Diffusion Choices

[Eric Coughlin]

I'm looking for options to shoot some Area 48 LEDs through diffusion for a small studio setup to soften and broaden their output. I'm looking at the Matthews site here (http://www.msegrip.com/blog-content/?p=389) where it specifies the different types of diffusion. I'd prefer not to loose more than a stop of light (unless I need to), and less than a stop probably wouldn't diffuse it much.

In terms of silks listed there, there is "China Silk - White" which is specified as, "Softens light wihtout a great reduction of intensity. Indroduces a siginificant amount of ambient bounce." Then there is also "China Silk - Black" which is specified as, "Softens light without a great reduction of intensity."

Since I don't want light bouncing back and all over the studio and am planning to use it only to shoot through, and from the description it makes it sound like the black silks don't have ambient bounce, is a black China silk what I want?

I always thought black silks were used more to cut down light (like a scrim) and not to diffuse it. Will the black China silk diffuse as well as the white China silk?

I called Matthews and asked them but the guy on the phone didn't seem too sure of an answer (he did say the black silks aren't used or sold much), and I can't seem to find much info on using black China silks online.

 

[Grug]

For a simple, lightweight diffusion I'd look into 250 or 251, or better yet, Rosco Half Soft Frost (which has a really lovely shadow quality). Put your Area48 through a 4x4 frame of one of those and you can get a really nice soft key.

 

[Eric Coughlin]

From the Lee site here I see that the 250 is 3/4 stop loss, the 251 is 1/3 stop loss, and the Half Soft Frost is 1 1/2 stop loss. Lee also lists the color temperature of those diffusions as being 6774K; what does that mean and how does that relate to using a 5600K light source? Will the diffusers change the color temperature from 5600K?

Where can I buy the flags? All I could find was this information page from Rosco. Can I order them from B&H or do I need to call Rosco to order them?

What I'm looking to do is to put two Area 48 LEDs through a 4 x 4 diffusion with something like a Cardellini as you mentioned in the other topic (I'm thinking an Impact Grip Head with Fixed Super Clamp with an Impact - 40" Extension Grip Arm). Then have an identical second set of two Area 48's for fill light as in a studio setting I'd generally want even lighting. According to lux figures listed here, with two Area 48's with DP Choice Soft Boxes attached I'd be getting 3960 lux (1980 x 2) at six feet. Put a Half Soft Frost on it (36.2% transmission), and it becomes 1434 lux. According to this, that would give me about f/4 at ISO 200 (on a GH4 with a Speedbooster).

Of course those numbers are not including the second set for fill, so I'm not sure how much the second set from the other side would add to the lux values and exposure (would I gain around a stop?). I'd like to be shooting around f/4 to f/5.6, generally. The diffusion source would be perhaps 4-5 feet from the talent, and the light itself 6-7 feet. If the light is at say 7-8 feet from the talent, with 36.2% transmission, with just the key figuring in, it'd put me around f/3.3 at ISO 200 which is a bit more open then I'd like, hence why I'd lean more toward a one stop diffusion which would put me back at around f/4. But perhaps if the fill light actually adds in an extra stop the f/3.3 would be up from f/3.3 to f/4.8, in which case I'd still have enough light with the 1 1/2 stop diffusion. Of course it's easier to dim the light when desired than it is to make it brighter when already at 100%.

Any thoughts on using a black China silk to avoid the ambient bounce?

 

[Moseph]

I think you're waaaay over thinking the numbers here. Diffusion is a funny thing when it comes to light transmission, I'm not sure I'm buying those stop levels that LEE is stating. Just with a single type of diffusion, you can drastically change how soft your light is by walking the frame closer to your subject, walking the light away from the diffusion, walking both the light and diffusion in or out, etc. Your best bet is probably to go to a local rental house and ask to buy a few cuts off some rolls. 216, 250, opal, and 251 are the most common non-textile types of diff, it usually goes for $6 per foot. If they have some used partial rolls that got returned from a job you might get lucky and get them for free. Skin a couple frames with them and experiment, this will give you a real idea of what will work.

I've never seen or used black china silk but I can't imagine it would be a solution to spill. Seems to me like a material that would just cut light similar to bobinette. Just about all diffusion is white or translucent (it has to be in order to become a new, broader source when you point a light through it), so some light will inevitabely bounce back. When this becomes a problem, you'll have to flag it off or use chimeras.