Design and experimental validation of novel optics-based autofocusing microscope

Precise autofocusing microscope with rapid response

“…As shown, if the initial defocus distance δ 1 is located outside of this linear range, the autofocusing procedure should commence by shifting the objective lens through a distance L, where L is equivalent to half the linear range. If the resulting defocus distance δ 2 is still located outside the linear range, the objective lens should be shifted through a further displacement L. This procedure is repeated until the defocus distance (e.g., δ 3 ) falls within the linear range, at which point the objective lens can be moved directly to the point of maximum focus [4]. Therefore, the focusing response time of the autofocusing microscope depends on the linear curve of its motion characteristics and the number of times the objective lens is shifted.…”

“…1 presents a schematic illustration of the optical path within a conventional optics-based autofocusing microscope. It has been shown that if the image intensity remains constant over the entire sensor image, a linear relationship exists between the centroid of the image captured by the CCD sensor and the defocus distance, δ. Exploiting this linear relationship, an autofocusing capability can be achieved by driving the objective lens using a position feedback signal based on the centroid coordinates of the detected image [4,23]. Fig.…”

“…As a result, many sophisticated autofocusing schemes have been proposed in recent decades. As discussed in [4], existing autofocusing microscopes can be broadly classified as either image-based (i.e., software) or optics-based (i.e., hardware). Image-based or software autofocusing microscope is based on the image sharpness identification or the image spatial frequency function [5].…”

A High Precision Laser-Based Autofocus Method Using Biased Image Plane for Microscopy

“…Distinguished from the image-based methods, opticbased autofocus methods adopt auxiliary optical paths for defocus detection, which have also been widely researched [6][7][8][9][10][11]. Hsu's team developed a laser-based autofocus system that had fast response characteristics [6].…”

“…Liu et al [8][9][10][11] proposed a laser-based autofocusing method using geometric optics to achieve fast and precise autofocus performance. In Liu et al's method, a knife was used to bisect the detecting laser beam for bidirectional defocus detection.…”