Percy Thrillinghurst of Bath, England asks:
What can you tell me about diffusion filters?
As with so many aspects of cinematography, once you have an understanding of what diffusion filters do and how to apply them – which is easily found on the web – the rest becomes a matter of taste and experience.
Some cinematographers are dogmatic about whether or not they use them. As anyone familiar with this blog will know, I always let the story dictate my creative choices. During the film years, I went through a period in which I became fond of Tiffen Black ProMists, in grades from 1\4 to 1, and Mitchell Glass Diffusions, in grades A and B. I also sometimes placed nets in front of or behind the lens. No hard rule governed any of this; I simply liked what they did to the ever-sharpening Kodak emulsion. Similarly, to soften the inherent hardness of the digital image and make it look more filmic, I have sometimes resorted to such elements as Tiffen Glimmerglass and Schneider Hollywood Black Magic filters, both in grades 1 to 2. But the latest generation of electronic cameras have pretty much solved that problem, so I now lean toward shooting everything clean.
There is also a more compelling reason to not use diffusion at the lens. Virtually any filter effect can be matched in the DI suite in a non-destructive way. By not baking-in the look at the moment of exposure, you’ll retain the freedom to make finer, more appropriate decisions at a later date. It also ensures absolute consistency and also saves time and money on set, especially when working with multiple cameras.
Of course, certain non-diffusing filters still have their place in the kit. Straight ND’s (.3 to 2.1), 6×6 grads (hard and soft ND and colored), one and two-stop polarizers and attenuators are essentials. A large collection of them accompanies me on every job.
My best advice to anyone considering the use of diffusion over their lens would be to conduct extensive tests before committing them to the job. Shoot a variety of representative images, both with and without the glass or net. In post, a split screen is simple to execute and allows you to compare a clean image to a filtered one. Then, have the colorist create a matching effect. If you want to read up, there’s plenty of literature to draw on. The 11th Edition of the American Cinematographer Manual alone offers thirty-seven pages of detailed filter information.
And just when you might think everything has been said about the issue, I refer you to the new IOP series of lenses recently released by Angenieux. They feature an exciting new twist – internal filtration that can be easily changed out for a different look or application. The effect promises to be unlike anything we’ve seen to date. I’ll be shooting a series of tests with them in a few weeks and will report my results in this space.
Given the modern sensors, I usually just carry 3 filters: ND .3, Clear and a RotaPola.
ND Grads are great, but most of the other effects can be achieved in post.
Clear filters are needed any time you are not in a dry environment without wind.
Most of the digital cameras have internal NDs .6, 1.2 and 2.1; with an ND .3 you complete pretty much the full scale, missing only the ND 1.8.
I prefer to shoot sharp and soften up later, than shoot soft and been unable to sharpen the image. Different if I’d like to use smoke machines to make the environment hazy.
Luigi – ND grads are a must for taking down such things as overly hot skies or pavement. If you don’t do that at the lens, you won’t be able to recover the details in post. And often the cameras I use don’t have internal ND capability – PV DXL2, for example.
In the 11th Edition of the ASC Manual, I had Ira Tiffen enumerate the pros and cons for doing diffusion in camera or in post. There’s no right or wrong answer. You can also take what I call a 50/50 approach, use some lighter filter and then have the option of increasing the effect in post.
I find that if the goal of the diffusion filter is halation more than softening, then optical filtration tends to work better, you can get lights to flare with minimal loss of textural detail, whereas digital diffusion often blurs texture and when you dial it back, you get less halation. Unless you want to spend the time picking areas of the frame to diffuse and leave clean for more texture in the coloring suite.
That ultimately is the main reason to use filters, the time factor in post. If you are only softening a handful of close-ups, then doing it in post might make more sense plus you have so much more control, but if the overall project is meant to look diffuse and you have a thousand shots to add digital diffusion, it will eat into the time budgeted for color-correction.
Another factor to consider is political — if you are digitally filtering to make your leading actor look more glamorous but have a clean, sharp image on the set monitors and in dailies through editing, leaving the softening effect for the final color-correction may cause some issues. First, you don’t want to have to constantly promise to the actor (and their make-up team) that things will look better later in post, and you don’t want to run the risk that after spending weeks editing clean material, the director and producer might decide they want to leave it clean.
But ultimately the main reason I like using filters on camera is that it is fun, I see the effect while I’m shooting, I can play around with it on the set, etc.