Why does light get harder with distance?

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Duncan.F

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This came up on a recent course and I don't understand it. Light falls off with the inverse square rule, I understand that. But how does light from a flash become harder the further away it is...?

Dunc
 
because the light source (from the viewpoint of the subject) gets smaller
 
Ok but doesn't it follow that it also becomes more diffuse? If I point a bright torch at something 2 feet away I get an intense circle of light. If I move away say several yards the light from the torch spreads out and becomes softer.....?
 
Duncan.F said:
I am not sure! It was a term that was used several times and I didn't understand it1
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hard light just means from the subjects perspective that light is from a small source, regardless of power, so a bare flash head is normally a hard source.
 
boyfalldown said:
hard light just means from the subjects perspective that light is from a small source, regardless of power, so a bare flash head is normally a hard source.
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x2.

The larger the source of the light, the softer the effect, this is why bouncing off the ceiling is used a lot, because the ceiling is a reflective surface, you get a wider range of light.
 
You understand the reason for diffusers yes?

Combine that with what the others have said, think about it and you have the answer (as they are really just extremes of the same situation).
 
The bit you're missing is that the subject doesn't become any different with size the further away it is. The light rays are emitted in a straight line, so the further away the subject is, the smaller an area it gets lit from the light. Think of a star - absolutely huge justa long way away so only seen as a very hard point of light.
 
itsdavedotnet said:
because the light source (from the viewpoint of the subject) gets smaller
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That's a good answer in practical terms. Dave says that it gets smaller from the viewpoint of the subject - think of it in terms of getting smaller in relative terms, i.e. that it gets smaller relative to the subject. It might help, because light gets harder when it gets smaller in relative terms.

Think it terms a large light source such as a softbox that is twice as wide as the subject.
Now, that large light source will light the subject from various different angles, it will light it from the middle, going straight to the subject, it will light it from each end, lighting the sides of the subject to some extent (often referred to as wrap around lighting) and it will light it from every intermediate point too. Each tiny point from that softbox (lighting source) will be its own lighting source and will create its own light. therefore each tiny point will create its own shadow, and those shadows cross over each other and soften all the other shadows created by the other point sources of light. As you move the light further an further away, the point sources of light get closer and closer together in practical terms and eventually, if you move the light far enough away, all of those millions of point sources become almost a single point source, creating a single shadow instead of a complex set of shadows.

Example: The sun. It's massively bigger than the earth but because it's also 93,000,000 miles away it looks small. On a clear day with no clouds it becomes a small light source in practical terms and so casts a single hard shadow. On a cloudy day, when you can't see the sun, the whole sky becomes the light source and is similar to a very big softbox, the light is coming from so many different directions that all the shadows overlap and merge and you can't see any shadows.

There's a lot more to it than that, but hopefully it helps, without getting complicated.
 
Ok, i think i know what you are talking about, but correct me if i am wrong.

Senario i think your getting at is this.

Camera is set at point a, which is 50 feet from end of the subject line (wall) subject is at 40 feet, (10 feet from wall) Light on the background will be "hard" as the subject is closest to the end line.

If subject is at 10 feet, (40 feet from wall) light will be softer as the subject if further away from the end line.

Light rays are incoherant, flash, buld, torch, there are all incoherant so they do not radiate in a straight line from the source, (laser light is coherant light)

Light from a star, (defination of star is our sun) is bright and seems like a single point, because the light is being emitted from the entire source.

If you stand 1 mile away from someone else with a powerfull torch, you would get a star effect, but the light rays over that distance would not show on you, becuase of the way the incoherant light has become diffused over distance.
 
You are overcomplicating this?

If the light source is relatively large compared to the subject, light rays will be hitting the subject from many angles - imagine replacing the softbox with a 100 x 100 array of small point lights. Then expand that thought to infinite x infinite array... Not all of these imaginary point lights will be illuminating every part of the subject, thus resulting in soft shadows.

Now if the light source is relatively small, all the light rays will be coming from single or very restrict arc of angles, thus creating harsh light - everything is either lit or not lit.
 
vaizki said:
You are overcomplicating this?

If the light source is relatively large compared to the subject, light rays will be hitting the subject from many angles - imagine replacing the softbox with a 100 x 100 array of small point lights. Then expand that thought to infinite x infinite array... Not all of these imaginary point lights will be illuminating every part of the subject, thus resulting in soft shadows.

Now if the light source is relatively small, all the light rays will be coming from single or very restrict arc of angles, thus creating harsh light - everything is either lit or not lit.
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You forgot distance.
 
Well distance changes the relative size of the light, that was the whole point.. but you're right, I should've slipped the words in there ;) But I think Dunc got it now so I was late anyway..
 
Yes it'a all about the relaite size of the light source in comparison to the subject. A small subject may require a small light source to provide a soft light but for a person it will require much larger and ideally closer.

With a large source of light the light also wraps around the subject. It's this wrap that provides the soft effect.
 
Duncan.F said:
Ok but doesn't it follow that it also becomes more diffuse? If I point a bright torch at something 2 feet away I get an intense circle of light. If I move away say several yards the light from the torch spreads out and becomes softer.....?
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In addition to the replies above, this bit is wrong: "If I move away say several yards the light from the torch spreads out and becomes softer.....?"

No, it becomes dimmer and also harder (because it is smaller relative to the subject) but because it is so small to start with you won't notice much there.

If it was a big softbox, then the light would get rapidly both much dimmer and harder.
 
Think of the sun on a cloudless day.

Shadows are sharply defined and "hard."

Now think of an overcast sky - the sun is still there but the shadows are now softer and diffused.

Almost the same effect as a flash and diffuser.

.
 
Thank you all again! So many different explanations and I loved the father Ted one!

Cheers,

Dunc
 
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