Lighting 102: Side Effects
Every change you make to a light source has an obvious, primary effect. But it also has less obvious, secondary effects. Much like opening up your aperture lets in more light, but it also reduces depth of field.
If you also wanted reduced depth of field, that's a good thing. But if you do not want that, you should instead open up your shutter speed or increase your ISO. You get the point.
Moving a Light Closer
• Increases exposure value of light falling on subject.
• Decreases the "depth of field" of the light. I.e., the light falls off more quickly as the light continues to travel past the subject.
• Increases the apparent size (and thus the softness) of the light.
• Moving a light further back has the opposite effects.
Increasing the Size of a Light Source
• Increases the softness of a light source.
• Makes specular highlights bigger.
• Makes specular highlights less intense per square inch (same total amount of light, from a bigger light source.)
• Decreasing size of a light source has the opposite effects.
Remember, you can also adjust the amount of light falling on your subject by changing the power level of your flash.
Increasing the Power of a Light Source
• Will add light to your subject, all other things being equal.
• Will increase recycle time, which can be a factor in your shooting rhythm as you approach full power—especially when using speedlights.
• Decreasing power to the light source has the opposite effects.
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