Why does my off-camera flash underexpose with a wireless trigger in HSS?
Asked 8/14/2020
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2 answers
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I’m using a Fuji X-H1 with a Flashpoint R2 Pro II transmitter and a TT350 flash. If the TT350 is mounted directly on the camera, it exposes normally at 1/2000s, f/4.5, ISO 100, and 1/16 power in HSS. But when I remove the flash from the camera and trigger it wirelessly with the R2 Pro II, the images become much darker even though the flash is still set to 1/16 power.
What could cause the flash to lose so much output only when used off-camera with the transmitter?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
1
It looks to me like the flash is pointed straight at the mirror when attached to your camera and may be pointed up at an angle when you are holding it in your hand.
Rather than trying to compare flash brightness by a reflection in a mirror that is very sensitive to the angle of the flash's beam, have you tried using it to illuminate a subject that does not include the flash itself?
Another thing you might want to look at is the focal length of the lens you are using versus the "Auto" setting on the flash (when attached directly to the hot shoe) versus "70mm" when controlled by the R2.
Is the lens you are using a 70mm lens? A 45-50mm lens? Something else? Flash zoom settings should be adjusted to "equivalent focal length" because the critical thing is actually angle of view, not focal length. Flash zoom setting affects the size of the cone of light projected by the lens, which in turn affects the density of light per unit area.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
5y ago
0
Generated from our catalog & community — verify before relying on it.
A few likely causes are suggested by your test setup.
First, at 1/2000s you’re in HSS, and off-camera HSS is more demanding than on-camera use. Some trigger/flash combinations may not deliver the same effective output remotely, or may become unreliable at very fast shutter speeds. A good test is to try a darker room and lower shutter speeds first, then increase the shutter speed until the problem appears.
Second, compare the flash zoom setting. On-camera the flash may be using Auto zoom, but with the trigger it may be fixed to 70mm. That changes beam spread and can make your test look darker depending on distance, framing, and subject.
Third, don’t judge brightness from a mirror reflection. Small changes in flash angle can greatly change how bright the reflection looks. Test on a normal subject instead, keeping distance, angle, and zoom consistent.
So the most likely explanation is a combination of HSS limitations off-camera plus different flash zoom/aiming rather than the flash power setting alone.
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