Quality of light comparison #3

[john_murphy1]

Here is another quality of light comparision for informational

purposes.</p>

This demonstrates the effect of the distance between the main

light and the subject. I used a 3ft wide softbox at three different

positions. Otherwise, the setup was identical for each shot.</p>

You can see that at distances less than the diagonal width of the

softbox, it produces softlight, but as you pull it further away, the

light gets harder and the contrast increases.<div></div>

[emre]

Very useful! You should do another test with softboxes of different size, if possible. Also note that the catchlight is more visible when the softboxes is placed further away.

[eddie g]

John, I really appreciate you taking the initiative to help us newbies. This is a great post with a very useful illustration/example. Members like you make photo.net valuable.

 

Eddie

[timcorridan]

yes thank you, i prefer the middle one, 3' away.

[manolis1]

John Murphy I want to thank you as well. BTW I like the first one.

[john_murphy1]

The purpose of this is to demonstrate that a softbox's "softness" varies with the light's distance from the subject. At some point, the softbox stops acting like a softbox and starts acting like a regular reflector.</p>

 

If you've ever taken readings with your lightmeter at progressively longer distances from the softbox then you've no doubt noticed that the light doesn't falloff much when you're up close to the face of the softbox. But as you get further out, suddenly the falloff becomes more rapid, that is, it follows the inverse square law.</p>

 

This is because the softbox acts like an infinite plane source when you're close to it, but it acts like a point source as you get beyond a certain point. An ideal plane source has no light falloff as you move further away from it. A point source of light obeys the inverse square law, that is, the intensity of the light decreases by a factor of four each time you double the distance. How far out you have to go before you start to see this change varies with the geometry of the softbox.</p>

 

The math behind this is probably more than most of us would like to tackle. <a href="http://en.wikipedia.org/wiki/Intensity">Here</a> is a link to the applicable formula if you want to attempt it.</p>

 

Suffice to say that if you stay within a distance equal to or less than the diagonal width of the softbox you'll be okay.

[John G.]

I know that this thread is moving down the page, but I thought I'd add my 2cent opinion:

 

The concept that backing a light out makes it contrastier is wrong and not an appropriate approach to lighting. At least in the type of photography I do.

 

Truthfully, moving the light closer to the subject makes it contrastier or more 'specular', although the shadow edge transfer gets softer. Images aren't seen as shadows, but as light.

 

 

The realities on a multilight set, with a variety of equipment is that overall contrast, and to a lesser extent, the apparent size of the light source is controllable through fill. The local contrast on the skin can be measured in terms of specularity.

Look at lighting in terms of it's inherent contrast (amount of diffusion), size, and specularity.

 

Look at the posted images, and agree or disagree by deciding for yourself if you think that the first image is contrastier than the last. Things get more complex as lights are added.

 

My two cents, and minor pet peeve.