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Modulation Transfer Function

Section Overview:

The modulation transfer function (MTF) is a measurement of the microscope's ability to transfer contrast from the specimen to the intermediate image plane at a specific resolution. Computation of the modulation transfer function is a mechanism that is often utilized by optical manufacturers to incorporate resolution and contrast data into a single specification. Measurements of the relative modulation is useful for characterizing not only traditional optical systems, but also photonic systems such as analog and digital video cameras, image intensifiers, and film scanners.

Review Articles

Basic Concepts

Modulation of the output signal, the intensity of light waves forming an image of the specimen, corresponds to the formation of image contrast in microscopy. Therefore, a measurement of the MTF for a particular optical microscope can be obtained from the contrast generated by periodic lines or spacing present in a specimen that result from sinusoidal intensities in the image that vary as a function of spatial frequency. Topics covered in this section also include the optical transfer function, phase transfer function, and the contrast transfer function, all of which play a crucial role in resolution and contrast.

Interactive Tutorials

  • Diffraction Effects on Image Contrast

    Utilize a periodic line grating as the specimen and simulates images produced with a diffraction-limited optical microscope as a function of spatial frequency in this featured tutorial.

  • Cutoff Frequency and Airy Disk Size

    Explore the changes in the point spread function distribution as the spatial frequency cutoff is varied in a typical modulation transfer function plot in the featured tutorial.

  • Numerical Aperture Effects

    Examine the effect of microscope objective and condenser numerical aperture size on the relative modulation as a function of specimen spatial frequency in this interactive tutorial.

  • Test Target Intensity Scans

    The interactive java tutorial demonstrates intensity scans made from images of the periodic lines present on the MBL-NNF test target measured with a plan apochromatic objective.

  • Periodic Diffraction Images

    Examine periodic object produced diffraction images at several focal depths in this featured interactive tutorial. The periodic object featured in this tutorial is a Siemens test star.

  • Contrast Enhancement Technique MTF Curves

    Explore the effects of popular contrast modes on image contrast and the modulation transfer function of the modified microscope in this interactive tutorial.

Selected Literature References

Selected Literature References

The reference materials listed in this section are an excellent source of information on the modulation transfer function, contrast transfer function, and optical transfer function as applied to microscopes and other optical systems, video systems, and photographic film.

Contributing Authors

Mortimer Abramowitz - Olympus America, Inc., Two Corporate Center Drive., Melville, New York, 11747.

Kenneth R. Spring - Scientific Consultant, Lusby, Maryland, 20657.

John C. Long, Matthew Parry-Hill, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.

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