D700 vs Df: same exposure settings but 0.9 stops file exposure difference

Started Dec 24, 2013 | Discussions thread
Horshack Veteran Member • Posts: 5,803
Check the aperture lever on your D700

The Nikon F-Mount controls the aperture on lenses via a mechanical lever that couples to a slider on the lens. The tolerances for the F-Mount lever are pretty exacting and if the lever gets bent (not that unusual) then the indicated aperture will no longer match the actual lens aperture. Most of the time a bent aperture will cause the lens to fail to stop down rather than stopping down too much, which means if it is the lever it's likely the one on your D700 that is bent/out-of-spec since it's producing +.9EV brighter exposures than your Df.

There are a few easy ways to check the calibration of the lever. The first is to shoot both bodies wide-open and see if the exposure matches, since the coupling doesn't have to stop the lens down for wide-open apertures. Another way is to take each body and shoot wide-open and then stopped down 1EV (f/2.8 -> f/4 in your case) at the same shutter speed/ISO - the exposure of the f/4 image should be -1EV the f/2.8, and more importantly you should see the DOF difference (shoot a subject near MFD to make the DOF difference more noticeable); if not then the lever is not stopping down appropriately.

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