Buying memory cards can feel oddly stressful. There are numbers everywhere, lots of “up to” claims, and a quiet fear that buying the wrong one will somehow ruin your photography.
It won’t. But there are a few things that genuinely matter - and a lot that doesn’t.
1) Your camera sets the rules (UHS-I vs UHS-II)
SD cards use something called a UHS bus. Think of it as the speed limit between your camera and the card.
- UHS-I → up to ~104 MB/s
- UHS-II → up to ~312 MB/s (extra row of pins)
- UHS-III → technically faster, rarely relevant in real life
Here’s the important bit:
Your camera can only use the speed it supports. A faster card doesn’t make an older camera faster.
If your camera only supports UHS-I, a UHS-II card will still work, but it will behave like a UHS-I card in-camera.
2) Ignore “up to” speeds — look for sustained write speed
The big headline number on packaging is often a best-case maximum read speed. It’s not useless, but it’s not the number that affects your actual shooting.
What matters most for photography is sustained write speed - how fast the card can keep writing without slowing down.
This affects:
- how quickly your camera clears its buffer
- how long you can shoot bursts
- whether video recording is stable
3) The marking that matters: Video Speed Class
Look for Video Speed Class on the card. This is a more honest indicator of sustained write speed.
- V30 → sustained 30 MB/s (solid baseline for most people)
- V60 → sustained 60 MB/s (useful for heavier video / faster buffer clearing)
- V90 → sustained 90 MB/s (specialist and expensive)
For most photographers, especially if you shoot photos and edit in Lightroom, V30 is absolutely fine.
4) RAW shooters: why this matters
If you shoot RAW (and especially wildlife or sports), file sizes are larger and bursts fill buffers faster. That’s when you feel the difference between “marketing speed” and “real sustained speed”.
A sensible baseline choice for stills is:
- reputable brand
- UHS-I (if that’s what your camera supports)
- V30
5) When UHS-II can still be worth it (even if your camera is UHS-I)
There’s one exception where buying a faster card can make a difference even if your camera can’t use the full speed:
Faster transfers to your computer
If you use:
- a UHS-II card, and
- a UHS-II card reader
…your downloads to your laptop can be noticeably faster. If you shoot a lot (hello, me too), that can be a genuine quality-of-life upgrade.
But it’s about workflow, not shooting performance.
6) Card size: bigger isn’t always better
Big cards feel safer. In reality, they can be riskier.
If one huge card fails or corrupts mid-shoot, you lose everything.
A practical middle ground is:
- two smaller cards (e.g., 2×64GB or 2×128GB)
- rather than one massive card
You also get a natural break point and an extra layer of insurance.
7) Speed matters more than size
If you’re choosing between:
- a very large, slower card, and
- a slightly smaller, faster card
Choose speed. You’ll feel it when your buffer clears quickly - and you won’t miss the extra capacity as much as you think.
8) The short version
- Buy what your camera can actually use
- Ignore “up to” marketing numbers
- Look for V30 as a solid baseline
- Use more than one card if you can
- Faster transfer speed ≠ faster shooting
Next in the series
In the next post I’ll show my real-life setup on the Nikon D750: two card slots, mixing cards, and how I use RAW + JPEG without buying the most expensive option on the shelf.