Bresser NATIONAL GEOGRAPHIC 9057000 Mode D'emploi page 12

To fasten the main tube in the desired position, turn
the fastening screw (7) clockwise.
• Indoor versus outdoor:
Although you may casually observe through an open
or closed window, observing outdoors ensures op-
timal viewing conditions. Temperature differences
between indoor and outdoor air and the low quality
of window glass can blur images seen through the
spotting scope.
• Sun shield:
Extend the sun shield (8) when strong sun-
shine affects your visibility. Put your hand
around the spotting scope aperture ring and
simply push the shield out. But you should never
look at or near the sun! To find out more, read the
warnings in this manual.
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Observing land objects
When viewing objects on land, you will be observing
through air with varying levels of refractivity due to
varying air temperatures. This phenomenon causes
things to look wavy, causing a loss of image quality.
You may have noticed this phenomenon when driv-
ing down a highway on a hot day.
If this optical phenomenon interferes with your
viewing, try focusing at low power to see a steadier,
higher-quality image. Also, try observing in the early
morning, when air temperature is relatively uniform.