I'm trying to duplicate the "slide up from the bottom" animation that [UIViewController presentModalViewController:animated:] performs but without calling it because I don't want a modal view.

The below core animation code comes very close but appears to be changing transparency values of the views during it. At the start of the animation you can partially see through the view sliding up. By the middle/end of the animation the view we are sliding over is fully transparent so we can see behind it. I'd like both to remain fully opaque during this animation.

Any ideas on how to stop transparency changes in this code or to otherwise get the "slide up animation" I am looking for without requiring a modal view?

UIViewController *nextViewController = [[UIViewController alloc] autorelease];
nextViewController.view.backgroundColor = [UIColor redColor];  
CATransition *animation = [CATransition animation];
animation.duration = 3.5;
animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut]; 
animation.type = kCATransitionPush;
animation.subtype = kCATransitionFromTop;  
[self.navigationController pushViewController:nextViewController animated:NO];
[self.navigationController.view.layer addAnimation:animation forKey:nil];