How does a teleconverter change lens characteristics?

For Nikon bodies we have had teleconverters that are 1.4x, 1.6x, 1.7x, 2x, and 3x available. Here are the changes each makes:

1.4x converter (TC-14a, TC-14b, TC-14e, third party converters)

  • Focal length changes by 1.4x
  • Aperture increases by one stop
  • Example: 200mm f/2 lens becomes 280mm f/2.8


1.6x converter (TC-16a)

  • Focal length changes by 1.6x
  • Aperture increases by 1.3 stops
  • Example: 200mm f/2 lens becomes 320mm f/3.2


1.7x converter (TC-17e)

  • Focal length changes by 1.7x
  • Aperture increases by 1.5 stops
  • Example: 200mm f/2 lens becomes 340mm f/3.5


2x converter (TC-201, TC-301, TC-20e, third party converters)

  • Focal length changes by 2x
  • Aperture increases by two stops
  • Example: 200mm f/2 lens becomes 400mm f/4


3x converter (no Nikon converters; Kenko Pro 300)

  • Focal length changes by 3x
  • Aperture increases by three stops
  • Example: 200mm f/2 lens becomes 600mm f/5.6


DOF and other calculations are made on the new effective focal length and aperture. Thus, a 2x on a 200mm f/2 lens would cause the combination to function exactly like a 400mm f/4 lens (200mm x 2 = 400mm, two stops smaller than f/2 is f/4).


Note that the aperture must be f/8 or faster (after adjustment due to the TC) for the following cameras for autofocus to work: D7100, D600, D800, and D4. For all other Nikon DSLRs, the aperture must be f/5.6 or faster (after adjustment due to the TC) for autofocus to work. 

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