Nikon D720 User Manual page 331

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Recognizing CPU and Type G, E, and D Lenses
CPU lenses (particularly types G, E, and D) are recommended, but note
that IX-NIKKOR lenses can not be used. CPU lenses can be identified by
the presence of CPU contacts, type G, E, and D lenses by a letter on the
lens barrel. Type G and E lenses are not equipped with a lens aperture
ring.
CPU contacts
CPU lens
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AF-S/AF-I Teleconverters
If the combined aperture when the camera is used with
an AF-S/AF-I teleconverter is slower than f/5.6 but is
equal to or faster than f/8, autofocus and electronic
rangefinding will be available only with the center focus point and the
camera may be unable to focus on dark or low-contrast subjects.
Single point AF is used when 3D-tracking or auto-area AF is selected
for AF-area mode (0 86). Autofocus is not available if teleconverters
are used with the AF-S VR Micro-Nikkor 105mm f/2.8G IF-ED. If
TC-17E II, TC-20E, TC-20E II, or TC-20E III teleconverters are used with
the AF-S NIKKOR 300mm f/4E PF ED VR, autofocus is available only in
AF-S mode.
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Lens f-number
The f-number given in lens names is the maximum aperture of the
lens.
Type G/E lens
Aperture ring
Type D lens
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