(Excerpt taken from my film book, “Shooting Better Movies: The Student Filmmakers' Guide.” Available on Amazon. See end of post for link)
Some cinematographers like to use camera filters and some like to shoot clean, with nothing in front of the lens at all. it all depends on the look you're going for and you're own sensibilities. Filters can be a great tool to have on set to darken skies, diffuse the image, or remove reflections. Let's take a look...
Filters can come in two forms. One internally within the camera body or externally as a piece of glass that can be placed in front of the camera by sliding into the attached matte box.
NEUTRAL DENSITY FILTERS
Some cameras come fitted with a selection of built-in neutral density (ND) filters of varying strengths. Neutral-density filters reduce the intensity of the light, yielding no changes in color rendition. The director of photography can use them to reduce light in order to change aperture or shutter settings. ND filters are like a pair of sunglasses. When things become too bright outside, you put sunglasses on to see better and to not have to squint. They come in various strengths and different densities to help cut out the light entering the camera. Common strengths are 0.3 ND, the equivalent of 1 full stop down in aperture; 0.6 ND, 2 full stops; and 0.9, 3 full stops. ND filters are basically gray glass. When a filter is placed in front of the camera, the camera assistant will mark up the side of the matte box with tape or a sticker displaying what filter is being used. This let’s everyone in the camera department know what filters are in play without having to remove them each time to check.
ND filters enable you to have more control of the f-stop; use them to reduce your depth of field. Say you have some foreground action that isn’t as soft or out of focus as you would like, or the background is still quite visible. You have your image at a given exposure, say, f/8, which you would like to be at f/4. Using the camera’s ND filters or a glass version in the matte box at a strength of 0.6 darkens your image. Then, you can open the aperture to F4 (2 full stops wider than F8, equivalent to 0.6) to achieve the same image brightness you had before applying the ND filters. Now your aperture is wider and your depth of field therefore smaller. So you are using the ND filters to give you that shallow depth of field look and move away from the TV news feel of deep focus.
Full ND filters are gray all over the glass from top to bottom. There are also filters which are graduated; they are gray at the top and gradually fade to clear at the bottom. These filters are great for filming skies where the foreground image of the subject is well exposed, but the sky is blowing out or overexposed and reading as white. Let’s say the foreground action is exposing nicely for f/5.6, and the sky is three stops over and needs to be exposed at f/16 to see the detail and clouds properly. If you stop down your aperture to f/16 for the sky, your foreground will be too dark. So what could possibly be the solution? Graduated ND filters! Find a filter with a strength of 0.9, place it in front of the camera, and then the sky and the foreground will be properly exposed. Graduated filters come in two forms with differing graduation. One is soft edge (S/E), with a smooth, soft fading out of the ND or filter color; the other is hard edge (H/E), which is a more straight, hard line between the filter and the clear side.
Another good use of ND filters is for dramatic effect. Maybe your sky and foreground are correctly exposed already, but you choose to put a 0.9 ND grad filter in front of the camera. Now, if you’re filming on an overcast day with white clouds, putting on a 0.9 ND graduated filter will send your white clouds to gray, or gray clouds to very dark gray, giving the impression of an approaching storm. I’ve even used them heavily on a nice, clear, blue sky. Adding graduated ND filters to the camera made the sky a darker blue at the top of frame, slowly fading to a lighter blue at the bottom. They have many uses to the DP, and it is about just being creative with the tools available.
When light is reflected it bounces around or vibrates everywhere. A polarizer filter passes only the light coming in from one direction. This is very useful when you are filming glass or anything with a reflection. A polarizer can be rotated in the matte box in various degrees to help reduce reflections on glass or reflected objects. It also helps darken the image by about 1½ to 2 stops and boost colors when filming skies and water. It does this by filtering out the polarized component of the light and increasing the contrast in the image.
Black Pro-Mists are a favorite of mine and are an example of a diffusion filter. They come in various strengths and types, including 1/8, 1/4, 1/2, and full. They are a soft-focus filter, reducing the value in the highlights and lowering the contrast. It does mean a little loss in detail, but some camera operators constantly use a 1/8 strength filter in front of the camera just to take that edge off the super sharp and clear high-resolution images. Diffusion filters also help reduce wrinkles and blemishes in the face of your talent.
They also give a soft, tiny halo effect to highlights, which can add a magical or enlightened look to the shot. Take a look at these shots of a candle to see the effect it is having.
So there you have a few examples of what can be achieved by using camera filters. There are many more to chose from that I haven't discussed here, so I encourage you to go and research all the different types you can and see what effects they bring.
"Shooting Better Movies: The Student Filmmakers' Guide" is published by Michael Wiese Productions and is available to buy from Amazon here:
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