Very Interesting Gary and a great demonstration of the effects.
Can you just clarify a couple of things for a novice like me, you talk about wrap arround "
The larger the softbox (or other light source) and the closer it is to the subject, the greater the wraparound effect, and once it’s has been moved to about the diagonal measurement of its front surface (which in this case is about 85cm), it lost its wraparound effect and in effect stops behaving like a softbox."
OK I thought that wrap around meant that more of the subject would be lit, lightening the shadows. I note from your test shots when the light was close the shadows were darker and covered more of the cheek and the edges were more defined. As the light gets further away the shadows get lighter and less of the cheek is in shadow and the edges of the shadow more gradual. Therefore at a greater distance (in my mind) the light is wrapped around more. Which would contradict the quoted statement above, so what am I missing here?
Softboxes soften the light...right? So when you say "
stops behaving like a softbox" in the above statement what do you mean, what else should we expect from a softbox? Because to my eye the shots from greater distance look softer. So I thought it acted more like a softbox when it was further away? again am I missing something?
B.T.W. I know what Im doing at the weekend now
I know what I'm doing at the weekend too - and it isn't photography
Two different things here...
Wraparound occurs when the light source is larger than the subject.
The front of the subject is lit by the central area of the light source, say the softbox.
The sides of it are lit too, by the edge areas of the softbox. It isn't the same intensity of light at the edges because the light from the edge areas has to travel further, and the inverse square law (which says that a point source of radiated energy (light, heat, noise etc) loses its power to the square of the distance, so if the light that reaches the sides of the subject from the edges of the light source has to travel twice as far, 75% of the light has been lost.
Because of the way that light falls off over distance, the shots taken with the softbox really close to the subject have more obvious modelling than the ones with it further away - there is more obvious difference between the amount of light hitting the forehead than the chin. The light is in fact much softer, perhaps you are confusing eveness of lighting with softness.
But, the inverse square law doesn't just affect the delivery of energy. If you move the light twice as far away, in effect it becomes just 1/4 of the size. An obvious illustration of this is the sun, although the sun is 100 times bigger than the earth, it is also 93,000,000 miles away and so looks smaller when viewed from the earth, and the light it casts is very harsh because of this. In effect, it doesn't matter that the sun is so large, it is small in relative terms so the light is harsh and there is no wraparound effect. But, make that light larger, which it is on a dull day when it is totally obscured by cloud, and the whole sky becomes one massive light source, with the result that the light is extremely soft, with no shadows, and with a very pronounced wraparound effect.
So, if you move the softbox further away, it becomes smaller in relative terms and loses its ability to behave like a softbox, it loses its wraparound effect. If you moved it 1 mile away it would just be a pinprick of light.
All this is in fact explained in the tutorial
