Firstly, I have not had an interest in flash photography. But, this shot has me wondering how the camera bodies processors determine flash intensity and timing. Using flash in your photography, do you have full control of timing, duration and intensity?
Not exactly, we don't have to worry with timing or duration. But yes, we do have full control over the flash output power (intensity, or exposure), which is surely all that matters.
If using Manual flash mode, we simply just set any power level we desire. 1/2 power, 1/8 power, whatever. A little experience easily puts us into the right ballpark (will be about like last time in a similar situation). When and if we see that is too much or too little power, we simply adjust it (in 1/3 stop steps), and shoot again.
If using TTL flash mode (automatic point&shoot flash), the camera meters an automatic preflash, and determines what the power level should be. Again, if we see that is a little too much or too little, we use the Flash Compensation feature to adjust TTL, like +0.3 EV more exposure, or -0.6 EV less, etc... And then shoot again. This is adjusting the cameras metering goal (for that subject situation).
The camera meter is necessarily a reflective meter, all of which are influenced by the subject and/or background colors. Highly reflective colors (like white) read high (and are underexposed a bit), and low reflectance colors (like black) read low (and are overexposed a bit). The camera always tries for a middle tone average, not knowing what the subject is, or how it ought to be.
Mid-tone average is often about right for an 'average' subject, like a landscape containing a mix of colors.
But more localized subjects, maybe not always precise, until we adjust it.
This is true of any camera meter reading, sunlight too, and is Not different for TTL flash, so it is nothing new, but flash is not exempt either. So when and if not quite satisfactory, we simply compensate it a bit, until it is.
We could instead use a hand held incident meter, metered from the subjects position (aimed towards camera) to instead meter the actual light (at the subject), which is then independent of the subjects reflection. It will be about dead on correct, every time.
But after you've done a couple of shots like yours, and we can recognize the white or dark background, so we simply just already know that about the same thing next time will be about the same flash situation, for either manual or TTL flash. Not difficult at all, but yes, we do have to use our heads a bit.
