There's viable optics up through x-rays; though they don't refract, they can still reflect at shallow angles, https://www.cosmos.esa.int/web/xmm-newton/technic

There's viable optics up through x-rays; though they don't refract, they can still reflect at shallow angles, https://www.cosmos.esa.int/web/xmm-newton/technical-details-mirrors https://www.cosmos.esa.int/web/xmm-newton/technical-details-... https://en.wikipedia.org/wiki/Wolter_telescope https://en.wikipedia.org/wiki/Wolter_telescope