An humble size comparison between standard focal lenghts

50mm focal length lenses for 24x36mm sensor camera are said to be standard because if you open the eye that is not watching the viewfinder, both images coming from each eye are very closed. 50mm for 24x36mm sensors are equivalent in term of angles to 35mm focal length for APS-C sensors.

In the image above, which is more or less respecting the relative size between cameras, we can see that:

1) the lens for full frame is much bigger that others (it is generally the case but not always)

2) the absence of auto-focus (voigtländer lenses) yields smaller lenses

3) the bigger the maximum aperture is, the biggest are the lenses