The fractional gradient doesn't have a perfect correlation with the print judgment speed either. All sensitometrically defined speeds are substitute methods for determining film speed. The reason why the fractional gradient method was chosen is because it had the closest agreement over the greatest range of conditions with the print judgment speed.
spread function for Delta X.jpg
Ever? Can you point to the specific quote?I double-checked the paper... Delta-X isn't exactly at the 0.3 Gradient, you don't claim that.