Parece un objetivo sencillito, la mayor paste de su cuerpo sirve a modo de parasol y no he encontrado su fórmula óptica. Aqui dejo unos ejemplos de su uso.
Saludos.
(http://img211.imageshack.us/img211/5719/agfacolor.jpg)
1
(http://img443.imageshack.us/img443/3091/b01s.jpg)
2
(http://img12.imageshack.us/img12/4107/b02an.jpg)
3
(http://img202.imageshack.us/img202/3143/b03li.jpg)
4
(http://img571.imageshack.us/img571/8945/b04bi.jpg)
5
(http://img687.imageshack.us/img687/1764/b05xx.jpg)
6
(http://img203.imageshack.us/img203/7047/b06m.jpg)
7
(http://img827.imageshack.us/img827/7130/b07d.jpg)
8
(http://img196.imageshack.us/img196/7914/b08t.jpg)