Abstract

A random target method for fast MTF inspection is proposed. The setup includes a random target, lens under test and a CCD camera with focus adjustment. The target consists of a random black and white pattern of a flat spectrum. The MTF of the lens is acquired by imaging the random target on the CCD using the lens under test, and then analyzing the spatial frequency content of the image. Frequency range up to about 50 cycles/mm is possible using commonly available CCD imagers. Measurement speed and precision depend on the sample matrix size used in calculation. A matrix of 128*128 samples per measured field point provides better than 2% precision and a few second’s total execution time (ordinary PC-computer) per lens including best focus evaluation and the measurement of tangential and sagittal MTF curves of 5 field points. Thus fast MTF inspection of low to medium quality lenses seems possible.

© 2004 Optical Society of America

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References

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    [CrossRef]
  2. A. Daniels, G. Boreman, A. Ducharme and E. Sair, �??Random transparency targets for modulation transfer measurement in the visible and infrared regions,�?? Opt. Eng. 34, 860-868 (1995).
    [CrossRef]
  3. E. Levy, D. Peles, M. Opher-Lipson and S.G. Lipson, �??Modulation transfer function of a lens with a random target method,�?? Appl. Opt. 38, 679-683 (1999).
    [CrossRef]
  4. E.C. Ifeachor and B.W. Jervis, Digital signal processing (Prentice Hall, 2002), Ch. 3.
  5. Sine Patterns LLC, 3800 Monroe Avenue, Pittsford, NY 14534, USA.

Appl. Opt.

J. Opt. Soc. Am.

Opt. Eng.

A. Daniels, G. Boreman, A. Ducharme and E. Sair, �??Random transparency targets for modulation transfer measurement in the visible and infrared regions,�?? Opt. Eng. 34, 860-868 (1995).
[CrossRef]

Other

E.C. Ifeachor and B.W. Jervis, Digital signal processing (Prentice Hall, 2002), Ch. 3.

Sine Patterns LLC, 3800 Monroe Avenue, Pittsford, NY 14534, USA.

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Figures (5)

Fig. 1.
Fig. 1.

Flowchart of the algorithm and a basic sample matrix geometry including five field points.

Fig. 2.
Fig. 2.

Simulated MTF results.

Fig. 3.
Fig. 3.

Instrument setup.

Fig. 4.
Fig. 4.

Lens-camera MTF measured with random target and single frequency methods.

Fig. 5.
Fig. 5.

Precision of the random target method as a function of frequency and sample matrix size

Equations (7)

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MTF = ( A max A min ) ( A max + A min ) ,
f max = 1 ( 2 l ) ,
l = ( h * M ) N .
PSD image = MTF total 2 * PSD t arg et ,
MTF total = MTF sys MTF LUT .
MTF LUT = ( PSD image PSD t arg et ) 1 2 MTF sys ,
PSD image = PSD measured PSD sys .

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