Another suggestion would be to do the composite effect outside of Carrara. While Carrara is a very powerful tool, there are other tools that are more suited to what you're trying to do. You could pull off an old-style fade out (remember "the Enterprise Incident" from the old series) by rendering the animation without the cloaked ship present up to 15 frames after the ship is supposed to appear. Then, render the animation with the ship in place from 15 frames before the end of the first render. Overlap the two in a video editing package (Premiere, Video Wave, whatever), use the dissolve feature, and poof! you have a ship dissolving into view. Hope this is helpful. - Dex