Explore Scientific 92° ED Series 20mm Waterproof Eyepiece

92° Apparent Field at 20mm: A Panoramic Deep-Sky Window

The 92° field creates a panoramic experience that enhances the sense of depth and scale, and objects remain in view longer, making observation more fluid. You may even forget there is an eyepiece between you and the universe.

The 20mm strikes a balance of brightness and magnification, particularly effective for deep sky objects, for observers who want a wide field while keeping enough magnification to reveal structure and detail.

9-Element Design with ED Glass

The optics include extra-low dispersion (ED) glass. ED glass has a high Abbe number, so it spreads white light into colors less, and it offers reduced color fringing, sharper high-contrast views and better performance at high magnification.

The 9-element, 6-group design is fully multi-coated and edge-blackened for maximum contrast. In the 20mm, color fringing is minimized and contrast enhanced, for a clean, detailed image.

20.2mm of Eye Relief

Designed for long nights at the telescope, the eyepiece features a generous 20.2mm of eye relief. This is the distance from the top lens of the eyepiece to the point where your eye must be placed to see the entire field of view. The series' long eye relief serves up great views with reduced eyestrain and supports extended observation.

Argon-Purged Waterproofing: All-Weather Reliability

Each eyepiece is O-ring sealed and purged with an inert gas to create a waterproof environment, with a waterproof, fog-proof housing.

The 31.7mm Field Stop: Calculating Your True Field of View

The field stop is the physical aperture inside the eyepiece that defines the edge of the field of view. In the 20mm 92° eyepiece, this is a large 31.7mm. This dimension, not the apparent field, is what determines the actual patch of sky you will see, known as the True Field of View (TFoV). You can calculate the TFoV for your specific telescope with a simple formula.

To find your TFoV in degrees, divide the eyepiece's field stop diameter (31.7mm) by your telescope's focal length in millimeters, and then multiply the result by 57.3.
Formula: TFoV ≈ (31.7mm / Telescope Focal Length in mm) × 57.3
For example, in a telescope with a 1500mm focal length, the true field would be approximately 1.2 degrees (about 1.5° at 1200mm and 0.9° at 2000mm).

The 20mm Focal Length: Calculating Magnification Examples

An eyepiece's magnification is determined by the focal length of the telescope it is used in. To calculate the magnification, simply divide your telescope's focal length by the eyepiece's focal length (20mm).

• 600mm focal length: 600 / 20 = 30x.
• 1200mm focal length: 1200 / 20 = 60x.
• 2800mm focal length: 2800 / 20 = 140x.

2x & 3x Magnification: Using Optional 2-Inch Focal Extenders

You can increase the versatility of the 20mm 92° eyepiece by pairing it with an Explore Scientific Focal Extender. Optional focal extenders are available for the series, and a focal extender increases the magnification of any eyepiece with the same barrel size.

Because this eyepiece uses a 2-inch barrel, it is compatible with Explore Scientific's 2-inch focal extenders. Using one of these accessories essentially gives you additional eyepieces in your case.

• With a 2x Focal Extender (FE02-020): The eyepiece effectively performs like a 10mm eyepiece, doubling its magnification.
• With a 3x Focal Extender (FE03-020): The eyepiece provides the magnification of a 6.7mm eyepiece.

The 164mm, 2-Inch Tapered Barrel: Secure Fit and Finish

The Explore Scientific 92° 20mm eyepiece is a substantial ocular, measuring 164mm in length with a maximum outer diameter of 77mm. The catalog gives no weight for the 92° ED Series.

The barrel is tapered for extra security, with durable coating and finishing touches.