Canon III-A User Manual download pdf (Page 15)

DEPTH OF FOCUS SCALE See Illustration below. A little study will show how to plan

the exposure you want. The Distance Scale and the Depth of Focus Scale are used together.

Index Mark

Knurld

Ring

Focusing Ring

Distance Scale

Distance Index Mark

Depth of Focus Scale

Depth of Focus means the range of objects

which will be in focus on your film. This range

varies with the distance of the object of sharp

focus and the Lens Aperture (see page 11).

It extends from in front of the object of sharp

focus to beyond it. The greater the Lens

Aperture, the less will be the Depth of Focus.

Depth of Focus also diminishes in proportion

to decrease in distance the object of sharp

focus is from the film plane.

The illustration shows the Lens Aperture at

f:1.8 and the Distance Scale at 25 feet. An

object at 25 ft is in sharp focus. The Depth of

Focus Scale shows that the nearest object also

in focus is approximately 21 feet and the

farthest object in focus is approximately 30

feet. If the Lens Aperture Scale is set at

fill the object in focus will extend from

12 feet to infinity (o>).

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Canon III-A User Manual Page 15