How do you do that Spotlight/Light Beam effect

Started 4 months ago | Discussions thread
Rico Tudor Contributing Member • Posts: 834
Re: How do you do that Spotlight/Light Beam effect

Of course strictly speaking the inverse square law ONLY applies to the theoretical point light source, but is a good rule of thumb for most photographic light modifiers, but not so good for focused or parallel light.

Laser light is indeed coherent but also collimated—the characteristic required to project a "spotlight" over some distance with sharp edges. Unfortunately, that beam is only pencil wide! Similarly, a theoretical point source could be collimated by a followspot or projector fixture but the beam diameter would equal that of the front element: again, unworkable for human subjects. All lighting instruments for photographic use are very far from providing a point source, and the spotlight effect is created by focussing the optical stop. Inverse square is then applicable in mathematical terms, and demonstrable by simple experimentation. The sun is not a point source, either: shadow edges quickly become fuzzy with distance, and projecting an image of the sun with any lens will obey inverse-square. Try it.

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