essential skills: photographic lighting
Latitude Latitude is a measure of the ability or inability to record detail in subjects with extreme contrast and variation from correct exposure. It is an accepted rule that most modern film emulsions and digital image sensors have an approximate five to seven stops latitude, although this is sure to increase as manufacturers develop new technology. This means that if you underexposed an 18% gray card by three stops it would appear black on the image. If you overexposed it by three stops it would appear white. The human eye has almost limitless latitude because of its ability to compensate for changes in contrast and light levels. Film and image sensors are incapable of doing this due to their limited latitude. Color transparency and most image sensors capturing in JPEG mode have a five stop latitude and can handle a contrast ratio of only 32:1 before loss of detail occurs. Black and white and color negative film have a latitude of seven stops and can handle a contrast ratio of 128:1 (this can be greater with medium-format digital sensors). The human eye is capable of adjusting to a ratio in excess of 1000:1.
Rodrick Bond
Activity 2 Choose a capture medium (digital, transparency or negative film). Light a gray card with a diffuse light source; ensure the card fills the frame. De-focus the camera and take a reflected or incident meter reading. Either side of correct exposure, overexpose and underexpose in sequence one to five stops. Process the film or download the digital files and open in Adobe Photoshop. Evaluate and document the point at which the film or image sensor is unable to record detail above and below correct exposure (latitude). This indicates the capture medium’s latitude and its ability to handle incorrect exposure.
84
