F-stop is a Cinematography term in filmmaking. In virtual production, the nuances of this term take on special meaning. Here, we break down the definition to give you a starting point.
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F-stop, also known as the "focal ratio," is a term used to describe the mathematical measurement of the aperture of a lens. It determines how much light it lets in and affects both exposure and depth of field. A T-stop is an actual measurement of the light transmitted through the lens, which can be slightly different than the f-stop due to glass quality variations.
The 'f' stands for focal length divided by diameter, indicating the size of the opening inside a lens. As such, when selecting lenses for virtual production, it’s important to consider f-stops – not just its focal lengths. The lower your f-stop number, the larger the hole that allows more light into the lens; conversely, the higher your f-stop number, the smaller the hole that limits light entering the lens.
For virtual production, experts recommend using lenses with f-stops between 2. and 4. for ideal results. Although cameras vary widely when it comes to their ability to capture images with perfect f-stops, some top contenders include Arri Alexa Mini LF, Canon C500. Mark II, Sony FX6, Panasonic S1H, and RED Gemini 5K. When shooting scenes with these cameras, one should pay attention to f-stop to ensure they are getting the desired amount of brightness in the scene.
Different f-stops have tremendous potential to change the mood or look of a scene. For example, if you're trying to create a dreamy look for a romantic moment, then opt for wider apertures (i.e. lower f-stop numbers). On the other hand, if you want to increase sharpness and keep more elements in focus, try narrowing down your aperture (i.e. increasing your f-stop numbers). No matter what type of scene you’re shooting, understanding how f-stops work and choosing the right ones will help you get the most out of your virtual production projects.