A riddle for photographers: “I write on two flash drives - does the shutter count twice?”

In the workshop, owners of advanced cameras with two slots (Nikon D750, D850, Z6 II, Z8) often handle fear: * “Master, I shoot weddings with duplication on 2 SD + CFexpress memory cards (Backup mode). It turns out that each flash drive records its own frame - and the shutter counter increases 2 times faster?

Let's look at how the camera firmware counts when duplicating.

How does the firmware calculate shooting when recording to 2 flash drives?

1. Physical shutter release (1 pulse):The shutter module raises and lowers the curtains **exactly once** for one frame.
2. Formation of metadata in a buffer (Buffer RAM):The EXPEED processor creates a single end-to-end frame in RAM and assigns it the current shooting number, for example `ShutterCount = 45 120`.
3. Recording to Slot 1 and Slot 2 cards:The camera duplicates the same generated file (with all metadata!) on both cards. The `ShutterCount` tag on both slots will be exactly the same - `45 120`.

The nuance of RAW mode on Slot 1 + JPG on Slot 2

Even if you write heavy RAW (NEF) to the first flash drive, and compressed JPG for the customer to the second - frame counter increases **by exactly 1 unit**. There is no doubling of mileage!

Table of modes of two card slots and EXIF ​​count

2-slot operating mode	Physical shooting of curtains	ShutterCount Tag Increment
Backup	1 shooting	+1 frame (Same on both cards)
RAW (Slot 1) / JPG (Slot 2)	1 shooting	+1 frame (End-to-end index)
Overflow	1 shooting	+1 frame (Sequential recording)