Frequency domain velocity measurements and time domain velocity measurements are made using light from cells or other objects. An optical grating is used to modulate the light from an object so that it has a frequency proportional to the velocity of the object. Depending upon the embodiment, the pitch of the optical grating is uniform or varying. The modulated light is detected and various signal processing techniques, such as a Fast Fourier Transform function, are used to indicate the velocity of the object. Preferably, the velocity measured is applied in determining a timing signal employed for synchronization of an image of the object and an detector signal in an optical analysis system that uses a time delay integration detector to determine characteristics of the object in response to light from the object.