Fast SD and CFexpress Cards for RAW Burst: The Speed Playbook

Ever held down the shutter expecting a blazing 20–30 fps RAW burst, only to watch your camera stutter after a second or two? That cliff you hit is often your memory card, not your camera. RAW frames are massive, and once the internal buffer fills, your camera can only go as fast as the card can write. That’s why “fast” isn’t a marketing adjective here, it’s a bottleneck you can measure, manage, and fix with the right card and setup.

In this guide, I’ll break down what “fast” really means for SD and CFexpress, how to size a card for your camera and shooting style, and the settings that keep your burst rate high when it matters.

Why Cards Decide Your Burst Speed

Modern bodies push truly wild burst rates. But the pipeline is simple:

• Sensor → Processor → Buffer (fast RAM) → Card

The buffer buys you a short sprint. Once it’s full, throughput is limited by the slowest link left: the card. If your card can’t keep up with the data being generated, your frame rate drops until the buffer starts clearing.

Here’s the uncomfortable math:

• Average RAW size × fps = required sustained write throughput

For a 45 MP camera shooting 14‑bit lossless RAW at about 50 MB per file:

• 50 MB × 20 fps = 1000 MB/s (≈1 GB/s)

Even the best UHS‑II SD cards can’t touch that. Most cameras that advertise 20–30 fps RAW do it via buffer, and rely on CFexpress (Type B or A) for longer sustained bursts. If your camera is SD‑only, the right card still matters, but you’ll be optimizing buffer clear speed and recovery more than truly “limitless” bursts.

SD vs CFexpress: What’s the Real Difference?

SD Cards

• Buses: UHS‑I (104 MB/s), UHS‑II (312 MB/s). UHS‑III and SD Express exist but aren’t widely supported in cameras.
• Speed classes to know:
• U3: minimum 30 MB/s (floor)
• V30/V60/V90: minimum sustained 30/60/90 MB/s
• Reality check: “300 MB/s” on the label is typically peak read. Sustained writes for good UHS‑II V90 cards often land 150–260 MB/s in-camera, and much lower for V30/V60.

CFexpress

• Types:
• Type B (most common, same form factor as XQD), PCIe-based, very high throughput
• Type A (Sony bodies), smaller, slower than Type B but much faster than SD
• Generations: CFexpress 2.0 (PCIe Gen3) vs 4.0 (PCIe Gen4). Cards are backward compatible, but camera controllers often cap speeds to Gen3 performance.
• Important rating: VPG (Video Performance Guarantee), especially VPG400 = ≥400 MB/s sustained. Even for stills, this “sustained” guarantee is gold for long bursts.

The Bottom Line

• If your camera supports CFexpress Type B, it’s the right tool for RAW bursts.
• If your camera supports CFexpress Type A, it’s still a big upgrade over SD.
• If your camera is SD‑only, buy top-tier UHS‑II V90 and mind your settings.

How to Calculate the Speed You Actually Need

Use this as your starting point:

• Required MB/s ≈ average RAW MB × desired fps (after the buffer is full)

Then reality‑proof it:

• Multiply by 0.8 to account for overhead and camera/controller inefficiency.
• If you use lossless compressed RAW, your per‑file size may drop 25–50% (varies). Check your actual files.
• Some cameras drop bit depth or compress more at high fps. This helps.

Examples:

• 24 MP body, ~25 MB RAW, want 10 fps for sustained action:
• 25 × 10 = 250 MB/s; safety factor → ~200 MB/s needed
• A strong UHS‑II V90 SD card can be enough (but pick a proven one).
• 45 MP body, ~50 MB RAW, want 15 fps beyond buffer:
• 50 × 15 = 750 MB/s; safety factor → ~600 MB/s needed
• SD won’t do it; CFexpress Type B is required.

Camera Bottlenecks You Can’t Ignore

• Camera write cap: Many bodies cap card throughput. It doesn’t matter if your card can do 1500 MB/s if your camera tops out at 500 MB/s.
• Dual-slot penalty: Writing “Simultaneous/Backup” to SD and CFexpress forces the camera to the speed of the slower slot. For action, switch to “Card 1 only” or “Relay” if you need capacity, not mirroring.
• Firmware matters: Body updates often improve buffer handling and card compatibility. Check for updates before a big shoot.

Choosing the Right Card Type for RAW Burst

If Your Camera Uses CFexpress Type B

• Look for:
• High sustained write specs (not just peak).
• VPG400 certification when available.
• Cards marketed for sustained performance (“Cobalt,” “Black,” “AV PRO,” “DIAMOND” tiers).
• Good thermal design; CFexpress can throttle if hot.
• Typical sustained write you’ll see in-camera on modern bodies:
• 400–900+ MB/s (camera-dependent).
• Good families to research:
• ProGrade Digital CFexpress Type B Cobalt (known for high sustained writes)
• Lexar Professional CFexpress Type B DIAMOND (VPG400)
• Angelbird AV PRO CFexpress Type B (robust sustained, vendor tools/firmware)
• Delkin BLACK CFexpress Type B (sustained performance focus)
• SanDisk Extreme Pro CFexpress Type B (widely supported)
• Wise Advanced CFexpress Type B (pro workflows)
• Tip: Bigger capacities often sustain peak speeds longer due to larger internal parallelism and cache.

If Your Camera Uses CFexpress Type A (ProGrade)

• Expect lower sustained writes than Type B, but still far above SD.
• Prioritize:
• High sustained write claims and proven testing.
• Thermal robustness (Type A cards run hot in compact bodies).
• Families to research:
• Sony TOUGH CFexpress Type A
• ProGrade CFexpress Type A Cobalt
• Delkin BLACK CFexpress Type A
• Reality: Expect sustained writes broadly in the low‑to‑mid hundreds of MB/s; your camera’s controller is usually the cap.

If Your Camera Is SD-Only (UHS-II)

• Mandatory: V90 for consistent burst performance.
• Ignore read‑speed marketing; look for tested sustained write numbers and V90 certification.
• Families to research:
• Sony TOUGH SF‑G (UHS‑II V90)
• ProGrade UHS‑II V90 (Gold/V90 series)
• Lexar Professional 2000x UHS‑II (V90 variants)
• SanDisk Extreme Pro UHS‑II V90
• Delkin Power/Black V90
• Angelbird AV PRO SD V90
• Expect ~150–260 MB/s sustained in-camera with the best cards, depending on body.

Mixed Slots: Don’t Let SD Handcuff CFexpress

Many bodies pair CFexpress Type B with SD as the second slot. If you set the camera to:

• “Simultaneous/Backup”: Your sustained fps after buffer = limited by the SD card’s write speed.
• “RAW to CFexpress, JPEG to SD”: You’ll still take a hit, depending on JPEG rate and size.

For peak bursts:

• Use CFexpress only.
• Or set slots to “Relay” (overflow), not backup.

Avoid These Common Speed Traps

• Confusing peak with sustained: Peak “W: 800 MB/s” means nothing if the card falls to 200 MB/s after its cache. Look for sustained numbers and certifications (VPG400, V90).
• Counterfeits: High‑end cards are heavily counterfeited. Buy from authorized dealers. Verify serials via the manufacturer’s utility if offered.
• MicroSD with adapters: MicroSD rarely meets UHS‑II requirements; most are UHS‑I V30. Don’t hobble your camera.
• Not formatting in-camera: Always format cards in the camera you’ll shoot with. It ensures the file system layout your body prefers.
• Neglecting firmware: Some CFexpress cards and many cameras receive firmware to fix compatibility and throttling issues.
• Running cards near thermal limits: CFexpress can throttle under heat. In hot environments or long bursts, heat matters.

Compression, Bit Depth, and the “Free Speed” Settings

Small changes in file size pay big dividends for sustained fps:

• RAW compression:
• Lossless compressed: Typically 20–50% smaller than uncompressed, little to no quality impact.
• High‑efficiency RAW (brand‑specific): Can be even smaller; check your workflow compatibility.
• Bit depth:
• Some cameras reduce bit depth (14‑bit → 12‑bit) for top fps modes; that reduces data rate.
• File type:
• RAW+JPEG vs RAW only: If you must shoot both, consider smaller JPEGs or only RAW during action sequences.
• Flicker reduction & anti‑flicker:
• Can reduce maximum fps on some bodies. If you’re chasing max bursts under artificial light, test the impact.

How to Test Your Real-World Throughput at Home

You don’t need lab gear to validate performance. Try this:

• Update firmware for camera and card if applicable.
• Format the card in-camera.
• Set RAW type and burst speed as you plan to use.
• Point at a scene with real detail (avoid blank walls; compression will skew results).
• Hold the shutter until the buffer indicator shows you’re in the “sustained” state.
• Keep shooting for a timed 10 seconds.
• Count frames captured during those 10 seconds (use file numbering).
• Offload and note average file size for those frames.
• Compute sustained write: frames × avg MB / seconds

Example: 90 frames × 45 MB / 10 s = 405 MB/s sustained.

Repeat for different cards and settings (e.g., lossless vs uncompressed). This reveals whether your limiting factor is the card or the camera.

Capacity Strategy for Burst Shooters

• Bigger cards often sustain high speeds longer before any internal cache or thermal throttling kicks in.
• For high-MP cameras at fast bursts, capacity drains quickly. Example: 45 MB per RAW at 20 fps is 900 MB every second; even if you don’t sustain that, a sports half can eat tens of gigabytes.
• Consider multiple cards for rotation in hot conditions to keep temperatures in check.

Thermal Management: Keeping CFexpress from Throttling

• Avoid leaving the camera idling in direct sun with the card warming in the slot.
• In long events, rotate cards to let one cool in the shade.
• Some cards include heat spreaders. They can help but expect the camera body to get warm too.
• If your body allows, brief breaks between long bursts can preserve higher sustained rates.

Maintenance That Keeps Cards Fast

• Format in camera before important shoots.
• Periodically perform a deep refresh/secure erase with the manufacturer’s utility (CFexpress) to restore performance, if the vendor recommends it.
• Replace aging cards used heavily for video; sustained write performance can drift over long lifecycles.
• Treat cards like critical gear: cases, dry storage, no bending/pressure, and clean contacts if needed.

Quick Picks by Camera Category

Note: Always confirm slot types for your specific model.

• Pro mirrorless/DSLR with CFexpress Type B (e.g., Nikon Z9/Z8, Canon R3/R5/R6-series variants with CFexpress, Fujifilm X‑H2S, GFX 100 II, various Panasonic S/E bodies):
• Choose a VPG400-capable or “sustained performance” CFexpress Type B from a top series (Cobalt, DIAMOND, AV PRO, BLACK).
• Disable simultaneous recording to SD during action bursts.
• Prefer lossless compressed RAW for longer high‑fps sequences.

• Sony bodies with CFexpress Type A (A1, A7R V, A9 III, newer Alpha lines with Type A slots):
• Pick premium Type A cards focused on sustained write and thermals (Sony TOUGH, ProGrade Cobalt, Delkin BLACK).
• Expect excellent burst performance, but not Type B levels; manage expectations for 30 fps RAW beyond buffer.

• SD‑only cameras (e.g., many midrange mirrorless/DSLR, OM System/older bodies, X‑T line):
• Buy V90 UHS‑II from a reputable pro series; avoid V30/V60 for heavy RAW bursts.
• Test lossless compressed RAW and 12‑bit options to extend bursts.
• Consider using a single slot for RAW (no backup) during critical action.

Workflow Note: Readers and Offload

This doesn’t affect shooting speed but matters for sanity:

• Use a reader that matches the card tech (CFexpress Type B reader, UHS‑II SD reader).
• Connect via fast USB (10 Gbps or better) or Thunderbolt.
• Slow readers turn big bursts into long waits.

Troubleshooting Checklist: Sudden Slowdowns

• Did you switch to uncompressed RAW?
• Is anti‑flicker/flicker reduction enabled?
• Are you writing to both slots?
• Is the card nearly full or very hot?
• Is this a new card without firmware updates?
• Did you format in camera?

FAQ

Q: Do I need CFexpress for RAW bursts, or will UHS‑II SD work?

A: It depends on your camera and fps target. For sustained 10–15 fps with high‑MP RAW, CFexpress Type B is often required. For moderate fps or lower MP bodies, a top-tier UHS‑II V90 card can be enough, but you’ll rely more on buffer.

Q: Are “V90” and “VPG400” the same?

A: No. V90 is an SD minimum sustained write class of 90 MB/s. VPG400 is a CFexpress certification guaranteeing ≥400 MB/s sustained write. Both are useful, but they apply to different card families.

Q: My card advertises 300 MB/s, why is my burst still slow?

A: That’s usually a peak read speed. Write speed is lower, and sustained write can be much lower. Also, your camera’s controller may cap write speeds. Look for sustained write specs and real‑world tests, not just the biggest number on the label.

Q: Is CFexpress 4.0 faster in my current camera?

A: Only if your camera supports the faster interface. Most current bodies use Gen3 controllers. CFexpress 4.0 cards are backward compatible, but you might not see a speed increase.

Q: Should I shoot RAW+JPEG for sports?

A: If you’re chasing max sustained fps, shoot RAW only to the fastest slot. RAW+JPEG increases write volume and can drop your post‑buffer fps.

Conclusion

If you care about long RAW bursts, your memory card isn’t an accessory, it’s the throttle. Match the card to your camera’s slot type, aim for sustained performance (VPG400 for CFexpress, V90 for SD), and set up your camera to minimize data per frame. Test your real-world throughput, keep firmware current, and manage heat during long shoots. Do those things, and your camera will spend more time at full stride and less time gasping against the buffer.

Next steps:

• Verify your slot type(s) and update firmware.
• Choose a card line known for sustained writes (not just peak).
• Set lossless compressed RAW and single‑slot recording for action.
• Run the 10‑second sustained test and lock in a card you trust.

That’s how you turn the promise of high fps into reality, frame after frame, when it counts.

Try my preferred memory card brand, ProGrade Digital.

You May Also Like

Master the New Color Mixer Tool in Lightroom Classic for Perfect Color Adjustments

October 11, 2023

HDR Express announced from Unified Color, simple HDR software

October 28, 2010

Photo Found – The Amber Jets

January 13, 2009