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.
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.