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diffusion breakdown


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#1 allnetfilms

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Posted 14 May 2005 - 02:25 PM

Please help. I am trying to guide my steps in buying diffusion and gels.

Trying to understand the what families of diffusion are supposed to do and in what circumstances I might want to reach for a certain type. For example 216,250, 251(i understand these are different strenghts) vs the frost family vs grid cloth family, etc. Is muslyn(sp) considered diffusion?

Anyway, I just need general guidelines about what they are going to do to the light passing through it and under what circumstances seasoned DPs reach for certain diffusion. Besides the obvious which is to soften the light source.

Also does anyone know of an inexpensive way to house and keep the gels/diffusion organized. I've seen milk crates with labels is that the best way.

Thanks!

-D

Edited by allnetfilms, 14 May 2005 - 02:28 PM.

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#2 Kevin Zanit

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Posted 14 May 2005 - 08:09 PM

Well first let me say this:

I honestly break diffusion down this way:
Heavy
Medium
Light

In the Heavy category would be 216, Full grid, 100H, and silk
The Medium would be 250, Light grid, etc.
The Light would be Opal and Hampshire frost

The above are just a few, I am sure there are many more that go into the various categories, I just haven't memorized them all.

The differences between the ones in the different categories are relatively minor, especially in the heavy category.

Now in a large frame (like 12x12) I find Full grid is a lot different than silk, in that it diffuses it more with less light loss, but honestly most of the differences are minor.

Some may totally disagree with me, and are extremely specific about what diffusion they use, I just know what quality I want, and match that to a specific grade (light, medium, or heavy).


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#3 Kevin Zanit

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Posted 14 May 2005 - 08:16 PM

And for the storage issue:

It depends what size piece of gel you are talking about. In bigger shows you use a gel cart to hold various rolls of gel. It is just a rolling cart with tubes to hold the rolls.

You generally put cut pieces of gel in a "gel crate" which is just a milk crate. Some just roll the piece up, and dump it in. Others (like my gaffer) have a fairly well organized one with show card inserts to separate the different types. His is organized like this:
CTO (he puts all grades of CTO in this area)
CTB (he puts all grades of CTB in this area)
Diffusion (he puts all grades of diffusion in this area)
and Party colors (he puts all types of miscellaneous gels in here from strong reds and amber, to plus and minus greens, etc, etc)

The point of this is to just have commonly used gels near the set. If we don't have a gel cart we just keep the rolls of gel on the truck.

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#4 David Mullen ASC

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Posted 14 May 2005 - 08:40 PM

There is too much artsy mumbo-jumbo surrounding different diffusions. The individual types of material (cloth versus plastic versus paper) used have some small affect on the "texture" texture of the soft light (how much specular light mixes into the soft light) and even may affect the color slightly, but the main difference is in how dense the material is and how efficiently it spreads light (which is why I don't use silk much, because it doesn't spread the light very well, creating a star-shaped hot spot. However, it is one of the quietest of materials outdoors in a breeze, so it is still very useful.)

The softness of a light is dependent only on the SIZE of the source (in this case, the diffusion, not the light behind it) relative to the subject -- i.e. a big diffusion far away can be similar in softness to a small diffusion very close. From the subject's perspective, for example, you could place a 20'x20' diffusion frame at a distance and a 4'x4' frame up close just to one side, and to the subject, both frames may look the same size in their field of view, and thus they would be of the same softness. The difference though is in FALL-OFF; the farther, larger diffusion would fall-off in intensity more gradually. With a diffusion up close to a subject, simply leaning towards or away from the source may cause a visible change in brightness.

However, all of this assumes that the light is filling the diffusion completely evenly and from edge to edge. A thinner diffusion may produce more of a hot spot in the center of the diffusion, so the "size" of the source is not quite as large when it's not filling the frame, and thus the quality of the shadow produced will be a little sharper.

There are no hard or fast rules about this; you can make the light very soft or barely soft according to taste and need.

Besides wanting to keep the light a little less soft, another reason for the lighter diffusions may just be that there is too much exposure loss from the heavier ones.
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#5 Paul Bruening

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Posted 17 May 2005 - 10:27 PM

Hello,

Rosco describes the characteristics of thier diffusion materials. You'll have three primary concerns: 1. Does the material broaden the source? 2. Does it affect color? 3. How much does it reduce the source's foot candles. For example, silks are beloved by cinematographers. However, they don't tend to broaden the source as well as spun materials. Yet they also don't cut the footcandles as much as spuns. Often, bounced light can do all that you need diffusions to do and cost less. 1", one sided styro from construction supply houses or foam core from art supply stores can do wonders to broaden sources with light loss being predictable with distance and beam spread.

Hope that helps.
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#6 allnetfilms

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Posted 18 May 2005 - 10:07 AM

Thanks! That does help. :)
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