Canon 10 x 30 IS Manual page 18

Wide field of view, with superior image quality overall.
Uses a doublet field-flattener.
The image quality around the edges is a very important point
to look at when selecting binoculars. If binoculars with inferior
image quality are used for an extended period of time, the user
will tire easily and may even become sick. The IS series use
the world' s first doublet field-flattener lens (Fig. 9). This is
Canon' s exclusive optical design with two field-flattener lenses,
lenses which are normally reserved for high-grade binoculars.
By using two lenses, Canon has achieved a wide field of view
of 67˚ (12x36 IS, 15x50 IS ALL WEATHER, 18x50 IS ALL
WEATHER), with unrivaled sharpness.
Object lens
UD lens
Vari-angle prism
(Fig. 6)
You can enjoy the power and sharp image .
Roof prism
Direction of movement
of the eye lens
Eye lens (Right side:
Moves when adjusting
for sight differences
between the left and
right eyes)
Moves when adjusting
the focus
(Fig. 6)