What is Distortion in Telescopes?

Distortion is an optical aberration, resulting in a difference in magnification across your field of view. This aberration does not affect optical focus but causes your image to appear curved.

What Causes Distortion?

Distortion is caused by light hitting curved lenses. Because the lens is curved, light travels a different distance from the edge to the center of your field of view. This causes the magnification to appear either stronger or weaker as you near the edges, creating a curved effect.

Which Telescopes Experience Distortion?

Distortions can appear in any telescope, depending on the curvature of the lens. This aberration is most prevalent in telephoto lenses and wide-angle eyepieces. In telephoto lenses, both concave and convex lenses are used. Because of the stronger negative curvature, the magnification is increased toward the edges of the image. In wide-angle eyepieces, the opposite occurs. Convex lenses are used to increase magnification in the center of the image when observing wide fields of view.

What are the Types of Distortion in Telescopes?

There are two types of optical distortions in telescopes: pincushion and barrel. Pincushion distortions occur in concave lenses, like telephoto lenses. Because magnification is stronger at the edges than at the center, the image appears to bend inward. Barrel distortions tend to occur in wide fields of view. These lenses causes the magnification to be stronger at the center, curving the image in the opposite direction.

How to Fix Distortion in Telescopes

Because distortion is most prevalent in wide fields of view, this isn’t too problematic for astronomy. This is because telescopes typically have small fields of view. If you do find unwanted curvature, you can use a narrow-field eyepiece. When taking photos of space, distortions may become more noticeable. This can be reduced or resolved using photo editing tools such as LightRoom’s Lens Correction tool.