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FORUMS General Gear Talk Flash and Studio Lighting 
Thread started 22 Feb 2009 (Sunday) 22:35
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Why Softboxes have to be close to Subject

 
Jamesino
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Feb 22, 2009 22:35 |  #1

In portraiture, why should the softbox be mounted as close to the subject as possible? I read that this allows maximum diffusion of light, but intuitively, would the light not diffuse more if it was set up at a farther distance away from the subject?

Does the same principle apply for bounce and shoot-through umbrellas? Should they be placed as close to the subject as possible as well?




  
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mattograph
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Feb 22, 2009 22:38 |  #2

The apparent size of the light source dictates its softness. The larger the light relative to the subject, the softer. So, the closer the softbox is to the subject, the softer the light.

The physics of it is not the complicated, but if you really are interested, then read "light: science and magic" A great book.


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Perry ­ Ge
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Feb 22, 2009 22:40 |  #3

Mattograph is 1000% right. And consider your 'intuition' for just half a second - think about the sun, it's pretty far, but not very diffuse - why? Because it's a small light source relative to the subject ;).

This is also why stuff like omnibounces do jack **** when you're firing the flash directly at something.


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Hermes
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Feb 22, 2009 22:47 |  #4

Jamesino wrote in post #7384614 (external link)
In portraiture, why should the softbox be mounted as close to the subject as possible? I read that this allows maximum diffusion of light, but intuitively, would the light not diffuse more if it was set up at a farther distance away from the subject?

Does the same principle apply for bounce and shoot-through umbrellas? Should they be placed as close to the subject as possible as well?

Softness and coverage are different things. When you talk about 'diffusion' I assume you are referring to the latter which is just one property of diffusion.

The light will be softer the closer the softbox is to the subject. You will get greater coverage by pulling the softbox further back but this will make the light harsher/more directional, and largely kill the softbox effect. This is why it is important to have softboxes that are the right size/shape for their intended application - so they can be used close to the subject and still give proper coverage.




  
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mattograph
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Feb 22, 2009 22:52 |  #5

Hermes wrote in post #7384712 (external link)
Softness and coverage are different things. When you talk about 'diffusion' I assume you are referring to the latter which is just one property of diffusion.

The light will be softer the closer the softbox is to the subject. You will get greater coverage by pulling the softbox further back but this will make the light harsher/more directional, and largely kill the softbox effect. This is why it is important to have softboxes that are the right size/shape for their intended application - so they can be used close to the subject and still give proper coverage.

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Tom ­ Diego
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Feb 23, 2009 01:12 |  #6

mattograph wrote in post #7384636 (external link)
The physics of it is not the complicated, but if you really are interested, then read "light: science and magic" A great book.

I just bought this book and looked through it today. The authors use a term they call "family of angles" to explain reflection and distance from the subject. The closer a large softbox is to the subject, the more oblique the lighting angles become thus softening the edges of the shadows. The farther away, the more parallel the lighting angles become, causing harsher shadows. This is discussed on page 87. A really great book that explains the behavior of light.



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Curtis ­ N
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Feb 23, 2009 15:05 |  #7

Jamesino wrote in post #7384614 (external link)
In portraiture, why should the softbox be mounted as close to the subject as possible? I read that this allows maximum diffusion of light, but intuitively, would the light not diffuse more if it was set up at a farther distance away from the subject?

The amount of "diffusion" doesn't change. Think in terms of apparent size of your light source.

Consider this: The diameter of the sun is 868,000 miles. It is a huge light source. But since it's 93 million miles away, its diameter relative to its distance is quite small. So we consider it an apparently small light source. The harsh shadow edges we encounter on sunny days are the result of this.

The fresnel lens on the head of a flash unit is only about 2 1/2 inches across. But when we use it for macro photography only 3 inches from the subject, it has a very large apparent size and will produce very soft shadows on the subject.


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Jamesino
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Feb 23, 2009 16:03 |  #8

Curtis N wrote in post #7389434 (external link)
The amount of "diffusion" doesn't change. Think in terms of apparent size of your light source.

Consider this: The diameter of the sun is 868,000 miles. It is a huge light source. But since it's 93 million miles away, its diameter relative to its distance is quite small. So we consider it an apparently small light source. The harsh shadow edges we encounter on sunny days are the result of this.

The fresnel lens on the head of a flash unit is only about 2 1/2 inches across. But when we use it for macro photography only 3 inches from the subject, it has a very large apparent size and will produce very soft shadows on the subject.

Does this mean if I tilt my 580 EX downwards and shoot a portraits at a very close distance, the shadows will also be diffused, similar to a beauty dish effect?




  
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Feb 23, 2009 16:25 |  #9

Jamesino wrote in post #7389868 (external link)
Does this mean if I tilt my 580 EX downwards and shoot a portraits at a very close distance, the shadows will also be diffused, similar to a beauty dish effect?

Are you going to be able to shoot portrait photography 3 inches from your subject? :cool:


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polishpunk68
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Feb 23, 2009 16:33 |  #10

Jamesino wrote in post #7389868 (external link)
Does this mean if I tilt my 580 EX downwards and shoot a portraits at a very close distance, the shadows will also be diffused, similar to a beauty dish effect?

Only if you're shooting a portrait of your fingernail :)




  
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nestle
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Feb 23, 2009 16:36 |  #11

Jamesino wrote in post #7389868 (external link)
Does this mean if I tilt my 580 EX downwards and shoot a portraits at a very close distance, the shadows will also be diffused, similar to a beauty dish effect?

Compare the size of a beauty dish light vs. the rectangular face of the 580EX, regardless of how close you put the 580EX, it can't mimic the round and larger "face" of a beauty dish without some type of commercial or DIY modifier. Simply put, the only way you'll get a beauty dish effect using a 580EX is to somehow transform the light produced by the flash unit to make it look like a beauty dish.




  
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lederK
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Feb 23, 2009 17:09 |  #12

Jamesino wrote in post #7389868 (external link)
Does this mean if I tilt my 580 EX downwards and shoot a portraits at a very close distance, the shadows will also be diffused, similar to a beauty dish effect?

Nope. the front lens of your 580 only define "the largest possible" surface source of light. In reality, however, the light from a flash is not intentionally diffused and is ideally more like a point source.

Tracing the outgoing rays of light backwards, you will find an imaginary point source located roughly 5-30 cm behind the Fresnel lens of the flash (for 28-135mm FF coverage).

Now, I have not done the ray tracing myself, nor seen anyone do it, so it may not be a perfect point source, nor exactly at the positions I mentioned, so its all (fairly reasonable) guesstimations. The Fresnel lens is however not the source of light since it refracts light, not diffuse it.


EDIT: Apparently, I'm a moron. Forget about the rambling above. Please. :oops:


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Curtis ­ N
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Feb 23, 2009 17:18 |  #13

For the purpose of my earlier analogy, let's assume there's a piece of toilet paper taped to the flash head.

Sheesh.


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Feb 23, 2009 22:30 |  #14

Curtis N wrote in post #7390388 (external link)
For the purpose of my earlier analogy, let's assume there's a piece of toilet paper taped to the flash head.

Sheesh.

Does the type of TP change the equation? 'Cause I like the Charmin with the aloe lotion in it. It is very soothing. Also, does the type of TP needed vary by the amount of megapixels. I use high quality TP and it works great with my 30D. If I purchased a 1DsMkIII, could I then use John Wayne TP? ;)


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Feb 24, 2009 00:53 |  #15

tmonatr wrote in post #7392827 (external link)
Does the type of TP change the equation? 'Cause I like the Charmin with the aloe lotion in it. It is very soothing. Also, does the type of TP needed vary by the amount of megapixels. I use high quality TP and it works great with my 30D. If I purchased a 1DsMkIII, could I then use John Wayne TP? ;)

quilted? how many ply? safe for septic? scented? colored? double or triple roll?

these are important questions, and we must get to the bottom of this before we can proceed any further.


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Why Softboxes have to be close to Subject
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