Takahashi TOA-150B 0.99x TOA-645 Field Flattener

Product Overview

The TOA-645 Field Flattener 150 Set is Takahashi's dedicated flattener kit for the TOA-150B refractor, built for high-resolution medium-format imaging. It holds the telescope's own 1100mm f/7.3 essentially unchanged — 1085mm at f/7.2 — while flattening the field across a Φ60mm image circle, large enough for today's full-frame and medium-format sensors.

Who It's For

This flattener suits TOA-150B owners shooting with large-format cameras — full-frame CMOS or medium-format backs — who need corner-to-corner sharpness across a wide sensor rather than a reduced focal length. Takahashi's own figures put the RMS spot diameter at 1 micron on-axis and 5 microns at the full 60mm diameter.

Key Features & Design

• Two-element flattener: two fully multi-coated elements in two groups, purpose-built for digital sensors rather than adapted from a film-era design.
• Φ60mm corrected image circle: covers full-frame and medium-format sensors with minimal fall-off.
• Near-native focal length: 1085mm at f/7.2 keeps the TOA-150B's own field of view essentially intact.
• Bundled CA35 (50.8) ring: included in this kit, matched to the TOA-150B's mount so the flattener installs as a complete system.

Optical / Mechanical Design

The flattener threads to the TOA-150B's 50.8 Adapter on an M72x1 male-to-female interface and outputs to the included CA35 ring on an M54x0.75 female thread. Total kit weight is 330g. The corrected back focus is 56.2mm measured from the CA35 ring — the figure to build the rest of your imaging train from. See the Takahashi Back Focus Guide for the full spacing chain.

Recommended Uses

High-resolution deep-sky imaging with full-frame or medium-format cameras on the TOA-150B; wide-field mosaicless framing of large nebulae and galaxy fields where the full Φ60mm circle is put to use; observatory and long-exposure narrowband work where field flatness across the whole sensor matters.

Compatibility and Accessory Notes

TOA-130NS and TOA-130NFB owners use the sibling kit, the TOA-645 Flattener 130 Set (TKA31587S), which bundles the same flattener with a CA Ring 130 sized for that telescope's mount instead of this kit's CA35 ring — we stock this listing for the TOA-150B specifically. The optical element itself is common to both kits.

Good to Know Before You Order

Sold as a complete kit: the CA35 ring is bundled with this flattener, so there's nothing separate to source to reach the 56.2mm back focus figure.

Built for the TOA-150B: if you own a TOA-130NS or TOA-130NFB instead, the matching kit is the TOA-645 Flattener 130 Set — get in touch and we'll point you to the right one.

Frequently Asked Questions

Is it difficult to set up?

No — it threads onto the TOA-150B's 50.8 Adapter and outputs directly to the included CA35 ring, which sets the 56.2mm back focus for you.

What is it best used for?

High-resolution astrophotography on the TOA-150B with full-frame or medium-format sensors, where a flat Φ60mm image circle matters more than a shorter focal length.

Does it reduce the focal length?

Barely — at 0.99x it holds the TOA-150B close to its native 1100mm f/7.3, landing at 1085mm f/7.2. It flattens the field rather than speeding up the system.

What's the difference between this and the TOA-35 Reducer?

This flattener keeps the focal length essentially native while widening the corrected circle to Φ60mm. The TOA-35 Reducer instead cuts the focal length to f/5.2 for a faster, narrower-circle system — the two serve different imaging goals on the same telescope.

Bottom Line

A complete TOA-150B flattener kit that holds the telescope near its native 1100mm focal length at f/7.2 while flattening a Φ60mm image circle for full-frame and medium-format imaging, with the matched CA35 ring included.