A reflecting telescope's primary mirror focal point. Astronomers place cameras at prime focus to record bright, wide field images.

The location at which the main lens or mirror of a telescope focuses an image without being reflected or refocused by another mirror or other optical element.

The point in a reflecting telescope where the mirror focuses incoming light to a point.

When the eyepiece is removed from a telescope and replaced with a camera body it is said to be at prime-focus. It is the point at which a telescope's optics direct incoming light. back to the top

Prime focus imaging involves attaching a camera directly to a telescope without any intermediate eyepiece or camera lens. This is as opposed to afocal imaging which uses an eyepiece or eyepiece and camera lens to increase the magnification (such as for planetary imaging). Prime focus imaging is the normal setup used for deep-sky astrophotography as it allows wider fields of view and faster focal ratios.

The point in a telescope where the objective focuses the light.

Attaching a telescope to an SLR camera to make it a telephoto lens. Not all telescopes can be set up this way.

The point at which the primary mirror or lens of the telescope mirror forms an image of a distant object.