Teleconverters and aperture factors – f stop.

300mm f4 lens with 1.4x converter produces f5.6.

Excerpt from

The teleconverter reduces the maximum aperture of the lens by one stop (1.4x converter), 1.5 stops (1.7x converter) or 2 stops (2x converter). An f/4 lens becomes an f/5.6 lens with a 1.4x mounted. An f/5.6 lens becomes f/8.

  • Teleconverters work very well with f/4 or f/2.8 telephoto prime lenses (300, 400, 500, 600), especially mounted on a tripod.
  • Teleconverters work acceptably on high quality zoom lenses with maximum apertures of f/2.8 or f/4.
  • Teleconverters don’t work well with consumer (f/5.6 zooms), medium range zooms, or wide angle lenses. Most manufacturer’s teleconverters won’t even mount to such lenses.
  • Third party (Sigma, Kenko) teleconverters will mount to other lenses that the manufacturer’s teleconverters won’t mount to.
  • Third party teleconverters don’t ‘report’ electronically to the camera body and may ‘fool’ the body into trying to autofocus when it shouldn’t. Results are pretty variable (often poor).

f stop chart

About janpenguin

Email: k2.mountain [at] gmail [dot] com Every content on the blog is made by Free and Open Source Software in GNU/Linux.
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