Originally posted by slip I am in the school of thought that no matter what the original focal length is, when ever you increase the length of something, the motion is going to increase at the one end due to the law of physics. If anyone has taken an ocean cruise would know how the bottom of the boat sways a lot less than the top
@SLIP is exactly right. In fact using the lens' true focal length for SR for anything other than infinity focus is incorrect.
Shake.Reduction.Focal.length = f(1+m) = f(1+sensor.width/scene.width)
Ignoring subject distance for SR gives a
fractional error = sensor.width/scene.width
for example with an asp-c camera, using an uncorrected focal length for a subject 10 feet from the camera results in a shake reduction error of about 1"/120" ~ 0.8%.
Dave in Iowa