Takahashi TOA-645 Flattener 0.99x for TOA-130NS/NFB

Product Overview

The TOA-645 Flattener is Takahashi's large-format field corrector for the TOA-130NS and TOA-130NFB, holding the focal length essentially unchanged at 990mm f/7.6 while opening the corrected image circle to 60mm — large enough for today's bigger CMOS sensors. Two lens elements in two groups thread between M72 x 1 male and female interfaces, in a compact 78mm diameter, 42mm long, 265 g housing.

Who It's For

This is a good match if you own a TOA-130NS or TOA-130NFB and are imaging with a large-format CMOS sensor where the older 67-series flatteners and the 40mm-circle TOA-35FL fall short of full corner coverage.

Key Features & Design

• 60mm corrected image circle: built for large modern CMOS sensors rather than the 40mm circle of the TOA-35FL.
• Near-unity focal ratio change: 1000mm f/7.7 native becomes 990mm f/7.6 — correction with almost no reach traded away.
• Tight spot diagrams: Takahashi publishes 1 micron RMS on-axis, rising to 5 microns at the full 60mm diameter.
• M72 x 1 threads on both sides, in a compact 78mm x 42mm housing at 265 g.

Optical / Mechanical Design

Where the TOA-35FL corrects the TOA-130NS/NFB to a 40mm circle, the TOA-645 uses two lens elements in two groups to hold correction out to 60mm, addressing the larger sensor formats that have become common since the earlier 67-series flatteners were designed. Takahashi states the newer design performs nearly aberration-free with today's smaller pixel pitches, where the older flatteners show their age.

Recommended Uses

Full-frame and medium-format CMOS deep-sky imaging on the TOA-130NS or TOA-130NFB, where corner correction across a 60mm circle is required.

Compatibility and Accessory Notes

Takahashi publishes this flattener for the TOA-130NS/NFB.

The TOA-150B takes the same optical design in a separate kit, part TKA32587S, which Ontario Telescope lists separately — the two are not interchangeable at the mechanical level despite sharing the optical formula. For smaller-sensor use, the 40mm-circle TOA-35FL is also available. Full spacing detail is in the Takahashi Back Focus Guide.

Good to Know Before You Order

Not interchangeable with the TOA-150B kit: that telescope uses its own TOA-645 flattener kit (TKA32587S) rather than this TOA-130-specific part.

Built for imaging: the corrected field has no benefit for eyepiece observing.

Frequently Asked Questions

Is it difficult to set up?

No — it threads between M72 x 1 interfaces with a fixed 56.2mm back focus, so there is no spacing to calculate.

What is it best used for?

Full-frame and large-format CMOS deep-sky imaging on the TOA-130NS or TOA-130NFB.

How is this different from the TOA-35FL?

The TOA-35FL corrects a 40mm image circle; the TOA-645 corrects out to 60mm for larger sensors, at nearly the same resulting focal length.

Does this fit my TOA-150B?

The TOA-150B uses its own TOA-645 flattener kit rather than this part; send us your telescope model and sensor size and we will confirm which flattener you need.

Bottom Line

The TOA-645 Flattener corrects the TOA-130NS/NFB to a 60mm image circle at essentially its native 990mm f/7.6, built for the large CMOS sensors that have outgrown the older 40mm-circle flatteners.