What is vignetting?

BBC Sky at Night Magazine's Scope Doctor Steve Richards answers your astronomy ailments.

A typical example of vignetting, taken through a 3-inch refractor Credit: Steve Richards

What is vignetting?

Vignetting is a reduction in image brightness at the edges of the field of view. There are two possible causes for this, the lens/mirror design or an obstruction in the light path.

Advertisement

Telescopes bend the light that passes through them, forming a cone of light that forms a circular image at the focus point but there is always a brighter central region in the cone leading to light fall-off towards the edges.

Single flat frames often show vignetting and artefacts of their own. Credit: Steve Richards
Single flat frames often show vignetting and artefacts of their own. Credit: Steve Richards

Anything that intrudes into the light cone will attenuate the light so telescope designers go to great lengths to produce focusers and adaptors with wide apertures.

If you’re finding errors in your field of view, read our complete guide to optical aberrations in your telescope and how to fix them.

Advertisement

Email Steve your astronomy queries to contactus@skyatnightmagazine.com and they could be answered in a future issue of BBC Sky at Night Magazine.