Digital Video - November 2008 - (Page 42)

DV 101 BY JAY HOLBEN MEASURING UP DON’T FOOL YOURSELF — LIGHT METERS REMAIN ESSENTIAL TOOLS IN THE DIGITAL AGE. I n the days of old, back when motion pictures were solely recorded on a thing called film, the cinematographer was known as a kind of fortune-teller/magician who could magically read the light in the air and know exactly how the image would end up on the screen. Instead of a magic wand, or a crystal ball, the cinematographer’s best friend in this sorcery was their light meter. With the advent of video cameras and, later, digital video cameras, this magical ability to predict the photochemical future went by the wayside as — when technology caught up — one could actually see the final image on a monitor in real time. For digital shooters, this practically rendered the light meter obsolete as it was tossed aside in favor of “lighting from the monitor.” This has led to a generation of camera people who believe that you never need a light meter, and worse, have no idea how to use one when they discover that they do need it! First off, to understand a light meter, you need to have a fundamental understanding of the concepts of exposure in general. (For a refresher, see my DV101 Blog entries at DV.com from January 22 and 25 of this year.) A light meter acts on the fundamental principle of “proper” exposure, which — as the meter knows it — is middle gray, also known as 18% reflectance or Zone V. This middle gray is the “sweet spot” for all photographic mediums and is (more or less) the point at which light is recorded exactly as it is to the eye. The light meter assumes that everything you are photographing is an 18% gray surface and will tell you at which aperture you need to expose your subject to render it medium gray. That may seem odd, but it actually works quite well, as I’ll explain in a moment. The light meter can’t just magically tell you what to do — it needs some information: your shutter angle and frame rate (which, when combined, become your shutter speed) and your camera’s sensitivity (ISO, ASA, EI). The meter then utilizes a photosensitive cell to measure the intensity (brightness) of the light and calculates that against the given information to report a given aperture at which to “properly” expose the scene. From there, it is the cinematographer’s creative input that determines how that information will be used. There are two main types of light meters: incident and reflected. An incident light meter measures the amount of light falling onto it. The meter becomes a substitute for the subject being photographed and can measure the light directly from the source. These are the meters with a white disc or white ball on them, which is often called a “ping-pong,” as it looks like half a ping-ping ball. The ball is intended to represent the curvature of the human face. The simplest method of using an incident meter is to place the meter at the subject’s position (i.e., where your talent’s face will be) and to point the ball at the camera lens. All of the various light sources that will be hitdv november 2008 My trusty Sekonic, complete with “ping-pong.” ting your talent’s face will hit the ball and the photocell inside the meter will average out that light to give you “proper” exposure. An alternative method preferred by most cinematographers is to point the meter directly at each light source and measure each independently and then decide how to expose the scene. When taking a measurement, the meter assumes that the object you are photographing is a perfect 18% gray surface. In reality, you’ll very rarely be photographing a perfect 18% gray surface, but the beauty of an incident meter is that it will give you the proper exposure for nearly any item you are photographing. To explain, let’s assume that you are, indeed, photographing an 18% gray wall. You have 550 footcandles of light falling on the wall, which reflects back only 18% of that light, or 100 footlamberts (footcandles is the measurement of incident light falling on a subject, footlamberts is the measurement of reflected (visible) light bouncing off an object). The meter reads the light falling onto the wall and tells you at a 100 ISO at 1⁄48 shutter speed you need to expose the wall at a 2.8 to render it medium gray. If you shoot that wall now at a www.dv.com 42 http://www.DV.com http://www.dv.com

Table of Contents Feed for the Digital Edition of Digital Video - November 2008

Digital Video - November 2008 Contents AG-HMC150 Camcorder I-Cuff Eyepiece Protector Instant Expert Avid Media Composer 3.0 DT-B9L 1DU Monitor Flolight LCD500 Dark Red Close-Up: Chop Shop Socky Prime Mover Tools & Technology: DV Expo Toolkit Click to Play DV101 Production Diary

Digital Video - November 2008

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