New main: Focal Reducers

A focal reducer is an optical accessory that is used to reduce the focal length of a telescope, resulting in a wider field of view and a faster focal ratio. By reducing the effective focal length of the telescope, the focal reducer can provide a wider field of view, making it easier to capture larger objects such as galaxies or nebulae, or to capture a wider portion of the sky.

Focal reducers typically consist of a lens or lens assembly that is placed in the optical path of the telescope, either at the focuser or at the back of the telescope. The lens is designed to reduce the effective focal length of the telescope while maintaining a flat field of view and minimising distortion or other optical aberrations.

In addition to providing a wider field of view, focal reducers can also make a telescope faster, meaning that it will have a lower f-number. This can be particularly useful for astrophotography, as a faster telescope allows for shorter exposure times and can reduce the effects of atmospheric turbulence.