Takahashi Photo Tube Extension DT

Product Overview

The Photo Tube Extension DT is Takahashi's Coupling (DT), an M55.9 x 0.75 ring built specifically for the "DT" photo/visual train. Takahashi publishes its light path at 18 mm, and it comes with one notable restriction: it won't thread onto every M55.9 part in the lineup.

Who It's For

This is a good match if your Takahashi system chart calls for the Coupling (DT) specifically, or you're assembling a camera train on the M55.9 accessory standard and need this exact spacing.

Key Features & Design

• M55.9 x 0.75 thread: Takahashi's drawtube-accessory standard shared across several refractors.
• Coupling (DT) — Takahashi part TKP20006B: the manufacturer's own designation.
• 18 mm light path: a mid-length step in the M55.9 family, between the 10 mm Visual Coupling S and the 30 mm Extension Tube L30.

Recommended Uses

Use it in an M55.9 camera train where the published system chart specifies the Coupling (DT) — typically to reach a flattener or reducer's stated backfocus.

Compatibility and Accessory Notes

It threads onto Takahashi's M55.9 x 0.75 accessory standard. Takahashi's own documentation notes that this coupling and the M55.9 Extension Tube L30 cannot be screwed onto the female thread of the Camera Angle Adjuster S — worth checking against your system chart before ordering. Its 18 mm light path is what it adds to the optical train, not a caliper measurement of the physical part. The Takahashi Back Focus Guide tabulates this figure alongside every Takahashi telescope's back focus target.

Good to Know Before You Order

It does not thread onto the Camera Angle Adjuster S's female thread. Takahashi documents this specifically — if your train includes the Camera Angle Adjuster S, send us your full setup and we'll confirm what does fit.

Frequently Asked Questions

Is it difficult to set up?

No — it threads into the M55.9 chain directly, aside from the Camera Angle Adjuster S exception noted above.

What is it best used for?

Adding a fixed 18 mm of spacing in an M55.9 photo/visual train, per Takahashi's system chart.

Is it a visual-only part or does it work for imaging too?

Takahashi designates it "DT" for its photo/visual train, and it carries no optics, so it works the same mechanically in either use.

Bottom Line

An M55.9 coupling that adds a published 18 mm to the light path, built for Takahashi's DT photo/visual train — with the one Camera Angle Adjuster S exception worth checking first.