Paul C. Buff, Inc. Technical Forum

Sorry, no pix yet. Maybe sunday or monday.

Luan had told me that the omni with the triple sock would give you approximately the coverage of the 53" parabolic. I can tell you that this is way off the mark.

I shot a full length test shot of myself using the 53" para with sock, buff 36" octa and omni with the sock, all with the front of the "box" about 3' from the subject.

The amount of coverage was very good with the 53", ok with the 36" octa and bad with the omni. That's about what you'd expect but based on conversation in another thread I was expecting to be surprised by the omni.

In all 3 cases. the falloff was a bit more than I would want for a full length but the 36 fell off too quickly and the omni was the worst. I should have compared it to my kacey beauty dish. I'm hoping to use the omni outside but based on these tests I'm not sure I'm going to keep it.

I'll use it for some beauty lighting over the weekend and decide then...

The angle of coverage of the Omni is as wide as the diffused PLM™ or any soft box or wide angle reflector - 120°+. Correct measurement or definition of coverage angle mandates the surface is an arc, with the light source at the center point of the arc, hence the word "angle".

What you are seeing is the normal effect of inverse square law . . . the extremities of the subject are further from the light than the closest portion of the subject.

The falloff you are seeing is actually the desirable "quality of light" from a beauty dish style use of a modifier. Normal practice for beauty dish style lighting is to place the modifier within about twice its diameter of the subject in order to purposely accentuate the light intensity of the body parts nearest the light - normally the face and usually at a side angle such that one side of the face is brighter than the other side.

This creates "mood lighting", with strong gradients of light to dark across the model.

In order to evenly light a standing model from a distance of 3' away would require about a 60" soft box. Even then you would have a "light side" and a "dark side" unless you lit straight on and stood in front of the soft box, or used a second soft box on the other side of the subject to counter the falloff and shadowing.

A Kacey BD will act the same as the Omni™ with the placement you described.

Yes, i've used a beauty dish for years and am very familiar with its properties and I understand the inverse square law and light gradation. However, you told me in the other thread that the Omni with the sock had the same angle of coverage as the 53" plm at the same distance. That is just not true. And I didn't think it could be true given the size of the modifiers but thought I'd give it a try based on your recommendation. From what I can see, the omni has less coverage than the Kacey 22" beauty dish which is what I'd expect. Not necessarily what will work for me. But I'll be testing it tomorrow with a model for headshots so we'll see how it goes.

So given the physics of the light, it's behaving as I would expect. It was your previous explanation (you can go back and read the thread if you want) that caused me to think there was some kind of magic going on with the sock and the angle of the omni reflector

Can you post a link so I can see exactly what was said please?

I think we are discussing angle of coverage vs the surface area covered at a given distance. The surface area covered, when a modifier is used close to the subject in comparison to the modifier's size, will indeed vary with the modifier size.

For example, visualize a small bare-bulb and a 60" softbox, both placed 6" from the center of a standing model. The bare bulb with have a large falloff at the head and feet, even though it has a 360° angle of coverage. But a softbox, even with a 30° grid, will light pretty evenly from head to toe, due simply to it's size.

I hope my previous comments weren't misleading to the point of anyone interpreting them as saying one could place an Omni 3" from a wall and expect the wall to be illuminated evenly from floor to ceiling.

This would defy the laws of physics, particularly the inverse square law of light propagation . . . magic.

We don't do or claim magic.

Sorry if you felt mislead.