An x-ray optical system includes a multiple corner optic assembly including an adjustable aperture assembly located in close proximity to the optic assembly. The adjustable aperture assembly enables a user to easily and effectively adjust the convergence of an incident beam of x-rays or the optic focal spot size. The adjustable aperture assembly may further enable a user to condition x-rays of one wavelength and block x-rays of another wavelength and thereby reduce the amount of background radiation exhibited from x-rays of more than one wavelength.