There’s a reason why you can’t put a teleconverter on a cheap lens

Summary

Teleconverters, also known as extenders, are accessories placed between a lens and camera body to increase focal length. They contain extra glass elements that magnify the image, but this inevitably impacts image quality. Consequently, teleconverters perform best with high-quality, sharp lenses that can tolerate a slight degradation. Many teleconverters feature a protruding front element, making them physically incompatible with cheaper lenses that lack the necessary internal space. Additionally, the extra glass reduces light transmission, decreasing the lens's effective aperture by one to two stops depending on the teleconverter's magnification.

Key points

• Teleconverters increase focal length by adding glass elements between the lens and camera.
• Many teleconverters are incompatible with cheaper lenses due to a protruding front element.
• Extra glass in teleconverters reduces light transmission, slowing the effective aperture by one to two stops.