Comments on: How does a Shoot-Through Umbrella Work?

By: Terri Ann

Terri Ann — Tue, 29 Dec 2009 02:59:19 +0000

Thanks for the comment Christoffer – you are right, I based these diagrams around the concept behind the way a glass but I think it makes a good jump point towards understanding how the umbrella manipulates the light. The larger or smaller the umbrella the less of an angle the light will be spread, even with a shoot through umbrella. Though the point that the white cloth spreads each “ray” in multiple direct once it leaves the umbrella does help create the wrapping effect of the lights.

Though this diagram is invalidated, to a point, when you think about how the closer or further away a light source is from the umbrella; how differently the light spreads. This also has to do with the spread of the light source itself.

This diagram helps illustrate some of the concept of a shoot through umbrella and Christoffer I greatly appreciate your comment – feedback even when contradictory to what I have said (no matter who is more accurate) is always valued here!

By: Christoffer Wallstenius

Christoffer Wallstenius — Sat, 26 Dec 2009 23:10:55 +0000

I actually consider this description to be wrong and misleading. Although the optical principles described are correct for an transparent material such as glass, it’s not true for an opaque material such as white fabric used in shoot through umbrellas. Instead, every point on the surface of the umbrella turned away from the light source will radiate light in all possible directions (hence, as a hemisphere originating from that point).

What really causes the softening effect of the light and shadows is not that the umbrella is expanding the spread, but that the umbrella is expanding the size of the light source as seen from the object.

A naked flash head, as seen from the object, occupies a very small space in the field of view. Hence, “light rays” originating from the flash heads will come in a very narrow “cone”, creating crisp shadows. From the flash heads pow, the light rays spread out like a cone, but from the objects point of view, the cone of light seems very narrow, since only the rays that “hit” the object straight on is “seen”.

If we throw in a shoot through umbrella between the flash head and the object, what do we get? Well, the “cone of light” from the flash head hits the much larger opaque umbrella. I.e. it makes the back side of the umbrella radiate light in basicly the shape of a hemispere. But, from the objects point of view, the light rays are now originating from a much larger source. The rays are comming in from different angles, therefore creating softer shadows.

Best regards, Christoffer Wallstenius

By: Ken

Ken — Thu, 24 Dec 2009 18:09:50 +0000

Great diagrams Terri!! I really like the way you’ve broken down how the shoot through umbrella works. I’ve always known that is diffuses light but never understood how.