Nikon D300 User Manual page 388

In programmed auto, the maximum aperture (minimum f-number) is
limited according to sensitivity (ISO equivalency), as shown below:
Maximum aperture at ISO equivalent of:
200 400 800 1600 3200
5 5.6
7.1
8 10
For each one-step increase in sensitivity (e.g., from 200 to 400), aperture is
stopped down by half an f-stop. If the maximum aperture of the lens is
smaller than given above, the maximum value for aperture will be the
maximum aperture of the lens.
When an SC-series 17, 28, or 29 sync cable is used for off-camera flash
photography, correct exposure may not be achieved in i-TTL mode. We
recommend that you choose spot metering to select standard i-TTL flash
control. Take a test shot and view the results in the monitor.
In i-TTL, use the flash panel or bounce adapter provided with the flash
unit. Do not use other panels such as diffusion panels, as this may
produce incorrect exposure.
~
Use Only Nikon Flash Accessories
Use only Nikon Speedlights. Negative voltages or voltages over 250 V
applied to the accessory shoe could not only prevent normal operation,
but damage the sync circuitry of the camera or flash. Before using a Nikon
Speedlight not listed in this section, contact a Nikon-authorized service
representative for more information.
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