This is a short test of the Letus Extreme with the Sigma 50mm - 500mm f4 - f6.3 zoom. At the tele end of the zoom range, the Extreme is presented with a lens aperture of f6.3 which is outside the limit before groundglass artifacts can be expected to appear. Artifacting is evident in the sky. This lens also provokes similar artifacting in the same circumstances on the P S Technik Mini35. Jandakot Airport is apparently the busiest general aviation airport in the Southern Hemisphere.