Canon 640 lens spindle

Canon 640 lens spindle has built-in 1.4x magnifier, which also adopts DO lens technology. The real focal length is 585mm, the aperture is F4. 12, the radius of the imaging circle is 2 1.64mm, the length reaches 467.45mm, the back focal length is F5.77 mm, and there is room for installing an external magnifying glass. When the built-in magnifying glass is turned on, the focal length increases.