The old zoom-routine was very simple but lead to unwanted and jagged edges especially during zooming in. The new aberrator uses special routines (bilinear filtering) to keep the zoomed images more smooth and therefore more realistic.
The example below shows 4.27 waves of coma (see Suiter p.321 (4th print)). The image on the left is from the current V2.53 Aberrator and the image on the right is the new algorithm. Although the new algorithm is more enlarged the image but still has a smoother appearance.