Using inverse square law in photography

[k.udhay]

Hi,

I recently went through the video of using inverse square law in photography in the following link:


I am quite clear about the concept except for two things:

1. When he explains us the inverse square law in photography with the subject including a background, he shows us how bright / dark the background becomes (at time 08:35). What is not so easy for me to understand is, the background which is at the same distance from the light source changes its brightness as the subject moves. Why does the background become more existing when the subject moves close to the background?
2. In case I am capturing photos out of studio, like some natural scenes, though the mountains are far away from the camera and light source, why don't they become dark?

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Pl. help me to understand this. I think I can get some dark backgrounded photos if I use this concept correctly. Thanks.

 

[pgriz]

Natural scenes are lit by the sun, and at the distance the sun is from Earth, we are all effectively at the same distance from THAT light source. As for the studio shot, the background is getting the same illumination. But the subject is moving closer or farther from the light source, and the photographer is adjusting the exposure for the subject, not the background. If he didn't, and had the exposure dialed in for the background, the subject would be overexposed when closer to the light, and underexposed when further from the light.

 

[k.udhay]

Thanks pgriz...