The PSF and especially the MTF are important function to describe a telescopes quality. The PSF is in fact only a slice of the values that appear on the X-axis (Y=0) and on the Y-axis (X=0) of the generated star-image.

The MTF is far more important since it shows the effects of aberrations in terms of losses at different resolutions. The x-axis shows the resolutions from large (left) to the theoretical finest details (size of the airy-disc) a telescope can show. The black line from the left-top to right-bottom shows a perfect telescope of the same aperture but without any aberrations and obstructions.

To use this function put a checkmark in the checkbox above the calculate-button on the right. Be aware that calculating a MTF adds a substantiai amount of computing to the routines.

In the above example a perfect SCT with a 30% obstruction was calculated with no additional defects. Notice the fact that this scope performs slightly (probably not noticable) better on finer details than a perfect refractor of the same aperture.