Lights: Focusable and Open-Face
All light sources, such as studio lights, have two separate distinctive qualities: focusable (with a control knob or mechanism) and open-face (without a control mechanism). Each produce different light beams and intensities: wider beams create floodlights; narrower beams create spotlights (more intense light). By considering the different results produced between these 2 different types of light sources, it will help determine which will work best with achieving the desired look you’re wanting.
The focusable light source has a control knob that enables the user to focus the light. By pushing the lamp light back (toward the inside of the light fixture, just in front of the spherical reflector) a directional beam of light, spotlight or hard light, will be produced. These focusable light sources are known as fresnels (pronounced fray-NELL) because they use the same lens technology as Fresnel lens which were developed for use in lighthouses.) Consequently, if the lamp is pushed forward, toward the lens of the light source, a floodlight or softer light, or larger beam of light, is produced. Having focusable light sources may come in handy since it is after all like having two types of light sources in one and this is convenient. However, lights with focusable knobs can become expensive, but may be well worth it. Arri is one well known company that produces high quality lampheads with fresnel lens.
The open-face light source has a fixed lamp and is only able to produce one type of beam, an opened flood of light. However, users are still able to manipulate the light source by using flags, barn doors, reflectors, etc. in order to create different types of lighting on their subject(s). Open-face is relatively a vague term since with this specific type of light source, the face is either just a lamp (without any glass, etc.) or a flat and solid piece of glass and/or with a wire mesh (not distinctive like the concentric patterns on the Fresnel lens). In addition, open-face lights are light in weight and affordable, but be prepared to purchase additional modifiers such as flags, scrims, screens, reflectors, etc.. Lowel produces great quality open-face lighting kits and even has some fresnels.