U were saying something about the flashing knows how much light to add but doesnt know how much reflected back ??...
what does it mean ???...
I mean, you take a picture of a piece of black paper and you then take a picture of a white piece of paper. The white paper will reflect much more light back towards the camera. The same thing happens with anything in your shot, lots of light wall covering (paint/paper) or light vs dark clothes, a white wedding dress will usually bounce more light than a black dinner suit.
The other thing is you say you were in full manual mode which means you didn't allow the camera to use it's TTL metering to adjust certain settings.
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