Converters are optical elements that allow focal points lenght increasement to wide or tele area. Converters main characteristic is expressed in number designation ?.?X which indicates whether it serves for increasement or decreasement of focal point lenght. Converters designated with less than 1.0X are wide converters (0,7X, 0,5X), and those designated with more than 1.0X are tele converters (1,4X, 2,0X). Final focal point lenght is attained by simply multiplying objective's basic focal point lenght with converter factor, so 100mm objective becomes 200mm with 2.0X converter, i.e. 50mm with 0.5X converter. Of course, this feature has its price, and that is lower photography quality and objective's lower light bandwith because of more optical elements.

X 1,4 low end teleconverter