Takahashi 2" Mirror Diagonal with 1.25" Adapter

Product Overview

The 2″ Mirror Diagonal with 1.25″ Adapter is Takahashi's full-aperture visual diagonal, built to the same 1/10-wave optical standard as the secondary mirrors in its Epsilon astrographs. It accepts a 2″ (50.8 mm) barrel on both the telescope and eyepiece sides, with a 106.5 mm light path, and ships with the 1.25″ Adapter (TKA00111) included so you can run 1.25″ eyepieces through the same diagonal. The diagonal mirror alone weighs 460 g; with the adapter fitted, the complete kit is 505 g.

Who It's For

This is a good match if you observe visually through a Takahashi refractor or Newtonian and want full 2″ aperture through the diagonal rather than the light loss of stepping down to 1.25″ early in the light path.

Key Features & Design

• Full 2″ (50.8 mm) clear aperture: passes the full cone of light from wide-field 2″ eyepieces without the vignetting a 1.25″ diagonal introduces.
• 1/10-wave mirror figure: matched to the optical standard Takahashi uses on its own telescope secondaries.
• Fully blackened interior: controls internal reflections and stray light.
• 1.25″ Adapter included: steps the eyepiece side down to 31.75 mm when you want 1.25″ eyepieces or accessories, at no extra light path cost beyond the adapter's own 11 mm.

Optical / Mechanical Design

A 90-degree mirror diagonal folds the visual light path for a comfortable viewing angle on a telescope pointed high. The mirror substrate carries a 1/10-wave figure and Takahashi's mirror coating, and the housing accepts a 2″ (50.8 mm) barrel on the telescope side plus an M48 x 0.75 female thread, with a 2″ (50.8 mm) female barrel on the eyepiece side. Light path length through the diagonal is 106.5 mm — a figure to include when you're totaling backfocus for a visual train. See the Takahashi Back Focus Guide.

Recommended Uses

Wide-field visual observing with 2″ eyepieces; general-purpose visual diagonal for any Takahashi refractor or Newtonian with a 2″ focuser; stepped down to 1.25″ with the included adapter for higher-power eyepieces or a Barlow.

Compatibility and Accessory Notes

Fits any 2″ (50.8 mm) focuser drawtube or visual back, either directly on the barrel or via the M48 x 0.75 thread. Not compatible with the classic FSQ-106, which uses a different focuser interface. Pairs with the 1.25″ Adapter (included) for 1.25″ eyepieces and accessories; the adapter is also sold separately if you need a spare.

Good to Know Before You Order

It's a visual accessory, not an imaging one. There's no camera-side thread — it's built for eyepieces.

It isn't compatible with the classic FSQ-106. Takahashi notes this directly; if you're not sure which FSQ generation you have, send us your telescope's serial number and we'll confirm the fit.

Frequently Asked Questions

Is it difficult to set up?

No — it drops into any 2″ focuser or visual back and locks with the same thumbscrews as any diagonal.

What is it best used for?

Full-aperture visual observing with 2″ eyepieces, and 1.25″ eyepieces once the included adapter is fitted.

Does it work for astrophotography?

It's a visual diagonal — mirror diagonals fold the light path for eye observing rather than a straight-through imaging train.

What's included?

The 2″ mirror diagonal and the 1.25″ Adapter (TKA00111).

Bottom Line

A full-aperture, 1/10-wave 2″ mirror diagonal that ships with a 1.25″ adapter included, giving you both eyepiece sizes off a single 106.5 mm light path.