CFe/SD card logic

[Thom Hogan]

This has probably been done to death since the Z6ii came out, but I'm struggling to find the best answer...

I'm a part-time pro that mainly does events. I still have my trusty D750 that I'm about to chop in for a Z6iii.

Now, the Z6ii/iii has dual slots of course, and everyone says that there's no point messing around with ancient SD cards as the CFe is so much faster etc. Which I get. But from what I understand, if you use the SD card in backup mode, the speed will be limited to the slowest card.

The answer isn't as obvious as many want it to be.

First a couple of facts: (1) there is no SD card as fast as CFe cards now are; (2) yes, the camera is "only as fast as the slowest card"; and (3) SD cards come in a lot of different "flavors."

Let's work backwards.

#3 — Use only UHS II cards, and Video Class 3 and as close to 300Mbps as possible. This is basically the fastest type card the current Nikon bodies can use. You limit #2 by this.

#2 — "only as fast" is unfortunately a generalization that isn't clear. If you take one image at a time (no continuous Release Mode), you're not likely to ever see a "slow" card slowing down the camera (though I'll have more to say about that in a bit). If you use Continuous High Extended at top speed, you're likely to see something happen: the buffer will be smaller. That's particularly true if you're using NEF and Backup as your choices. It's less true if you're using NEF+JPEG with each going to a different slot.

#1 — Where I see most people getting into trouble is they say "hey, I have some SD cards, I'll just use those." But that card is UHS I, or worse, not even UHS. It's probably 95Mbps top speed or slower.

Thom's Axiom #237 is "always buy new, top end cards with a new camera. Retire your old cards." First, memory cards don't last forever. The chances of a card error ruining an image rises as the card ages out in its NAND cells. Memory cards can be read almost forever, but they can't be written to past a certain number of cell writes.

Now, as to slowing down a camera. There's a silly little aspect that comes into play: size of card. Whenever the camera needs to access the card, such as when you press the playback button, it does an assessment of the FAT/directory status. The bigger the card, the longer that takes. It's not as big a problem today with faster cards, but in the D500/D850 era it was very common to see someone put a 64GB card in the XQD slot and a 512GB card in the SD slot. The camera needs to check 64GB+512GB before it starts displaying something. Take the SD card out, and playback seems inherently faster.

This is less true now with the faster cards, but it still applies. I wouldn't be using a smaller but fastest CFe card coupled with a 1TB+ SD card, for instance.