° field, showing the cluster against a dark, expansive background.

The primary benefit is context. Large emission nebulae often span several degrees of the sky. The ultra-wide 100° field of the Explore Scientific 20mm eyepiece allows you to see these objects in their entirety, especially when paired with a rich-field refractor. You can trace the full "coastline" of NGC 7000 or the sprawling arms of the Orion Nebula (M42) in a single view.

Argon gas molecules are larger than nitrogen molecules, making them less prone to escaping through the eyepiece's seals over time. This provides a more stable, long-term waterproof and fog-proof solution, ensuring the internal optics remain pristine for the life of the eyepiece.

Yes, a 2-inch barrel is essential. The physical diameter of a 1.25-inch barrel would act as a restrictive aperture, making it impossible to deliver such a wide, well-illuminated 100° field of view to the observer's eye without significant vignetting (darkening at the edges).

This is a rigorous durability standard. It means the eyepiece's seals are robust enough to prevent any water intrusion even when fully submerged. For an astronomer, this translates to complete protection against heavy dew, high humidity, and accidental splashes or rain, preventing internal fogging or damage.

For some observers, yes. Achieving a comfortable view of the entire 100° field at once can depend on your individual eye placement and whether you wear glasses. It is common with ultra-wide eyepieces to slightly shift your eye position to fully appreciate details at the very edge of the field stop.