Modulation Transfer Function

As North America's leading supplier of off-the-shelf optics, Edmund Optics now offers MTF (Modulation Transfer Function) performance data for our standard and NIR achromats. The informative curves tell designers how well the lens is able to transfer object detail to the image plane (see detailed explanation below). Each of the curves has been generated utilizing state of the art modeling software and test equipment that reflects real-world manufacturing and performance results - not theoretical guesses provided by most catalog houses. Our large staff of Optical and Manufacturing Engineers is available to assist you with specific integration or custom requirements.

What is MTF?

When characterizing the resolution of an imaging lens, it is extremely useful to refer to the Modulation Transfer Function (MTF). The MTF of a lens is a measurement of its ability to transfer contrast at a particular resolution level from the object to the image (see Figure 1). In other words, MTF is a way to incorporate resolution and contrast into a single specification.

Figure 1 - Example of an MTF curve of one of our Achromatic doublets:

An easy way to interpret MTF results is to think of imaging a target with black and white lines (100% contrast). No lens (even theoretically perfect) at any resolution can fully transfer this contrast to the image because of the diffraction limit. In fact, as the line spacing is decreased (i.e. the frequency increases) on the target, it becomes increasingly difficult for the lens to efficiently transfer this contrast (see Figure 2). Therefore, as the frequency increases, the contrast of the image decreases.

Figure 2 - Effects of diffraction on the amount of contrast imaged as the frequency is increased:

An MTF graph plots the percentage of transferred contrast versus the frequency (cycles/mm) of the lines. A few things should be noted about our Achromat MTF Curves:

  • MTF (also known as Contrast or Modulation) is the image contrast expressed in terms of the object contrast (1 = white on black, 0 = gray on gray). To calculate the Percent Contrast at the desired resolution, multiply the MTF value by 100%. In other words, an MTF of 1 is equivalent to 100% contrast or white on black.
  • The data for each curve was calculated using Optical Research Associates' CODE V® design software.
  • The spatial frequency is expressed in terms of cycles (or line pairs) per millimeter. The inverse of this frequency yields the spacing of a line-pair (a cycle of one black bar and one white bar) in millimeters.
  • The "Nominal" MTF curve was generated using the standard prescription information that is available in optical design programs. This prescription information can also be found in our catalog and on our web site. The nominal MTF represents the best-case scenario and does not take into account manufacturing tolerances.
  • The "Toleranced" MTF curve was generated using not only the tolerances specified for each parameter but also with optical specifications (such as power and irregularity) that can be found only on our manufacturing prints. The toleranced MTF takes into consideration the variables of lens manufacturing and is the closest representation of real-world results.
  • The MTF values were calculated on-axis with each lens oriented in an Infinite/Finite conjugate solution. Light rays filled the entire clear aperture (refer to specification table for clear aperture values), to represent how customers are typically using the lenses, not just the center portion of the lens which would have resulted in better on-axis performance.

Measuring MTF

Edmund Industrial Optics has invested in an Optikos VideoMTF™ measurement system (pictured above) which has become essential in system integration and custom designing of multi-element imaging systems (such as CCD lenses). This MTF testing equipment enables characterization of the actual performance of both designed lenses and commercial lenses (whose optical prescription is not available to the public). As a result, precise integration - previously limited to lenses with known prescriptions - can now include commercial lenses.


For more information on MTF testing or on the Optikos VideoMTF™ measurement system, you can visit the Optikos website at http://www.optikos.com.