Collimate

You need to collimate the telescope.

Lead bricks were placed around the radioactive source so that the escaping gamma rays would be limited to a collimated beam rather than filling the lab.

I need to collimate my telescope so that the images are clearer.

However, after a bit of experience, the collimating chore can become routine.[…]Of course, if manufacturers made telescopes whose optics did not move around, you would only have to collimate a telescope once.

Binoculars can be collimated by either eccentric rings on the objective lenses or by tilting the prisms with grub screws (set screws).[…]Always collimate binoculars outdoors, or indoors by looking through an open window.

When calculating the size of the spot created on the retina by the lens of the eye when focusing the energy from a collimated source, the eye is generally considered to be ideal and diffraction limited.