iMac hangs with edge sharpen use

Hello: Hoping someone can shed some light on a recent issue I'm having with the use of the edge sharpening brick

System: Late 2009 27" iMac 3.06 Corer 2 Duo, 10.8.2, Aperture 3.4.1. I recently upgraded both in the hopes that this would fix the problem with no luck.

Problem: Computer hangs or freezes with use of edge sharpening brick. Sometimes freezes completely (no cursor visible) & other times goes to spinning meatball. In all cases, system is hung which requires a POR to recover. I'm not sure if Force Quit would work as I just realized I've been doing it wrong - I'll try that next time it happens...When this occurs, I typically have the intensity control max'ed out (1.0) and am adjusting the edges control with pic in full screen, zoom mode with the loupe activated at 400%. This seems to happen about every 20 pics or so

When everything comes back up I'll repair the database per apple rec.

If it matters, my pics are raw files from a Canon 5DmkII.