Cinematography Basics: Lens Filters and How to Use Them
As you get to grips with the basics of camera and lighting, you’ll soon grow used to some of the various manipulations of image available in-camera and through the careful placement of lighting. But when looking for an image that’s more precise, more creative or just more wacky, it’s worth getting to know the types of lens filters available to you as a filmmaker. To understand filters is a rewarding effort, and one that will provide you with a whole new level of control over your image.
Here’s a breakdown of the basic types of lens filters:
Exposure (Neutral Density)
The purpose of all of the various types of diffusion filters is to soften the image and reduce its contrast. Like using soft light, these filters aim to lend a more ‘gentle’ and aesthetically appealing beauty-type look. Such an effect was popular back in the early twenties as a way of adding a stylised and glamorous look to the female star of a Hollywood movie.
As well as the classic glass filters that usually fit either onto the lens or in front/behind it, many cinematographers (such as Shane Hurlbut) utilise other methods, such as a silk stocking. By placing a stocking between the lens and the camera, a very subtle and impressive effect is produced.
In a pinch, various other methods of diffusion can be applied, such as putting Vaseline on the front of the lens (recommended only if prepared for some hardcore cleaning!) or simply grabbing hold of some cling film/plastic wrap and shooting through that.
Filters dealing with effects are diverse in their purpose, ranging from stylised Star Filters which spread out light in star shapes around its source, to Sunset Filters providing a heavy orange glow to your shot. Filters in all kinds of colours and creating all kinds of distortions can be found, although their extreme influence on the image often make the more popular in style-oriented productions such as music videos, rather than continuity-driven narrative film.
Colour Balance Filters
In order to achieve proper white balance when using film stock, the traditional method was to utilise warming and cooling filters in front of the lens. A simple example is the orange 85 Filter found in Super 8mm cine cameras; when film stock is used that is designed for indoor use under warm lighting, this filter allows for shooting in daylight (which is much cooler and bluer) without casting a strong blue tone over the image. Though less common, blue filters also exist with the intention of shooting indoors with daylight-balanced film stock. Today, in the digital age, most cameras have an in-built digital white balance setting, and so the use of these filters is far less common.
When reducing exposure, your first port of call will usually be to adjust the aperture of the lens using f-stops. However, when changing the f-stop setting, you also change the depth of field of a shot. This may be fine if you’re starting out and practicing with exposure adjustments, but once you start to consider the creative impact of choosing an appropriate depth of field, there’s just no reason to compromise it with other solutions available. Enter Neutral Density Filters, or ND for short.
These nifty little things change nothing of the colour or contrast of a shot; the only element they effect is the exposure. When a shallow depth of field is desirable but it’s just too bright for the highlights to avoid being blown out, an ND Filter solves the problem by cutting down the amount of light entering the lens, without changing the depth of field. ND Filters are available in a range of intensities, but I would highly recommend investing in a Variable ND Filter. They’re not too expensive when buying a cheaper version (£30/$50), although filters of the highest quality by a company such as Tiffen are more like £250/$300. Variable ND Filters allow you to change their intensity with a simple turn of the filter, a feature which is invaluable in saving time on-set. Invest in one of these and you’ll vastly expand your flexibility and precision in setting up shots just as you want them to be.
Lastly, a quick note about Circular Polarizing Filters, or CPLs. These filters are handy in a tight spot, when reflections are causing you problems, and also serve to improve the appearance of a washed-out, drab sky. By blocking out light in a particular direction (depending on which way you turn it) a Polarizing Filter is able to prevent light reflected at a specific angle from entering the lens. When shooting with a reflective backdrop such as a window, this is a great way to avoid the crew being seen reflected back at the viewer! Likewise, the details of clouds (due to their reflectiveness) can often be lost to the camera, particularly on a miserable, overcast day. Using a Pola Filter, again using the same principle, will allow more of the intricacies of individual clouds to be seen, providing a more textured and deep aesthetic to your outdoors shots. Polarizing Filters can be found easily at most photographic shops, due to their popularity for stills photography. A cheap brand will do a fine job for around the £5/$10 mark.
So there you have it. Though not an exhaustive list of all the possible types of filtration, the above should give you an overview of the options available for that extra level of adjustment you may have been missing from those all-important shots. When in doubt, filter it out!
This post, as all others, has benefited from a number of key sources. This includes not only my film school education and on-set experience, but also a variety of books and online materials. In all cases, I have reworked, combined and elaborated upon found and learnt information to provide a helpful and accessible post. For further reading on the above, please see Cinematography: Theory and Practice by Blain Brown. You can find my review of this brilliant textbook here.