Origin of (1/Focal Length) guideline?

[ST1100]

Does anyone know where this rule of thumb originated?

Specifically, what assumptions have been made about the limits of handholding, image sharpness requirements, etc. i tried looking around the internet; everyone quotes the rule, but nobody seems to discuss it in depth. Any links will be much appreciated. TIA.

 

[clive]

i guess long ago some guy made detailed records of exposure settings for many different pictures he took ...and somehow noticed the correlation between focal length and shutter speed :think: thats how science progressed throughout the ages :bsmilie:

anyway the limits of hanholdability varies with individual..but can always be trained to be improves. below r some guidelines(slowest possible hand holding shutter speed limits) for fullframe 35mm slr:

20mm:1/4s
28mm: 1/8s
50mm: 1/20s
100mm:1/45s
200mm:1/90s
400mm:1/125s

cheerz