OK so I admit that as a newbie non-professional photographer, there's one thing that's been bugging me & I can't quite get my head around it. Unfortunately, I'm the sort of fellow who has to know why things are a certain way; I'm not satisfied with rote learning.

OK so we all know that if you use a reflection lightmeter settings to photograph a white cat in snow, or a black dog in coal, you'll end up with gray cats in gray snow and gray dogs in gray coal. That's because of the old 18% dull gray standard (and lets not get into the debate of 16% vs 18%)

In other words, the lightmeter is just a photoelectric cell, whose readings have been calibtrated so that it will convert the amount of light present into aperture/shutter speed settings that will result in 18% dull gray images.

This applies to reflection lightmeters - light meters that read the amount of light that is reflected off of the subject. And that's why the Zone System adjustments are necessary etc etc.

This does not apply to incident light meters - light meters that measure the amount of light falling on the subject.

So here's my question: why the difference between incident v. reflected light meters? Whether the light they're reading is reflected or incident, all lightmeters still have to have to be calibrated, and the calibration of both types is set to result in 18% gray images. If you use a reflected lightmeter to take readings off of a white cat in white snow, that should be pretty much the same as measuring the light falling on it, right?

SOmeone take me through the mental steps!