From Takahashi Japan . . .
FOA-60 field flattener with two groups of two lenses corrects the peripheral aberration of the main focus and at the same time shortens the focal length to 495 mm (f / 8.2) 0.93 times. A uniform star image with SPOT diameter within 10 microns can be obtained up to the full size periphery, so it is somewhat dark with f / 8, but it can be used for Hoshino shooting. In taking the total solar eclipse, the focal length is just right for shooting the external corona. It is also suitable for photographing terrestrially, such as wild birds, as an ultra-high performance telephoto lens of about 500 mm (f / 8).