Primary Slot Selection; Secondary Slot Function - Nikon D850 Menu Manual

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Extensions
The following extensions are used: ".NEF" for NEF (RAW) images, ".TIF"
for TIFF (RGB) images, ".JPG" for JPEG images, ".MOV" for MOV movies,
".MP4" for MP4 movies, and ".NDF" for dust off reference data. In each
pair of photographs recorded at image-quality settings of NEF
(RAW)+JPEG, the NEF and JPEG images have the same file names but
different extensions.

Primary Slot Selection

Choose the primary slot for shooting and playback. Select XQD
card slot to designate the card in the XQD card slot as the
primary card, SD card slot to choose the SD card.

Secondary Slot Function

Choose the role played by the primary and secondary cards
when two memory cards are inserted in the camera.
Choose from Overflow (the secondary card is used only when
the primary card is full), Backup (each picture is recorded to
both the primary and secondary card), and RAW primary - JPEG
secondary (as for Backup, except that the NEF/RAW copies of
photos shot at settings of NEF/RAW + JPEG are recorded only to
the primary card and the JPEG copies only to the secondary
card).
G button ➜ C photo shooting menu
G button ➜ C photo shooting menu
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Menu Guide