Can I see what flash power Canon E-TTL used and match it in manual mode?
Asked 2/9/2011
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2 answers
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When using a Canon Speedlite in E-TTL, is there any way to see what flash output the camera/flash actually chose for a shot? I’d like to know whether that information is shown on the camera, the flash, or stored in EXIF, and whether it varies by Speedlite model.
My goal is to judge how close I am to full flash power. For example, if E-TTL is already using nearly full output, I might raise ISO to leave more headroom. If it’s using very little power, I might lower ISO. I know the flash exposure confirmation light can indicate a successful exposure, but can it tell me how much margin I had?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
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One way to see this is to use manual (M) mode when using a flash.
As you adjust the aperture and shutter speed, the exposure metering will be displayed in the viewfinder. If you are using ETTL, then the flash will make up for the difference between the metered exposure and the "Correct" exposure.
If you know what the difference was you can calculate when settings you should use in manual mode using the flash's Guide Number and the distance to the subject.
I know this isn't truly what you had in mind, but the flash power is not included in the exif data.
Originally by user67. Source · Licensed CC BY-SA 4.0
user67
15y ago
0
Generated from our catalog & community — verify before relying on it.
Generally, no: Canon E-TTL does not give you a direct readout of the exact flash power used, and that value is typically not recorded in EXIF. So you usually can’t take an E-TTL exposure and simply switch to the exact same output in manual mode.
What you can do instead:
- Use experience and guide numbers to estimate a manual starting power based on distance, aperture, and ISO.
- In camera manual exposure mode, watch the ambient meter separately; E-TTL will then add flash to reach its target, but this still won’t show the exact fraction of full power used.
- Judge headroom roughly by flash recycle time: if recharge takes nearly as long as it does after a full-power manual pop, you were probably near full power. If it’s almost instantly ready, output was low.
- The flash exposure confirmation light only tells you the flash had enough power for that exposure; it does not indicate how much reserve remained.
If you need exact flash measurement, a dedicated flash meter is the better tool.
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