A beginners comparison using a shoot thru umbrella...

[Didereaux]

For those new to using a flash with a shoot-thru umbrella here is a simple comparison showing what an umbrella does to the light and shadows at various power levels compared to the same flash shooting bare. Hope this might help someone along the way. Take note of the last shot in the umbrella sequence and notice that it is very nearly the same as the next to the last shot of the bare flash. That shows the one-stop loss the umbrella causes.

 

[KmH]

Note the difference in the shadow cast by using the umbrella.
The shadow edges are soft and diffuse, and the shadow is not as dense.

The shadow edges cast by the bare flash are sharp and the shadow is much darker (more density).

The bigger a light modifier is, the softer and more diffuse the shadow edges are, and the less dense the shadow is.

 

[Braineack]

top: terry richardson
bottom: annie leibovitz

 

[Scatterbrained]

For those new to using a flash with a shoot-thru umbrella here is a simple comparison showing what an umbrella does to the light and shadows at various power levels compared to the same flash shooting bare. Hope this might help someone along the way. Take note of the last shot in the umbrella sequence and notice that it is very nearly the same as the next to the last shot of the bare flash. That shows the one-stop loss the umbrella causes.

The power level is irrelevant to the quality of light, what matters is the size of the light. I've seen tons of people get caught up in that; thinking that they can get softer light, or more rapid fall off, if they adjust the power of the light. Adjusting the power of the light changes the exposure value, but not the light quality.

 

[Didereaux]

[/QUOTE]The power level is irrelevant to the quality of light, what matters is the size of the light. I've seen tons of people get caught up in that; thinking that they can get softer light, or more rapid fall off, if they adjust the power of the light. Adjusting the power of the light changes the exposure value, but not the light quality.[/QUOTE]


That is correct, Which I think this sequence shows pretty clearly. I personnally don't like to use 'quality' in that context though. The umbrella/diffuser does change the quality of the light from harsh to soft. Quality is a subjective measure in my mind. the diffuser does change the directionality of the light though, To use it as synonymous with the physical aspects seems confusing to me. But that is a very personal opinion.

 

[Scatterbrained]

The power level is irrelevant to the quality of light, what matters is the size of the light. I've seen tons of people get caught up in that; thinking that they can get softer light, or more rapid fall off, if they adjust the power of the light. Adjusting the power of the light changes the exposure value, but not the light quality.

That is correct, Which I think this sequence shows pretty clearly.

Yeah, after reading this sentence

showing what an umbrella does to the light and shadows at various power levels

I felt that it should be clarified. This is the beginners forum after all.

 

[TCampbell]

It's all about the "apparent" size of the light source.

I like to use an extreme example to make the point:

The Sun is roughly 1/2º from edge to edge (that's the diameter of the "disc" of the Sun. This seems rather small and a 1/2º wide light source casts well-defined shadows (just step outside in the middle of any sunny day) with hard-edges ... rapidly transitioning from light to shadow.

In reality, the Sun is 109 times wider than the Earth -- so it's a pretty big light source. But as it's also located about 93 million miles away... it seems fairly small.

Back to photography... when you use a light modifier such as a shoot-through umbrella or soft-box, etc. you are making the light originate from a nice broad light source rather than from a pin-point source and that softens the edges on the shadows... making soft gradual transitions from light to dark instead of a well-defined "hard" edge.

But it's not just about the true size of the light... it's also about how far away that light source is from your subject. As it's distance increases its "apparent" size becomes smaller and therefore the quality of shadow/light transitions will become harder.

The closer the light modifier is to your subject... it's apparent size becomes larger and it's shadows become software... but at the same time the light fall-off problem happens more quickly so the difference in brightness in your shadow vs. light areas will be more extreme. Add that together and if you need slower light fall-off AND nice soft light, then you need an extra jumbo size light modifier that can be placed at a greater distance from the subject and still have a large "apparent" size.

An interesting experiment in lighting would be to calculate the "angular width" (rather than "dimensional width") of the light modifier necessary to produce artistically soft shadows. You could then calculate the size the light source needs to be (the physical width) as a table for any given distance... where the light modifier size increases proportionately to the distance from subject.

I have not stumbled across such a table myself... but much of the "art" in lighting is really a matter of math & physics... so it's certainly possible to translate the artistic shadow quality you like into recommended angular dimensions.

 

[Trever1t]

The power level is irrelevant to the quality of light, what matters is the size of the light. I've seen tons of people get caught up in that; thinking that they can get softer light, or more rapid fall off, if they adjust the power of the light. Adjusting the power of the light changes the exposure value, but not the light quality.

Not alone yes, but if you lower the power and place the light source closer you effectively have increased the apparent light source AND softened the light WITH more rapid falloff!

 

[Derrel]

Big D,I remember the first time you posted this comparison: you got royally flamed by one of our resident flash gurus!!!! Interesting to see the responses this time around.

 

[Didereaux]

Big D,I remember the first time you posted this comparison: you got royally flamed by one of our resident flash gurus!!!! Interesting to see the responses this time around.

oh cripes, Oldtimerz strikes again. I had forgot that. Saw this in my misc folder and thought I had forgot it. arrrfh.

 

[Designer]

That's something I would do.