The Takahashi 67-Flattner for the TOA-XXX is designed for large format cameras. The flattener consists of 2 groups of mulit-coated ED glass. The image circle produced is 92 mm in diameter, with 3 micron stars at the center and 20 micron stars at the edge.
The newly designed 645 flattener features two fully multi-coated lens elements in two groups and provides outstanding correction out to a 60 mm image circle. Being designed specifically for the TOA-130N and TOA-150B, RMS spot diameters of 1 micron on-axis are achieved. At a 30 mm diameter image circle, the RMS spot diameter is 2 microns, and at 43 mm it is 3 microns. Even out to the full diameter of 60 mm, the RMS spot diameter is 5 microns. With these spot sizes, images are nearly aberration on even the newest small pixel sensors.
The flattener is available in two versions, one for the TOA-130N and one for the TOA-150B. Optically, the two versions are identical, with the only difference being the length of the spacer on the camera side of the adapter. Unlike the old 67 flattener, the 645 flattener has an M72 thread on the telescope side, meaning it can be used not only on the TOA-130NFB, but on the TOA-130NS as well.
For the TOA-130N with the included adapter ring (L), the flattener has a male M72 facing the telescope and a female M54 facing the camera. The metal back distance from the M54 thread is 56.2 mm. If you remove the adapter ring (L), the camera can interface with a female M72 thread with a metal back distance of 83.7 mm.
For the TOA-150 with the included adapter ring (S), the flattener has a male M72 facing the telescope and a female M54 facing the camera. The metal back distance from the M54 thread is 56.2 mm. If you remove the adapter ring (S), the camera can interface with a female M72 thread with a metal back distance of 73.9 mm.