How does a teleconverter change lens characteristics?

For Nikon bodies we have had teleconverters that are 1.25x, 1.4x, 1.6x, 1.7x, 2x, and 3x available from Nikon or other vendors. Here are the changes each makes:

Note: “focal length changes” means that the equivalent angle of view decreases and the focal length changes by the specified amount (otherwise known as “equivalent” focal length).

1.25x converter (TC800-1.25E ED)

  • Focal length changes by 1.25x
  • Aperture increases by 2/3 stop
  • Example: 800mm f/5.6 lens becomes 1000mm f/7.1

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 always made on the new changed focal length and aperture values. 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, D7200, D500, D600, D610, D750, D800, D810, D4, D4s, and D5. 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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