Color Filter

You need color filters when the light source and your camera setup don't match — or when you deliberately want to set a color cast. The classic scenario: daylight outside, but your HMIs are still running on 3200K tungsten. Instead of reconfiguring everything, you screw a CT Blue (Conversion Filter) in front of the lights and bring them down to 5600K. Conversely, you can warm up daylight with CT Orange (also called CTO) if you want to work with tungsten color temperature indoors. The filters are made of colored glass or heat-resistant plastic film — glass is of higher quality but also withstands heat better.

On set, you place filters either directly in front of the light source (light-side) or in front of the camera lens — you tend to do the latter with smaller cameras or when you want to subtly create a look. You often combine ND filters with color filters: a CTO-ND combination allows you to create warm light while keeping the aperture open. This is standard for outdoor shoots with video cameras, where you typically tend to overexpose.

Important: Color filters reduce light intensity — a strong CT Blue easily absorbs 1–2 stops. You have to calculate this beforehand, otherwise you'll suddenly need more power and the lighting setup will become more expensive. Quality filters from established manufacturers maintain color deviation linearly across the entire spectral range; cheap filters distort individual color channels and lead to color casts in post. While this can be corrected in editing, it's cleaner to get it right on set.

Professionals also use converted cameras — with built-in color filters in front of the sensor — for consistent log output over several days. This saves you calibration during white balance. And no: the camera's white balance doesn't replace physical filters. The sensor does the calculation but loses information; real filters work with real light.