Hi Asher,
Asher Kelman said:
Sean, I have a rather basic nomenclature question. Why don't we express exposure as a simple factor like
E 0.33 and FE 0.67, total =1.0
0r else 33% ambient, 67% total 100%
The practical answer is that we can dial in FEC and EC on camera. So talking about the camera settings is more practical even if it is less obvious/intuitive.
Asher Kelman said:
This would allow easier imagination of how light is distributed.
I agree with this pedagologically, but again at the end of the day we have to deal with decades of ingrained practice/tradition from the camera manufacturers.
Why has no one released an
expose to the right metering pattern? It would be helpful for serious shooters who do post work. Practically, it means if the average consumer grabs a camera in the metering mode they will get lots of overexposed (soft light) and underexposed (hard light) images that cannot be printed directly due to a need for post processing (though it would be cool to see this integrated with RAW and JPEG to do this implicitly behind the scenes). But again, it would change standardized behavior.
Asher Kelman said:
Anyway, how do you cary this math in different circumstances. In external flash we allocate power by Watt seconds or percent. Why not with the camera?
This will not work in practice because Watt-Seconds are not a valid unit for measuring light. The problem here is that this unit of optical prowess must be run through lighting modifiers of some sort (even bare bulb usage shapes the light) and the distance of the subject from the light source affects both the reflected and incident light on the subject. Whereas incident and reflected measures of EV are consistent regardless of the light source. So by measuring the EV we integrate* away a layer of complexity. Hence, one simply dials in a flash EV measure and does not deal with factoring in the the light distribution of a light source (this term integrates away light modifier size, efficiency, the light distribution at the source), the light sources intensity/power/..., and the light sources distance from the subject which would then need to be combined (integrated) to get a prediction. Or we can simply ignore it and measure the EV from the camera viewpoint (reflected metering) or from the subject location (incident metering). And the EV is what we use for calculating exposure (which is greatly simplified using stops/EV/base 2 logarithm).
some thoughts,
Sean <smile>
* To
integrate something is to add it together and create a summary measure of what is dealt with that obscures underlying detail and illustrates aggregate behavior. Or in mathematical terms to integrate over something is simply to add it up.
