User's Guide

75
What is an Ev? What is a stop?
Ev stands for exposure value. The term stop comes from the name of aperture plates used in early
lenses. A change of one Ev or one stop will adjust the exposure calculated by the camera by a factor
of two.
Change in Ev Change in stops Adjustment to exposure
+2.0 Ev
+1.0 Ev
0.0 Ev
–1.0 Ev
–2.0 Ev
+2 stops
+1 stop
–1 stop
–2 stops
4X as much light
2X as much light
1/2 as much light
1/4 as much light
How much the exposure can be adjusted using
exposure compensation or manual exposure
before there is a loss of image quality depends
on subject contrast. High-contrast subjects have
a great range of tones, deep shadows and bril-
liant highlights, whereas low-contrast subjects
have a limited tonal range,such as a landscape
on an overcast day.
High-contrast subjects have a much narrower
exposure latitude before the shadows block up
from underexposure or the highlights washout
from overexposure. To ensure the best possible
exposure for a subject, brackets (p. 46) can be
made. Some scenes are beyond the contrast
range of the CCD. In those situations, expose for
the main subject of the image.
Calculated exposure
Exposure latitude
Decreasing exposure
Increasing exposure
Low-contrast subject
High-contrast subject