MTF charts (short for Modulation Transfer Function) provide a graph analyzing a lens' ability to resolve sharp details in very fine sets of parallel lines, and a lens' contrast or ability to provide a sharp transfer between light and dark areas in sets of thicker parallel lines. Fine repeating line sets are created parallel to a diagonal line running from corner to corner of the 35mm frame, directly through the exact center of the image area. These are called sagittal lines, sometimes designated "S" on Canon's MTF charts. At a 90° angle to these, additional sets of repeating lines are drawn, called Meridional (or "M") line sets. Repeating extremely fine short parallel lines spaced at 30 lines per millimeter measure the lens' ability to record fine details, or its resolution.
MTF chart for the Canon 100-400mm f/4.5-5.6 L IS USM Lens
- The thick solid lines represent contrast of image
- The thin solid lines represent sharpness/ fine details of image
- The dashed lines represent bokeh characteristic etc. of image
- The more parallel are the lines the image quality is degrade less from center to corner. and
- The higher the position of the lines in the graphs the better is the image quality.