Nikon D700 User Manual page 89

[I_ Auto DX Crop
The Fnbutton can not be used to select image area when a DX lens is
attached and Auto DX crop is on.
[] The Fn, Depth-of-Field Preview, and AE-L/AF-L Buttons
Changes to image area settings can be made using the Fnbutton (the
default setting, see Custom Setting fS, Assign FUNC. button, pg. 320), the
depth-of-field preview button (Custom setting f6, Assign preview
button, pg. 324), or the AE-//AF-/button (Custom Setting f7, Assign AE-L/
AF-L button, pg. 325). Note that some "button press" options can not be
combined with options using "+dials:'
[] Image Size
Image size varies with the option selected for image area.
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