Explore Scientific 82° 11mm Waterproof Eyepiece - 1.25"

The Explore Scientific 82° 11mm Eyepiece: An Immersive 279g Optic

The 11mm is a popular focal length in the upper-medium power class, for any application where more power is desired: globular star clusters, planetary nebulae, the bright cloud structure near the nucleus of comets, and initial observations of planets.

Explore Scientific assembles each eyepiece into precision machined metal lens barrels that maintain the alignment of the optical train for years of rugged use in the field.

The 82° Apparent Field: A Spacewalk Experience

The defining feature of this eyepiece is its 82° apparent field of view. This ultra-wide perspective creates a "spacewalk" effect, where the edge of the field is so far from the center that it effectively disappears from your awareness. The view feels less like looking *through* an instrument and more like being immersed in the scene itself.

This immersive quality naturally promotes relaxation at the eyepiece, allowing you to observe for longer periods without eye strain. Explore Scientific adds that a wide field makes it easy to use averted vision, looking slightly to the side of a faint object so its light falls on a more sensitive part of your eye.

21.6mm Eye Relief: Uncompromised Comfort for All Observers

The 11mm has 21.6mm of eye relief, the distance from the eye lens to where your eye sees the full field. A longer distance means you don't have to press your eye right up against the lens, reducing fatigue and making the experience more comfortable.

Long eye relief helps observers who keep their glasses on, for example to correct astigmatism. Whether you see the whole field with glasses depends on your glasses and eye position.

Optical Design: 7 Elements and EMD Coatings for a High-Contrast Field

The 11mm uses 7 lens elements in 4 groups. Advanced computer design and combinations of low dispersion and high refractive index glasses optimize the 82° Series for high contrast, high resolution and superior flat field characteristics.

• Enhanced Multilayer Deposition (EMD) Coatings: The EMD coatings are durable and the optics fully multi-coated.
• Blackened Lens Edges: The lens edges are blackened to minimize the scattering of light within the lenses.
• Flat Black Interior: All internal surfaces of the barrel are flat black to keep internal reflections to a minimum.

Built for the Field: 100% Waterproof, Argon-Purged Construction

Each 82° Series eyepiece is O-ring sealed and purged with an inert gas (argon) to create a waterproof environment, with a waterproof, fog-proof housing.

Sealing keeps moisture out of the inside of the eyepiece, so the internal surfaces do not fog. Dew can still form on the outer lens.

The 1.25" Barrel: Secure Fit and Universal Compatibility

The Explore Scientific 82° 11mm eyepiece features a standard 1.25" barrel, which fits 1.25" focusers, diagonals and Barlow lenses. The body is 87mm long and 48mm wide.

At 279 g, it is more substantial than a simple Plössl; depending on your setup, you may need to make a small adjustment to your telescope's balance when switching from a much lighter eyepiece.

The 15.9mm Field Stop: Calculating Your True Field of View

The field stop is the physical ring inside the eyepiece that defines the edge of the field of view. In the 11mm 82° eyepiece, this stop has a diameter of 15.9mm. This dimension, combined with your telescope's focal length, lets you work out the true field of view (TFoV), the actual patch of sky you will see.

To calculate the TFoV in degrees, use the following formula:
TFoV ≈ (Field Stop Diameter / Telescope Focal Length) × 57.3

For example, on a telescope with a 1200mm focal length, the true field of view with this eyepiece would be approximately (15.9 / 1200) × 57.3 ≈ 0.76 degrees. That frames the full Moon, about 0.5 degrees across, with room around it.

The 11mm Focal Length: Calculating Magnification for Your Telescope

Magnification is determined by the ratio of your telescope's focal length to your eyepiece's focal length. With its 11mm focal length, this eyepiece will produce medium-high power on most telescopes, perfect for detailed observations.

To calculate the magnification, use this simple formula:
Magnification = Telescope Focal Length / 11mm

• With a 750mm focal length refractor: 750mm / 11mm = 68x magnification.
• With a 1200mm focal length Dobsonian: 1200mm / 11mm = 109x magnification.
• With a 2000mm focal length telescope: 2000mm / 11mm = 182x magnification.

Ideal Targets for an 11mm, 82° Eyepiece

The combination of medium-high power and a wide field makes the 11mm focal length extremely versatile. It has enough power for detail and a wide enough field to keep objects in view longer on non-driven mounts. Suggested targets include:

• Globular Star Clusters: Bright globulars such as the Hercules Cluster (M13) and M92 begin to resolve at this power in a medium or large telescope.
• Planetary Nebulae: Compact objects such as the Ring Nebula (M57) and the Dumbbell Nebula (M27) gain image scale.
• Bright Comet Nuclei: The bright cloud structure near the nucleus of comets.
• Planets: Initial observations of planets, such as Jupiter's cloud bands and moons or the rings of Saturn.

Expanding Magnification with 2x, 3x, & 5x Focal Extenders

Explore Scientific's Focal Extenders give 2X, 3X or 5X magnification increases while maintaining the eyepiece's native apparent field and eye relief. The 1.25" models are the FE02-125, FE03-125 and FE05-125.

Adding a focal extender effectively multiplies your eyepiece collection. For example, pairing this 11mm eyepiece with a 2x Focal Extender gives you the equivalent of a 5.5mm eyepiece, doubling your magnification while keeping the eye relief.

Care and Storage

As a precision optical instrument, the Explore Scientific 82° 11mm eyepiece should be handled with care. Keep it capped and stored when not in use. The sealed body keeps moisture out of the interior, but the outer lens surfaces still need care.

If the outer lenses require cleaning, first remove any loose dust with a blower bulb. Then, use a lens-safe cleaning fluid and a microfiber cloth to gently wipe the surface. Store the eyepiece in a protective case when not in use.

82° Immersion vs. 52° Porthole: The Wide-Field Advantage

Compared to a traditional Plössl eyepiece with a 50°-52° apparent field, the 82° field of this eyepiece offers a fundamentally different observing experience. A standard eyepiece presents a sharp but constrained "porthole" view, where the edge of the field is always apparent. You are always aware you are looking through an instrument.

The 82° design removes this boundary. The view is so expansive that an object can drift for a significant time before exiting the field, requiring fewer adjustments at the telescope. This is particularly beneficial for observers using Dobsonian or other non-motorized mounts.