How can I keep direct flash from overpowering a night scene without lots of trial and error?
Asked 7/29/2015
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I understand the basics of flash exposure compensation and balancing flash with ambient light. What I want is a practical guideline for estimating a good flash-to-ambient balance more quickly, instead of testing many shutter speeds.
For example, when photographing my garden at night with my Sony NEX-5R and its direct on-camera flash, one flash shot looked obviously overpowered, while a much longer shutter speed gave a better result by letting the ambient exposure build up.
I don’t have off-camera flash, modifiers, or a tilting/swiveling flash head. My main control is the balance between flash and ambient light. Is there a rule of thumb—similar to Sunny 16—for choosing flash power or settings so the flash fills the foreground without looking artificial?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
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The duration of the flash is much shorter than any of the shutter speeds you are using, so the shutter speed doesn't directly affect the amount of light from the flash that winds up in the scene. What does seem to be happening here is that the camera is treating the flash as fill light and automatically adjusting the flash power to balance with the amount of ambient light, which is affected by your selected shutter speed. If you don't have a way to manually control the flash power directly then pretty much all of the standard "rules of thumb" go out the window - your camera will alter the power to counteract most of what you do. At least it will until you close the aperture and reduce the ISO to the point where the flash is at full power so the camera can't add any more to compensate for allowing less ambient light into the frame.
In addition to flash exposure compensation, you can also dial in regular exposure compensation. This will reduce the amount of total light (ambient light + flash light) that the camera thinks it needs to get a well exposed shot.
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
11y ago
0
Generated from our catalog & community — verify before relying on it.
There isn’t a simple “Sunny 16 for flash,” especially if the camera is controlling flash output automatically. With direct flash, two useful principles apply:
- Shutter speed mainly affects ambient light, not flash exposure. The flash burst is much shorter than your 0.8s–30s exposures, so longer shutter speeds brighten the background/ambient portion of the image.
- Flash power for manual direct flash is estimated with the Guide Number (GN). GN gives a starting point for aperture and distance at a given ISO, but it applies best in manual flash mode.
If your camera/flash is using TTL or automatic fill flash, it may change flash power as you change shutter speed, which makes rules of thumb less reliable.
So the practical approach is:
- Use shutter speed to raise or lower the ambient scene brightness.
- Use flash compensation or manual flash power (if available) to control the foreground fill.
- If possible, lower ISO or stop down aperture when the flash is too strong.
- For manual flash, use the flash’s guide number chart as your starting estimate.
In short: GN is the closest thing to a flash rule of thumb, but with automatic flash, some testing is still unavoidable.
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