Nikon Z 8 Reference Manual page 430

Option
[HEIF primary
- HEIF
b
secondary]
D
Caution: "RAW Primary - JPEG Secondary"
If [ON] is selected for [Multiple exposure] > [Save individual pictures (RAW)] in the photo shooting
menu, or if [ON] is selected for [HDR overlay] > [Save individual pictures (RAW)] in the photo
shooting menu, unprocessed copies of the individual NEF (RAW) photos that make up each multiple
exposure or HDR picture will be recorded to both memory cards together with the JPEG composite,
regardless of the option selected for image quality.
Tip: When an Option Other than "Overflow" Is Selected
The shooting display and control panel show the number of exposures remaining on the card with
the least amount of space available.
The shutter release is disabled when either card is full.
Tip: Viewing Dual-Format Photos
Use the [Dual-format recording PB slot] item in the playback menu to choose the slot from which
dual-format photos are played back.
When viewing dual-format photos, you can view the other copy using [Jump to copy on other
card] in the i menu.
Tip: Recording Videos
The slot to which videos are recorded is selected using [Destination] in the video recording menu.
This option is available when [HLG] is selected for tone mode.
Two HEIF copies are recorded, one to each memory card.
The copy saved to the card in the primary slot is recorded at the image
quality and size selected in the photo shooting menu. The copy saved
to the card in the secondary slot is saved at an image quality of [JPEG/
HEIF basic] and a size of either [Medium] or [Small]. The size can
be selected by pressing 2 when [HEIF primary - HEIF secondary] is
highlighted.
At image qualities of RAW or RAW + JPEG/HEIF, this option is equivalent
to [Backup].
430
Description
Secondary Slot Function