SUMMARY
Teleconverters are accessories that increase the focal length of a lens, effectively providing more zoom. However, their use typically results in a reduction of image quality, most notably in terms of sharpness. Additionally, teleconverters decrease the maximum aperture of the lens, which can impact low-light performance and depth of field control.
TAKEAWAYS
Teleconverters extend lens focal length.
Image sharpness is often reduced when using teleconverters.
Teleconverters decrease the lens's maximum aperture.