How to expose

Steve Fairclough explains some of the key exposure factors you need to consider when shooting videos

Some of the key factors you need to consider when shooting video

If you’re new to shooting video, don’t worry – the basics concerning apertures, shutter speeds and ISO values remain almost the same as shooting stills. Depending on the camera you’re using, you may have the option to shoot with very low compression or even raw video. This will give you much more flexibility when it comes to editing your video and will also allow you to recover some shadow and maybe some highlight details. That said, our advice is to try to get the best possible footage straight out of the camera, so here are a few good exposure pointers to help you achieve that.

Stick to a low ISO

As with stills, the higher the sensitivity the less light is required to expose the frame. However, due to the shutter speeds that are used for video, the sensitivity will generally be at the lowest possible settings – ideally ISO 100, but ISO 200 or 400 will also suffice.

Using a higher sensitivity can introduce noise. This may be acceptable for some still images, but for video noise is more random and shadow areas can be prone to looking fuzzy. They may change at a rate of, say, 24 times per second (if you’re shooting at 24fps), which can be highly distracting. So, it’s best to stick to as low an ISO value as you can.

Shutter speed limitations

For shooting digital video, the shutter works a little differently than for capturing stills. With stills photography you’ll be relying on a mechanical shutter but when recording video, the noise of the shutter would be picked up. So, instead, the shutter opens at the start and then an electronic shutter simulates the function of the mechanical shutter as you film.

When shooting stills, you can choose almost any shutter speed (up to 1/8000sec or even long exposures of several seconds) depending on what effect you want to achieve in the final image. The critical difference between the two disciplines lies in the fact that for video you’re limited to a single shutter speed while filming, a speed that will depend on the frame rate you are shooting at.

Aperture values

As with stills photography, the aperture setting controls the depth of field, as well as the amount of light coming into the camera through the lens. The restrictions on what shutter speed can be used for video have a big impact on the aperture settings you can use.

In TV and films, a shallow

depth of field is often used creatively to isolate the subject. One of the advantages of shooting with a DSLR that has a large sensor is that you can reproduce this look and hence give your videos a ‘filmic look’. In the past, video cameras with smaller sensors couldn’t replicate this shallow depth of field, which is why most amateur videos have front-to-back focus.

Try using careful focusing and a shallow depth of field to give your videos a cinematic effect but don’t go overboard on using this style since overuse may look like you can’t film in different styles. Use a wide aperture from about f/2 to f/5.6, depending on the lens and how much of the scene you want to appear in acceptable focus.

The role of ND filters

In certain scenarios, to prevent overexposure, stills photographers will often adjust their shutter speed. However, because you can’t do this with video you have to use ND filters to reduce the amount of light entering the lens. For shooting video, ND filters work in the same way as they do for stills photography and, depending on their strength, can cut out the number of stops of light from 1 stop right up to 10 stops (or be combined to do so). In fact, some cameras, such as Canon’s Cinema EOS models, have built-in ND filters that you can adjust in-camera.

A popular filter for filming is a variable ND filter – a single circular filter that can be adjusted between 2 and 10 stops. The advantages here are the wide range of stops available and the fact that you can subtly adjust the exposure while filming. It is worth investing in a good ND filter as some of the more budget versions can cause colour casts or strange light patterns.

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