Abstract: A multichannel digital signal correlator or structurator receives pulses e.g. from a photo multiplier (1) and passes them through a standardizer into channels 1 to M. Each channel has a counter (5.sub.m, m=1 to M) and shift register (6.sub.m) together with a multiplier (7.sub.m) and accumulator (8.sub.m). Clock pulses are applied to each counter (9) and shift register (6.sub.m) from a clock (4) through frequency dividers (9.sub.m) each set to different values giving increasing sample times (T.sub.s) in successive channels. Each multiplier (7.sub.m) has one input to the first stage of its associated shift register (6.sub.m) and another input connected to the fourth stage of the shift register (6.sub.m). Thus the multipliers receive two inputs one delayed (by .tau.) with respect to the other input. Accumulators (10, 11) count the number of photomultiplier pulses and clock pulses respectively during an experimental run. The correlator thus correlates two signals with increasing sample times (T.sub.

Abstract: A digital signal processor has timing means for providing a succession of sample intervals in which incoming digital signals may have discrete values (e(o)). A serial delay such as a multi or single bit shift register progressively delays a digital signal giving a delayed signal (e(m)). An arithmetic section has a plurality of elements such as multi or single bit multipliers, or difference squares. Each element operates on non delayed signals (e(o)) and signals (e(m)) from an associated stage of the delay. An accumulating store has a plurality of channels each associated with and arithmetic element. Collectively the channels provide the required mathematical operation, e.g. auto or cross correlation function or structure function calculation. The interval of delay between channels is arranged to increase substantially geometrically e.g. by .sqroot.2. The overall delay increase may be variable and geometric although increases between adjacent channels may be approximations to a geometric increase.

Abstract: An imaging system for obtaining information within the diffraction limit comprises an illuminating source of radiation, e.g. a laser. A lens system focuses radiation from a small area of an object onto a detector array in an image plane. The detectors measure the amplitude of the received radiation giving a matrix of information. This matrix is then inverted by a computer to reconstruct the image for observation on a cathode ray tube. The object is scanned by scanning the radiation or stepping the object.

Abstract: Blood flow in a retinal blood vessel is measured by detecting the doppler shift imparted to two laser beams intersecting on a portion of the retinal vessel. Twin beams of laser radiation are directed along an optical path into an eye and scattered radiation returned along the path into two photo-multipliers. The twin beams are passed through a beam rotator so that the plane containing them can be aligned along the retinal vessel under measurement. A local oscillator signal for homodying with the doppler shifted laser radiation is obtained from reflections from the eye itself or a separate reflector. This reflector can be moved to impart a frequency shift to the local oscillator signal to remove ambiguities in the doppler measurements. Automatic tracking of small eye movements is provided by a beam deflector and servo motor controlled by a detector.

Abstract: Blood flow in retinal blood vessels is measured by directing laser radiation along an optical path into the eye and onto a blood vessel. Laser radiation reflected off moving blood corpuscles is directed back along the optical path and into a detector. This reflected laser radiation is mixed with a proportion of the original laser signal to determine the doppler shift produced by the moving blood corpuscles and hence blood velocity.