Ley De Inverso - Fotografia (Ingles)

The Inverse Square Law - what it means to Photographers
It's useful to know a little about the inverse square law especially when using flash or studio lights. Basically all the inverse squarelaw says is that an object that is twice the distance from a point source of light will receive a quarter of the illumination. So what it means to us photographers is that if you move your subject from 3meters away to six meters away, you will need four times the amount of light for the same exposure. This can most easily be achieved by opening the lens aperture two f-stops (see aperture for anexplanation) or using a flashgun that is four times as powerful.
What do we mean by a point source of light? Well in Physics there might be a very strict definition but for our purposes any flashgun or lampcan be considered a point source. The other variable to be aware of is that the law works for 'unfocused' light sources. Light from a laser or other highly focused source will not drop off quite sorapidly.

The more the beam is focused the higher proportion of the light will fall on the object. With a theatrical spotlight for instance which has a very narrow beam, much more light will fall onthe object.
In photography though we don't tend to use highly focused beams as they produce a very harsh light, too contrasty for our purposes. So the inverse square law, as a rule of thumb, worksvery well for us.
So why do we need to know this?
If you are using flash on camera and everything is automatic then you don't need to worry about it at all. Except you may 'run out of light' becauseyour flashgun is not powerful enough. It also explains the big difference in exposure between objects or people near the camera and those only a few feet further away.
If you have read my tutorialon flash photography though you will know that I consider 'flash on camera' as one of the cardinal sins of photography, and should only be used in extreme emergencies. If your flash, or light source,...