Exposure refers to the amount of light being captured by the camera. One of the most basic photographic principles, exposure is directly connected to the brightness and darkness of the image.

• An image is said to represent normal exposure when it is similar to what the eye sees. Over exposure happens when too much light is reflected into the camera, rendering an image that is brighter than normal exposure. Under exposure is the opposite: not much light enters the camera, thus creating a dark image.

Creating ideal exposure is often a cumbersome task because some factors are controllable, while others are not. If we are shooting under daylight, obviously we cannot turn off or dim the sun; we must either adjust the camera settings to create the exposure desired or move to a different location. Another possibility is flagging sunlight. If we shoot in a studio, then we have absolute control over lights.

Perfect exposure is subjective because exposure is a creative act. Thus, its properness depends on what is intended by the filmmaker. Underexposure, for instance, is often purposefully used in horror movies to provoke suspense or fright. Subtle overexposure is often used during dream sequences or flashbacks.

Light Meters:
Controlling light is an essential skill for a cinematographer. During usage of film stock, light meters are the only possible way to measure the intensity of light. With that reference, cinematographer controls light and exposure. But today with Digital cinema cameras, usage of light meters has become a rare practice because the cameras offer ‘histogram’ to calculate exposure range.

Histogram:
A histogram is a bar graph that was originally created for statistical analysis. As digital photography was developed, designers incorporated histograms into cameras to provide a graphic representation of the digitally recorded image.

However many cinematographers feel that even today histogram function is not fully understood and the information they provide is often incorrectly used.


Digital camera creates a histogram that describes the tonal range of each scene captured. The camera's processor locates each picture element (pixel) on this horizontal scale according to its relative brightness from 0 (black) to 255 (white). Pixels of equal brightness are stacked vertically one upon another to create lines of varying heights. The result is a graph of very fine vertical lines that can appear as a smooth curve, a series of uneven lines, or a combination of both.

Histogram graph is studied by having in mind that extreme left side is for under exposure and extreme right side for over exposure. If the graphic lines touch extreme left then some parts of the image is under exposed or darker, the same opposite way if the graphic lines touch extreme right some parts of image is either over exposed or brighter area.

For proper exposure value is judged from the indication of the histogram lines is fairly centered within the histogram graph.

But also when we are exposing the image like ‘white egg on the white cup’ then histogram lines tend to move right side, then if a ‘black pen kept on a dark color table’ histogram lines will move towards left side, so it is not that the subject is over exposed or under exposed.

Many professionals argue that histogram cannot detail about lighting ratios, the best flash / ambient mix, or whether the subject is properly exposed. That is why using a light meter; along with camera's histogram is the best way to ensure optimal results that can be easily reproduced.

There are two types of light meters:

• Incident light meter (The meter that reads the light falling on the subject from all angles)
• Reflected spot meter (reads light reflected from the subject).

Most popular light meters are Sekonic L - 758 Cine, Studio deluxe L -398 A.

Sekonic L – 758 CINE
Sekonic L-758CINE offers the latest digital video camera features and settings, has the most extensive range of fps (frames-per-second), ISO, cine shutter speeds, and shutter angle settings. With this camera dynamic range can also be entered.

L -758 cine can be used to create a Latitude Display that mirrors the range of your system. This important guide will enable to know the readings fit within the latitude and outside the range.
L-758 offers both incident / spot readings and powered by CR123A Lithium Batteries.

Sekonic L - 398A:
Sekonic L-398 A is termed as manual light meter or analog. It uses an amorphous photocell that generates its own power; there is no need for a battery.

This classic light meter is a favourite among cinematographers for its accuracy, readings are calculated by setting ISO and measured light readings are indicated by the needles.

• Instant reading of full range of aperture / shutter combinations.
• Amorphous photo sensor eliminates need for batteries.
• Continuous reading plus needle lock for easy and accurate readings.
• Swivel Head to position incident dome and maintain full view of display. 
• Lumi disc for adjusting illumination contrast and measuring illumination intensity. 
• Lumi grid for measuring reflected light. 
• Supplied with Lumisphere, Lumidisc, Lumigrid, High-slide, case and neck cord.

During bright exteriors a high slide is used in this light meter to take light readings.

Sekonic Prodigi Color C-500:

Sekonic C-500 is very useful tool for today’s digital cinematographic applications. The PRODIGI COLOR C-500 is the first photographic color meter that measures and displays color temperature and compensation values for both Digital cameras and film. Working on location with today’s mix of tungsten, halide, vapour and fluorescent lights can be challenging. The C-500 gives the control to balance sources and accurately reproduce color tones from set to set.  In Digital Mode, the color temperature and compensation readings are based on human visual response. In Film mode, readings are based on the color characteristics of traditional photographic film.



Author:
CJ Rajkumar
Author/Cinematographer