The modulation transfer function of a display oscilloscope: measurements and comments

Area of Science:

• Optics and Display Technology
• Instrumentation and Measurement

Background:

• Oscilloscope "spot size" is often defined at half peak amplitude, not total light distribution width.
• The modulation transfer function (MTF) of displays can significantly affect perceived stimulus contrast, particularly with short viewing distances.

Purpose of the Study:

• To measure spot profiles of a typical high-resolution oscilloscope display.
• To derive the modulation transfer function (MTF) of the oscilloscope instrument.
• To present a correction method for determining actual sine wave grating contrast from manufacturer spot size specifications.

Main Methods:

• Measurement of spot profiles on a representative oscilloscope display.
• Calculation of the display's modulation transfer function (MTF) from spot profile data.
• Development of a correction algorithm for contrast calculation.

Main Results:

• Spot size characterization at half peak amplitude was performed.
• The MTF of the oscilloscope display was derived, quantifying its contrast transfer properties.
• A practical method for correcting stimulus contrast based on spot size was established.

Conclusions:

• The definition of "spot size" on oscilloscopes requires careful consideration regarding its impact on contrast measurements.
• Understanding and quantifying the display's MTF is crucial for accurate stimulus contrast assessment.
• The proposed correction method allows for more precise determination of sine wave grating contrast.