Diffuser size vs distance - any formula available?

SkipD wrote in post #17924731
Light can be bent many ways. Light is definitely being bent by the various elements in your lenses. Light is bent when going through water at an angle. Light can be bent when going through pockets of air that are more moist than surrounding air.

That's not a bend. And it's muddying the point put. Light doesn't just randomly bend round objects. It doesn't happen no ifs or buts.

digital paradise wrote in post #17925010
That I'm OK with. Makes perfect sense for lenses because that is what they do. I just thought it won't bend around something a brick.

You were right first time.
Light doesn't just bend in that way.

To be perfectly correct though, the law would be that 'light travels in a straight line through a vacuum'. How close is the atmosphere to a vacuum for that rule? Generally very close, so light travels at the speed of light and we teach the inverse square law as close enough to the truth.

So the light making a shadow never bends round a solid object, what actually happens is that we're not dealing with a point light source, and we're not in lab conditions, so the shadow breaks down because of light pollution from other directions.

Hope that's clearer.

What PhilV says. Do a test with and without a grid on the same modifier.

I at one time spent a lot of money on all the gismos out there trying to find the perfect on flash diffuser. After taking a few lighting courses and hanging around here realized it was pretty simple and just basic physics.

so take that last light source and add a grid, much more contrast because the light is collimated.
https://en.wikipedia.o​rg/wiki/Collimated_lig​ht

windpig wrote in post #17925370
so take that last light source and add a grid, much more contrast because the light is collimated.
https://en.wikipedia.o​rg/wiki/Collimated_lig​ht

Thanks. That is interesting.

windpig wrote in post #17925370
so take that last light source and add a grid, much more contrast because the light is collimated.
https://en.wikipedia.o​rg/wiki/Collimated_lig​ht

So, correct me if I'm wrong, but a grid would therefore concentrate the light but also make it harder.

And lets throw CUfocus grid on the mix

http://www.lighttools.​com …ced-secondary-nearfar.htm

Take a look
The gridded light doesn't get the cross-contaminating light from other parts of the diffuser, but still has the same shadow transition.
The cross-contaminating on the ungridded acts as fill.
Top is shot with grid

windpig wrote in post #17925481
Take a look
The gridded light doesn't get the cross-contaminating light from other parts of the diffuser, but still has the same shadow transition.
The cross-contaminating on the ungridded acts as fill.

could you label each photo, so we know with certainty which is which?

Top image in each post is the gridded modifier (36" octa 36" from mankin)
Lower is ungridded (same modifier, same distance, same angle)
There may be a small amount of bounce off a white wall camera left. The modifier is feathered slightly camera left of the subjects right shoulder (camera left shoulder).

Basically you are re-directing night, not bending it. Like playing pool with light.

windpig wrote in post #17925481
Take a look
The gridded light doesn't get the cross-contaminating light from other parts of the diffuser, but still has the same shadow transition.
The cross-contaminating on the ungridded acts as fill.
Top is shot with grid

Hosted photo: posted by windpig in
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forum: Flash and Studio Lighting

Hosted photo: posted by windpig in
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forum: Flash and Studio Lighting

Fantastic illustration - thanks so much for doing this so we don't have to!

my pleasure. I'm glad it may be of help to you.