Nikon D300 Complete Manual page 105

• Internal buffer memory space is limited. The D300 can
buffer up to 43 JPEG Fine Large images, but only 16
uncompressed 14-bit NEF images. The camera cannot
take additional pictures when the buffer is full. As images
are written to the CompactFlash card, buffer space is
freed. Any time that there is enough space remaining in
the buffer for an image, the camera can again take a
picture. When using the D300 set to a Continuous
shooting release shooting method, once the buffer is full
the camera slows, essentially to the speed at which it can
write a single image to the card (and on a D300, card
speeds are a factor in clearing the buffer).
• Internal buffer memory is temporary storage. Images in the
buffer are not accessible directly—only the camera's
electronics can touch the buffer memory—and until an
image is written to CompactFlash, your photo has not
been "saved." If power is completely lost with images in
the buffer, those images not yet moved to the storage card
are also lost. When the camera is writing data from the
internal buffer to the card a small green LED light on the
back of the camera is activated (it's labeled CF and is just
below and to the right of the Direction pad).
• Some controls impact buffer size. Specifically, both Long
exp. NR and High ISO NR reduce buffer size, as do
JPEG Compression set to Optimal Quality, ISO
sensitivities of H.03 or higher, Active D-Lighting turned
On, or Image Authentication turned On.
Why does the camera need an internal buffer? Well, the D300
has to deal with a large amount of raw data for each image
(~25MB for the largest NEF, ~350KB for the smallest JPEG).
Even at fast write speeds to CompactFlash permanent storage,
it takes a measurable amount of time to write these files from
the camera to the storage card. While JPEG images are much
smaller in size, the camera still has to create that image from
the original data, which also takes a small amount of time.
Without a buffer, the camera would force you to wait a large
amount of time between taking pictures. The buffer allows the
Thom Hogan's Complete Guide to the Nikon D300
V1.02
Page 105