Nikon D300 User Manual page 115

mirroring. Since your camera is very much a computer, a
function like this is great to have. Be sure that both cards
are of equal capacity or that the secondary card is larger
than the primary when you use this function. Otherwise,
you'll have reduced capacity shown for the primary card.
Since the camera is required to write a duplicate image
to each card, the smallest card in the two slots sets the
maximum capacity of the camera's storage.
▪ RAW primary, JPEG secondary – For those who like to
shoot NEF (RAW) files, this function can save some
time. You'll have a JPEG for immediate use and a RAW
file for later post-processing. When you take a picture,
the camera will write the RAW file to the primary card
and a JPEG file to the secondary card. There is no choice
in this arrangement—RAW always goes to primary and
JPEG to secondary. Also, this function only works as
described when you have Shooting Menu > Image
quality set to some form of NEF (RAW) + JPEG. If you
set Image quality to just NEF (RAW) or JPEG fine
alone—instead of NEF (RAW) + JPEG fine—the
camera will simply write a duplicate file to both cards
instead of a RAW on one and a JPEG on the other. In
other words, if Image quality is set to NEF (RAW), the
camera will write two NEF files; if set to JPEG, two JPG
files; and if set to TIFF (RGB), two TIF files—one on
each card. Basically, unless you set Shooting Menu >
Image quality to some form of NEF (RAW) + JPEG, this
function acts like the Backup function mentioned
previously.
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