Analog autofocus circuit design for scanning microscopy

Miguel E. Bravo-Zanoguera; Jeffrey H. Price M.D.

doi:10.1117/12.273647

2 May 1997 Analog autofocus circuit design for scanning microscopy

Miguel E. Bravo-Zanoguera, Jeffrey H. Price M.D.

Proceedings Volume 2982, Optical Diagnostics of Biological Fluids and Advanced Techniques in Analytical Cytology; (1997) https://doi.org/10.1117/12.273647
Event: BiOS '97, Part of Photonics West, 1997, San Jose, CA, United States

Abstract

The description of an analog autofocus circuit design, developed for a scanning microscope, is presented. The analog circuit measures the degree of focus directly from the video signal of the microscope CCD camera. The circuit then returns an index to the host computer for the purpose of adjusting the position of the objective lens to bring the object in focus. Best focus is found by comparing indices at several different vertical positions. The criterion adopted for determining the degree of focus is derived from the energy distribution of the video signal spectrum. The high frequency energy of the video spectrum is a maximum at best focus and as the optics defocus, the distribution shifts to lower frequencies. A previous digital autofocus implementation required dedicated real time image processing hardware. Real time autofocus is an order of magnitude less expensive with the analog circuitry described here than it was with the dedicated digital pipeline image processing. The characteristics of the analog design and its performance are compared to that of the previous digital implementation.

Citation Download Citation

Miguel E. Bravo-Zanoguera and Jeffrey H. Price M.D. "Analog autofocus circuit design for scanning microscopy", Proc. SPIE 2982, Optical Diagnostics of Biological Fluids and Advanced Techniques in Analytical Cytology, (2 May 1997); https://doi.org/10.1117/12.273647

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KEYWORDS

Analog electronics

Video

Microscopy

Microscopes

Phase contrast

Digital filtering

Optical filters

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