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Proceedings Paper

Focal length assessment by self-imaging
Author(s): Myrian C. Tebaldi; Nestor A. Bolognini; Alberto A. Tagliaferri; Roberto Daniel Torroba
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Paper Abstract

Several classical and modern approaches were developed in the literature for measuring the focal length of a lens. We focus our attention on those that employ self-imaging methods. In our proposal, a collimated laser beam illuminates a test lens. After the lens, the wavefront becomes convergent or divergent according to the lens power. Attached to the lens, we place a Ronchi grating. This procedure gives rise to several classical Talbot images, although magnified due to the non-parallel illumination. Key to our presentation is the use of the property that the pitch of each self-image is directly related to the focal length of the collimating lens. To obtain the pitches, a lensless CCD camera is positioned in any two consecutive self-images planes. The respective images are captured and processed. We designed software that allows first to precisely focus each self-image plane by a best-contrast algorithm, and then takes an intensity histogram along a direction perpendicular to the grating lines. By measuring the distance between consecutive self-image planes and their pitches, the focal length is determined. This method provides a reference testing with higher setting sensitivity and an increase in the accuracy compared to previous methods. Note that the proposed method represents a practical improvement over other existing methods.

Paper Details

Date Published: 21 October 2004
PDF: 5 pages
Proc. SPIE 5622, 5th Iberoamerican Meeting on Optics and 8th Latin American Meeting on Optics, Lasers, and Their Applications, (21 October 2004);
Show Author Affiliations
Myrian C. Tebaldi, CIOp (Argentina)
Univ. Nacional de La Plata (Argentina)
Nestor A. Bolognini, CIOp (Argentina)
Univ. Nacional de La Plata (Argentina)
Alberto A. Tagliaferri, Univ. do Estado do Rio de Janeiro (Brazil)
Roberto Daniel Torroba, CIOp (Argentina)
Univ. Nacional de La Plata (Argentina)

Published in SPIE Proceedings Vol. 5622:
5th Iberoamerican Meeting on Optics and 8th Latin American Meeting on Optics, Lasers, and Their Applications
Aristides Marcano O.; Jose Luis Paz, Editor(s)

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