Why does my Canon R6/R5 show a dark band at the bottom when I use a flash?

Have you ever mounted a flash to your Canon R6 or R5 (both Mark I and Mark II versions)? You may have seen a dark bar creeping across part of your frame. Let’s dive into why this happens and how to prevent it.

Understanding Flash Sync Issues on Canon R6 and R5

When you use a full-frame flash with Canon R-series cameras, the maximum shutter speed allowed for full flash coverage is:

• 1/200 s using the mechanical shutter.

• 1/250 s with Electronic First-Curtain Shutter (EFCS).

  
  

When you exceed these speeds, the rear curtain starts to close before the flash fires. This leads to only a narrow “slit” of the sensor being exposed to light, causing the rest of the image to remain dark.

This limitation is known as X-Sync. Basically, X-Sync is the fastest shutter speed where your camera’s two curtains fully expose the sensor simultaneously. If you fire the flash too quickly, part of the frame stays covered by the second curtain during the flash burst.

Top Tip:

Always check your X-Sync before you shoot. Even if you don’t intend to push to 1/250 s, it's wise to be aware of your camera’s flash limits. To avoid surprises, stay at or below the sync speed, or activate HSS if you need to shoot faster.

How to Shoot Faster without the Black Band in Your Photos

Use High-Speed Sync (HSS)

• What you get: The flash emits rapid pulses at lower power across the entire exposure, “painting” light as the shutter slit travels.

• How to enable:

1. On an HSS-capable speedlight, find the ⚡ ＋ H icon and enable it.

2. On your R6/R5, navigate to:

- Shooting Menu → External Speedlite Control → Flash Function Settings → Shutter Synchronisation → High-speed synchronisation.

• Trade-off: Expect a reduction of about 2–4 stops in effective flash output.

  
  

Utilize ND Filters

Fitting an ND filter can help you reduce ambient light. This allows you to maintain a shutter speed at or below 1/200 s, even in bright conditions. You can also keep a wide aperture for beautiful background blur.

Specialty Lenses with In-Lens Shutters

Specialty lenses often come equipped with in-lens shutters that can sync at incredibly high speeds (typically 1/1,000 s and above). Though they might be pricier and less common, they provide full flash power at any shutter speed.

Continuous Lights and Powerful LED Panels

Powerful LED panels or studio heads function continuously, so they don't rely on sync speeds. This means you can shoot at any shutter speed. However, be mindful longer exposures can lead to motion blur.

Flashes at Different Price Points that Do Support HSS

Tier	Model (Canon-mount)	Approx. UK Price	Key HSS Feature
Budget	Godox TT685II-C	from £80	1/8 000 s HSS, built-in 2.4 GHz radio “X” system
Mid-range	Godox V860III-C	~£175	Li-ion pack, 1/8 000 s HSS, rapid recycle & radio control
Premium	Canon Speedlite 600EX II-RT	~£426	Full E-TTL II, 1/8 000 s HSS, master/slave radio, GN 60

Top Tip: Keep both your camera and flash firmware current. Manufacturers frequently enhance HSS timing and performance through updates.

Frequently Asked Questions

Does using HSS drain battery life faster?

Yes, continuous pulsing during exposures increases recycle times, thus draining the batteries quicker. To alleviate this, consider using a Li-ion pack (e.g., on the V860III or Canon EL-1).

Can I use HSS with a mirrorless camera?

No. In HSS mode, the sensor reads line-by-line, meaning the full frame is not presented to any single flash burst. This results in either no flash or heavy banding. Stick with the mechanical shutter or EFCS for strobe photography.

How can I avoid clipping at sync limits?

Timing variances or slower-recycling flashes can result in clipped edges at the sync limit. If you drop back one third-stop (e.g., to 1/160 s) or activate HSS, you can ensure full frame coverage.

With these tips, you can confidently use HSS, ND filters, leaf-shutter lenses, or continuous lighting. This knowledge allows you to push your Canon R6/R5 to faster shutter speeds without fearing that annoying dark band.