Takahashi Starbase OR-18mm Orthoscopic Eyepiece

Product Overview

The Starbase OR-18mm is an 18mm orthoscopic eyepiece from Takahashi's Starbase accessory line, built on a 4-elements-in-2-groups design that keeps distortion low, particularly toward the center of the field. It has a 45° apparent field of view, 13mm of eye relief, and a 1.25” (31.7mm) barrel that fits standard Takahashi focusers and diagonals. Optical coatings are fully multi-coated throughout.

Who It's For

This is a good match if you want a sharp, low-distortion eyepiece at a moderate focal length — for lunar terrain, double stars, and planetary detail on nights when a mid-power view suits the seeing better than the highest-power eyepiece in your case.

Key Features & Design

• Orthoscopic 4-element, 2-group design: favors low distortion and center sharpness over the widest possible field.
• 45° apparent field of view: a moderate window that keeps the target centered without much drifting during unguided visual sessions.
• 13mm eye relief: workable for observers who wear glasses.
• Fully multi-coated optics: reduces internal reflections and improves contrast.
• 1.25” (31.7mm) barrel: the Takahashi standard, fits existing focusers and diagonals without an adapter.

Optical / Mechanical Design

Orthoscopic eyepieces trade field width for correction at the center of the view — the four-element, two-group layout used here is chosen specifically to hold that correction with low distortion, which is why orthoscopics remain a common choice for high-contrast planetary and lunar observing even though wider-field designs have become more common elsewhere in the eyepiece market. At 18mm, the OR-18mm sits toward the low-power end of the Starbase orthoscopic range.

Recommended Uses

On a Takahashi FS-60CB (355mm, f/5.9) the OR-18mm gives about 20x, a comfortable low-power view for star fields and lunar overviews. On a TSA-120 (900mm, f/7.5) the same eyepiece yields roughly 50x — a solid all-purpose magnification for the Moon, brighter planets, and double stars. Divide any Takahashi tube's focal length by 18mm for the magnification on your own setup.

Compatibility and Accessory Notes

The 1.25” (31.7mm) barrel fits any Takahashi focuser, star diagonal, or 2″-to-1.25” adapter already in the current lineup, so it slots into an existing eyepiece case without any extra hardware.

Good to Know Before You Order

Not parfocal: Takahashi lists this eyepiece as non-parfocal, so a small refocus is needed when you switch to it from another eyepiece.

Frequently Asked Questions

Is it difficult to set up?

No — it threads directly into a 1.25” focuser or diagonal.

What is it best used for?

Moderate-power visual observing — lunar detail, double stars, and planets, with the low-distortion correction orthoscopic designs are known for.

How does it differ from the Starbase KE eyepieces?

The KE (Kellner) eyepieces use a simpler 3-element design and lean toward wider, lower-power views; the OR (orthoscopic) eyepieces use a 4-element design tuned for sharper, more distortion-free images at the center of the field.

What telescopes does it fit?

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

Bottom Line

An 18mm orthoscopic eyepiece with a 45° field, 13mm eye relief, and the standard 1.25” barrel — a sharp, moderate-power choice for lunar and planetary detail. If you're putting together 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.