Patent ID: 7087877

Claim:
A method for automatically focusing a flow imaging system upon objects entrained in a flow of fluid introduced into the flow imaging system, the method comprising the steps of: (a) introducing a flow of fluid into the flow imaging system, the flow of fluid including objects entrained in the flow of fluid; (b) obtaining a first signal corresponding to light from the objects entrained in the flow of fluid that has been modulated by a first optical grating; (c) obtaining a second signal corresponding to light from the objects entrained in the flow of fluid that has been modulated by a second optical grating; (d) processing the first signal and the second signal to determine a direction in which a focus of the flow imaging system should be adjusted to improve the focus of the flow imaging system on the objects entrained in the flow of fluid; and (e) automatically changing the focus of the flow imaging system on the objects entrained in the flow of fluid in the direction determined by a predetermined amount.