24mm F1.4 DG HSM | A Refurbished

10 lines per millimeter measure the lens's contrast ability (red lines). Repeating fine parallel lines spaced at 30 lines per millimeter measure the lens's sharpness ability (green lines) when the aperture is wide open.

Diffraction MTF takes diffracted light at every aperture into account which is very close to actual image data. Geometrical MTF does not consider the diffraction quality of light, yet it tends to show higher values than actual image.

The red line illustrates how the lattice pattern will appear in the actual picture when any lens distortion is taken into account.

The image will be seen as expanded (barrel distortion) in negative values or will be seen as a recessed (pincushion distortion) in positive distortion values.

The horizontal axis shows the image height and the vertical axis shows the brightness of the image