Takahashi Starbase KE-25mm Kellner Eyepiece

Product Overview

The Starbase KE-25mm is a 25mm Kellner eyepiece from Takahashi's Starbase accessory line, built around the same 2-groups, 3-element optical layout as the KE-20mm. It delivers a 45° apparent field of view and 18mm of eye relief, and weighs 77g — the longest focal length, and so the lowest power and widest exit pupil, in the Starbase Kellner pairing.

Who It's For

This is a good match if you want the lowest-power, widest-view eyepiece in your case — for locating targets, scanning the Milky Way, or getting a bright, easy view before moving to a shorter focal length for detail.

Key Features & Design

• Kellner optical design: 2 groups, 3 elements, simple and well-corrected at the center of the field.
• 45° apparent field of view: a wide window at 25mm focal length.
• 18mm eye relief: generous, comfortable for eyeglass wearers.
• 77g weight: matches the KE-20mm, so the pair balances the same way in a focuser.

Optical / Mechanical Design

The Kellner layout — a plano-convex field lens paired with a cemented achromatic eye lens — keeps the design simple while holding correction at the center of the field, which is where a low-power, wide-view eyepiece like this one is used most. At 25mm, this is the longer of the two Starbase Kellner focal lengths, producing the largest exit pupil and lowest magnification in the pairing.

Recommended Uses

On a Takahashi FS-60CB (355mm, f/5.9) the KE-25mm gives about 14x, a very wide, bright view suited to large star fields and the Milky Way. On a TSA-120 (900mm, f/7.5) the same eyepiece yields roughly 36x — useful as a locating eyepiece before switching to higher power. Divide any Takahashi tube's focal length by 25mm for the magnification on your own setup.

Compatibility and Accessory Notes

Most of the Starbase and Takahashi eyepiece lines use the 1.25” (31.7mm) barrel standard, which fits every current Takahashi focuser, star diagonal, and 2″-to-1.25” adapter.

Good to Know Before You Order

Not parfocal with the rest of the range: expect to refocus when you swap eyepieces.

Frequently Asked Questions

Is it difficult to set up?

No — it drops into any 1.25” focuser or diagonal and is ready to use immediately.

What is it best used for?

Low-power, wide-field visual observing — locating targets, scanning star fields, and framing before you switch to a shorter focal length.

How does it compare to the KE-20mm?

Same Kellner design and weight; the KE-25mm's longer focal length gives a lower magnification and larger exit pupil on the same telescope, useful as the wide end of a two-eyepiece kit.

What telescopes does it fit?

Any Takahashi refractor or reflector with a standard 1.25” focuser or diagonal.

Bottom Line

A 25mm Kellner eyepiece with a 45° field and 18mm of eye relief — the widest, lowest-power option in the Starbase Kellner pairing. If you're building out a full eyepiece set and want help matching focal lengths to your telescope, send us your setup and we'll work it out with you.