Posted on May 17, 2011 | Comments 0
Photography is an art. This fact is undeniable. Nonetheless the artists might be faced with the situation when they have to learn a little something about sciences like physics. There are numerous laws of physics that are used in photography, and one of them is the inverse square law.
The name of the law doesn’t really mean anything to those who don’t know what it refers to. The principles of this law take effect especially in case of studio lights or flash. According to this law, an object that is located twice the distance from a light source will receive only a quarter of the illumination.
Simply put, this means that in case you move an object from three meters to six meters from the light source, you will need light that is four times stronger in order to have the same exposure.
To achieve this you could open the lens aperture two f-stops or you could use a flashgun that is more powerful.
In this case the light source might be any lamp or flashgun that the photographer uses. It is important to remember that the effects of the law apply only to the unfocused light sources.
In case of highly focused point source, like a laser, the light won’t drop off so fast.
The main reason for which the power of the light source diminishes is that it spreads. This way a smaller amount of light hits the object in question.
In case everything is automatic on your camera and you use the flash, you don’t really have to worry about this law. The only problem is that your flash might turn out to be not strong for objects found at a greater distance.
The inverse square law is to blame for the difference in exposure time regarding the objects that are found near the camera and those that are further away.
Some of the photographers consider that it is a sin to have a flash on the camera and that the flash should be used only in case there is no other alternative. In case of the flash you don’t have any control on the distance between the light source and the object itself. In many cases the professionals choose to have the light source closer to the object than the camera.
They do so because this way the object will have more light, and the other reason is that the shadows on the object will be softer.
The automated cameras will do the math for you and you won’t have to worry about such things. Nonetheless, you should know what is really going on in the camera, so it won’t come as a surprise to you that the picture you just took is overexposed. Remember that this is an effect of the inverse square law, and you can fight it by means of light.
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