Nikon D750 User Manual page 265

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Focal Length Not Listed
If the correct focal length is not listed, choose the closest value greater
than the actual focal length of the lens.
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Teleconverters and Zoom Lenses
The maximum aperture for teleconverters is the combined maximum
aperture of the teleconverter and the lens. Note that lens data are not
adjusted when non-CPU lenses are zoomed in or out. The data for
different focal lengths can be entered as separate lens numbers, or the
data for the lens can be edited to reflect the new values for lens focal
length and maximum aperture each time zoom is adjusted.
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