Lesson 3 : 1.3.2010 - Exposures

Lesson 3 : 1.3.2010 - Exposures

Today's lesson taught as a more indepth understanding of exposure as well as how to calculate different apertures and shutter speedsin certain situations.

In-camera exposure calculation

Exposure = Total amount of light used to create an image. This is controlled by shutter speed and lens aperture . The same amount of exposure can be achieved using a variety of combinations

Exposure
The exposure used in any given situations is dependant on the following major factors.

- The ISO setting (film/sensor sensitivity)
- The lighting (level of subject illumination)
- The subject (level of subject reflectance)
- Personal preference

Origins in film sensitivity ratings

film with high sensitivity to light has a high rating
film with low sensitivity to light has a low rating

DIN (Deutsches Institut für Normung)
ASA (American Standards Association)
ISO (International Standards Organisation)

- High level of illumination allows the use of faster shutter speeds and smaller lens apertures

- Low level of illumination allows the use of slower shutter speeds and wider lens apertures and may also require the use of a tripod.

Camera uses a reflected exposure meter

measures light reflected from the subject
calibrated to ALWAYS render the subject as a MID-TONE
auto or manual results in same rendering
white subject = mid tone rendering
mid-tone subject = mid tone rendering
black subject = mid tone rendering
MANUAL exposure measurement allows you to adjust this rendering.

In Camera Exposure Modes
Average - entire field of view is averaged
Evaluative - interprets scene based on data base
Centre Wweighted - majority of measurement in centre
Spot - majority of measurement in small area