Takahashi Starbase OR-20mm Orthoscopic Eyepiece

Product Overview

The Starbase OR-20mm is a 20mm orthoscopic eyepiece from Takahashi's Starbase accessory line, built on the same 4-elements-in-2-groups design as the rest of the OR series, aimed at low distortion toward the center of the field. It has a 45° apparent field of view, 14mm of eye relief, and weighs 82g. Takahashi lists an overall body size of 33mm x 45mm (diameter x length) for this specific model.

Who It's For

This is a good match if you want a low-power orthoscopic view — wider star fields, lunar overviews, and framing shots before switching to a shorter focal length for detail, with the sharper center-field correction orthoscopic designs are built for.

Key Features & Design

• Orthoscopic 4-element, 2-group design: low distortion, particularly at the center of the field.
• 45° apparent field of view: a comfortably wide window at this focal length.
• 14mm eye relief: comfortable for eyeglass wearers.
• 82g weight: light enough to leave a small refractor's balance unaffected.

Optical / Mechanical Design

The four-element, two-group orthoscopic layout is chosen for correction rather than field width — it holds sharpness and low distortion from the center out, which is the trait orthoscopic eyepieces have historically been valued for on the Moon and planets. At 20mm, the OR-20mm sits at the low-power end of the Starbase orthoscopic range, useful as a wide-view complement to the shorter focal lengths in the same series.

Recommended Uses

On a Takahashi FS-60CB (355mm, f/5.9) the OR-20mm gives about 18x, a wide, bright view for star fields and open clusters. On a TSA-120 (900mm, f/7.5) the same eyepiece yields roughly 45x — a comfortable low-power view of the Moon and larger deep-sky targets. Divide any Takahashi tube's focal length by 20mm for the magnification on your own setup.

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 a standard 1.25” focuser or diagonal.

What is it best used for?

Low-power visual observing — wide star fields and lunar overviews, with the low-distortion correction of an orthoscopic design.

How does it differ from the OR-18mm?

Both use the same 4-element orthoscopic layout; the OR-20mm's slightly longer focal length gives a touch lower magnification and a marginally larger exit pupil on the same telescope.

What telescopes does it fit?

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

Bottom Line

A 20mm orthoscopic eyepiece with a 45° field, 14mm eye relief, and an 82g weight — a wide, low-power view built around the same distortion-controlled optics as the rest of the Starbase OR series. If you're building 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.