LENSES: Facts and Fallacies - Part V

[Gerald]

The article discusses here the veracity of the numbers engraved on lenses, and discovers that manufacturers often cheat.

The actual focal lengths of wide angle lenses are generally larger than the nominal. For example, the FL of the Pentacon 29mm F2.8 is more than 30mm. It seems that the manufacturer was a little embarrassed to mark the lens as 28mm and used the odd nominal focal length of 29mm. Likewise, the Zeiss Flektogon 20mm F2.8 is in fact a 21mm.

With telephoto lenses precisely the opposite happens. The actual focal distance is less than the nominal. My Sigma APO 400mm F5.6 seems to be somewhere around 380mm.





to be continued...