Diffusion Question

JZASMM · Jan 25, 2009

Mr Mullen,

I was wondering how you would achieve the lighting effects in these images...

I am assuming that a soft filter is being used here, but how do you light it to get those effects? Is there a certain way that will get the best results, or would you just light the shot normally? Thanks.

Jacob

David Mullen ASC · Jan 25, 2009

Most of "Minority Report" was shot with a black net diffusion (basically a fine ultra-sheer black pantyhose stretched either over the back of a lens or on a filter frame in front of the lens). Kaminski has also used other filters like Classic Softs and ProMists on other Spielberg films.

Diffusion filters cause bright areas to "halate" (glow) so if you want to enhance the effect, you need some hot spots and bright kicks off of surfaces.

Black Net:

Classic Soft:

JZASMM · Jan 25, 2009

What kind of asa would you have to be shooting to get the hot spots on things that aren't going to be really that hot, like the blacktop in the first classic soft image you have there?

David Mullen ASC · Jan 26, 2009

It's not a question of ASA, it's a matter of exposure.

But the truth is, you rarely take a spot meter and read a bright kick off of a car or a wet street (especially if it is a momentary glare), you meter the subject and judge the hot spots around the subject by eye. You may adjust the composition so that important parts of the frame are not being obscured by lens flare and halation.

If you want that halation, you have to arrange to have hot spots in the frame, like shooting in backlight outdoors, getting the sun to glint off of water or cars, etc. Or shooting inside and having very strong spotlights on areas, bright lamps in the frame, etc.

You can usually see the interaction with the filter when you look through the viewfinder. Of course, if you are shooting video, you can see the effect right there on the monitor.

I've found over the years that you just have to be bold and put those intense spots in the frame and not worrying so much about metering them. As soon as you meter the hottest spots, you start worrying that they are too bright and you start knocking them down.

JZASMM · Jan 27, 2009

Okay, that makes sense. I was just wondering about the ASA, because I shot 250 with a ProMist 1 a few weeks ago outdoors, with the subject in shadow and everything else in the light. I didn't get much halation at all on anything, so that's why I asked. If I were to spot meter, what kind of ratio would I be looking to get between the hotspots and the subject?

David Mullen ASC · Jan 27, 2009

You want some hot spots to be as hot as possible, i.e. off the scale.

To see halation well, it's best to frame something dark behind the area that is glowing.

You can get a little outdoors, but generally the sun is only four-stops different from the shade out in the open, not a huge difference -- it helps to shoot somewhere more shaded but with hot sun striking into the area (like in the woods or between buildings) or late or early in the day on a really clear day, or shoot into backlight with shiny or wet objects that will cause the sun to kick off of them, etc.

Look at these shots from "JFK" -- the ProMist was probably a #1/2 in this case, maybe only a #1/4, but the overexposed areas are probably around five-stops over or more:

JZASMM · Jan 29, 2009

Okay, I get it now. I do have one more question though. In the final War of the Worlds picture you have there, of the ferry, there seem to be perfect... orbs I guess... around all the lights. They are here on the lamp too...

Why and when do those show up, because most other lights that are photographed with the soft filter just tend to diffuse the light, not make that neat, very sharp halo kind of thing. How do you get that?

David Mullen ASC · Jan 29, 2009

There are two common types of diffusion -- one involves suspended "mist" particles that cause bright areas to fog, like Fog, Low-Con, ProMist, GlimmerGlass, etc. do.

But real diffusion involves throwing an out-of-focus image over a sharp image. To do this, you need a pattern in the filter that throws areas out-of-focus but has clear areas that let a sharp image come through. In a black net, the lines of the net serve to diffract and soften details while the gaps in the net allow the sharp image to come through.

But with most glass diffusion filters, there is some sort of bubble or dent or other dimple in the glass that blurs the image at that point, surrounded by clear areas that don't soften the image. In the case of Classic Softs, there is a fairly obvious and regular grid pattern of round or circular depressions, a "lenslet". The size of that round dent affects how heavy the effect is. And what focal length lens you use will affect how large that circular concave bump is relative to the image size. So at certain focal lengths with certain degrees of Classic Soft, you end up with a small ring effect around the light (usually longer lenses); other times, it's more of a round bubble effect (usually wider-angle lenses). For example, here you see more of a ring forming:

Other diffusion filters (like Soft-FX or Diffusion-FX) use smaller and more irregular patterns, making it harder to see this effect. Schneider, who makes the Classic Soft, has made a version with smaller lenslets for people shooting HD where too much depth of field can make the pattern too obvious. I think they are calling this new pattern "HD Classic Soft" and they have a version of that combined with a Black Frost filter called "Hollywood Black Magic".