Explore Scientific 92° ED Series 25mm Waterproof Eyepiece

The 92° Apparent Field at 25mm

The 25mm delivers an ultra wide, low magnification view that lets you fully immerse yourself in the night sky, with a dramatic, panoramic perspective that enhances the sense of space. You may even forget there is an eyepiece between you and the universe.

It is ideal for large deep sky objects and sweeping expansive star fields, with large objects viewed in full context.

19.6mm of Eye Relief for Comfortable Extended Viewing

The 25mm has 19.6mm of eye relief. The series' long eye relief serves up great views with reduced eyestrain and comfort during extended sessions.

A 10-Element, 7-Group Design with ED Glass

The 25mm uses 10 elements in 7 groups, including extra-low dispersion (ED) glass. ED glass reduces chromatic aberration, the false color fringing around bright objects, because its high Abbe number spreads white light into colors less.

Explore Scientific credits it with:

• Higher Contrast: Increased contrast and clarity.
• Truer Color Rendition: Colors closer to reality, such as subtle differences in star color.
• Edge-to-Edge Sharpness: The view stays sharp and well defined across the entire field.

Argon-Purged Waterproofing for 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 2-Inch Barrel: Secure Fit and Physical Dimensions

The 92° 25mm uses a 2-inch barrel, tapered for extra security.

With an overall length of 143mm and a maximum outer diameter of 76mm, this is a substantial eyepiece. The catalog gives no weight for the 92° ED Series.

Calculating True Field from the 36.7mm Field Stop

The true field of view (TFoV), the actual patch of sky you see, is determined by the eyepiece's 36.7mm field stop diameter and your telescope's focal length. You can calculate the TFoV for your specific instrument using a simple formula: (Field Stop Diameter / Telescope Focal Length) x 57.3.

For example, in a telescope with a 2000mm focal length, this eyepiece would yield a true field of approximately 1.05°. At 840mm focal length it is about 2.5°, and at 1200mm about 1.75°.

Magnification Examples with a 25mm Focal Length

The 25mm focal length is designed for low-power, wide-field observation. The exact magnification depends on your telescope's focal length (Telescope FL / 25mm = Magnification).

• 2000mm focal length: 80x.
• 1200mm focal length: 48x.
• 714mm focal length: about 29x.

Expanding Magnification with 2-Inch Focal Extenders

Optional focal extenders are available for the series; a focal extender increases the magnification of any eyepiece with the same barrel size.

The following 2-inch models are compatible:

• FE02-020 2x Focal Extender: This transforms the 25mm eyepiece into an effective 12.5mm.
• FE03-020 3x Focal Extender: This provides a 3x magnification boost, giving you an effective 8.3mm focal length.

Care and What Is in the Box

The box holds the eyepiece. Avoid touching the lens surfaces with your fingers.

The sealed housing keeps the inside closed; clean only the outer lenses, and only when needed.