Takahashi TOA-35FL 2.7" Flattener for TSA-120/TOA-130/TOA-150B

Product Overview

The TOA-35FL is Takahashi's 2.7-inch field flattener for the TSA-120 and TOA-130/150 triplet apochromats. It threads onto a 2-inch drawtube and presents a 2-inch female output, correcting the field to a 40mm image circle with essentially no edge distortion, at a published weight of 200 g.

Who It's For

This is a good match if you own a TSA-120, TOA-130NS/NFB, or TOA-150B and are imaging with a CCD or CMOS sensor up to full-frame, where corner star shape needs correcting that the native triplet design does not fully address on its own.

Key Features & Design

• Shared across three telescopes: the same part flattens the field on the TSA-120, TOA-130NS/NFB, and TOA-150B, each with its own resulting focal length.
• 40mm corrected image circle: covers virtually all common CCD and CMOS sensor sizes without edge-of-field distortion.
• 117.5mm back focus held constant across all three host telescopes.
• Compact 2-inch in-line design: 60mm diameter, 74mm long, 200g.

Optical / Mechanical Design

The TOA and TSA triplet apochromats are corrected for a flat visual field but benefit from a dedicated flattener when imaging across a full sensor. The TOA-35FL sits between the 2-inch drawtube and the camera train, trimming the focal length by a small, telescope-specific amount while holding the 40mm image circle and 117.5mm back focus fixed regardless of which of the three host telescopes it is mounted on.

Recommended Uses

Full-frame and APS-C deep-sky imaging on the TSA-120, TOA-130NS/NFB, or TOA-150B where flat corner stars are required across the sensor.

Compatibility and Accessory Notes

Takahashi publishes this flattener for three telescopes.

For sensors larger than 40mm, Takahashi's TOA-645 flattener line covers TOA-130 and TOA-150B with a 60mm image circle instead — see the Takahashi Back Focus Guide for the full spacing picture.

Good to Know Before You Order

40mm image circle, not full-format: larger sensors needing a 60mm circle should look to the TOA-645 flattener line instead of this part.

Built for imaging: the flattened field has no benefit for eyepiece observing, where the native triplet field is already flat enough.

Frequently Asked Questions

Is it difficult to set up?

No — it threads onto the 2-inch drawtube and presents a fixed 117.5mm back focus on the camera side, so there is no spacing to calculate.

What is it best used for?

Flat-field deep-sky imaging on the TSA-120, TOA-130NS/NFB, or TOA-150B.

Does it fit sensors larger than APS-C?

Its 40mm image circle covers most full-frame sensors; for larger formats, Takahashi's TOA-645 flattener (60mm circle) is the better match — send us your sensor size and we will confirm which one you need.

Is the same part used on all three telescopes?

Yes — one flattener, with a slightly different resulting focal length on each host telescope.

Bottom Line

The TOA-35FL is a single 2.7-inch flattener that corrects the field to a 40mm image circle at a fixed 117.5mm back focus across the TSA-120, TOA-130NS/NFB, and TOA-150B.