Shot under a heavily light polluted sky, Visual Limiting Magnitude around 3.5, hence I used an Astronomik UHC filter (passes H-beta+OIII in Blue/Green and H-alpha+SII in Red). Unfortunately the stock 1Ds has very poor sensitivity to H-alpha (like for human vision), so even with the rather long integration time I was still unable to bring out the southern loop of M42. 11 five-minute frames stacked, augmented by a bunch of 2-minute and 10-second frames to fill in the Trapezium. A 1:1 Trapezium crop from a 10-second frame is inset. As can be appreciated, image quality is determined more by the quality of the tracking rather than the lens, even in the 10second frame. Shot at 840mm/5.6 (i.e. wide open). CGE Mount, autoguided by SBIG 237.