Nikon Tele converters (TC)
Additional info/ modifications on what sir Rhedd mentioned above
Light loss is directly proportional to the teleconverters magnification power. When i use my 1.4x TC on my 70-200 f2.8, it becomes a 98-280mm f4 lens experiencing a loss of 1-stop. Using a 1.7 TC will result in a maximum aperture of f4.8 or a loss of 1 1/2 stop and a 2.0x TC will render max aperture to f5.6 or a 2-stop loss. Light losses resulting from reduction in max aperture needs to be compensated by dialing in slower shutter speeds or boosting ISO. In bright settings, this won't be a problem.
Not all fast Nikon primes will function well with the Nikon TCs. An example is the popular 105mm f2.8 VR Macro. You can use the TCs on this glass but you will lose Autofocus capability.
For f/4 lenses, when using 1.7x or 2x TCs, there will be no AF except when using the newer bodies with f/8 support like the D4, D600, D800/800E and D7100. Older bodies usually lose full AF capability with aperture settings smaller than f/5.6 (larger f-stop number). AF is ok with a 1.4x TC on all bodies.
makiki share lang po TEAM D5100 :))