c'est pas une question bête, tu n'es pas le premier à faire ce constat. c'est spécifique à ce caillou

Canon EF-S 18-200mm f/3.5-5.6 IS Lens Review

The focal length labels above correspond to those marked on the lens (the 135mm-labeled shot was actually 140mm according to the EXIF data). As the focal lengths make large increases relative to the prior setting (2x from 24 to 50mm), the angle of view rapidly narrows - bringing the subject in closer. The relative increase declines at the longer focal lengths - and the rate of change slows. The lens does not physically extend as fast above 135mm and the net change in angle of view from 170 to 200mm is very small.