Originally posted by Marc Sabatella My assumption is the the aspect of focal length that matters to an SR system is field of view, so it can calculate the effect on the image of a given amount of angular motion. So I'd enter whatever focal length seems to best represent the field of view. .......

The relationship I gave earlier involving focal length and magnification in effect contains field of view in the form of focal length; the magnification factor is related to how far the sensor is from the lens, or the mathematical equivalent how far the subject is from the camera.

Lens_subject_distance=F(1+1/m)

Lens_sensor_distance=F(1+m)

The angular motion of the camera times the length from the sensor to the lens must be less than one viewing pixel (Circle_of_confusion) to avoid image smear. The angle is (rate)x(time)

(rate)x(time)xF(1+m) < Circle_of_confusion

time < (Circle_of_confusion/rate)/(F(1+m))

This is the basis of the shutter speed correlation with 1/F.

Iowa Dave