アスペクト比（幅を高さで割った値）。
By default the aspect ratio is automatically calculated from the screen's aspect ratio, even if the camera
is not rendering to full area.
If you modify the aspect ratio of the camera, the value will stay until you call camera.ResetAspect();
which resets the aspect to the screen's aspect ratio.
関連項目: Camera コンポーネント、Screen クラス .