This is a segue that does an iris animation like the iOS camera app. Note: The name cameraIris is private API and might lead to rejection!

IrisSegue.mm

@implementation IrisSegue

- (void)perform
{
	[self.sourceViewController presentViewController:self.destinationViewController animated:NO completion:^{
		// don't ask - it just works with two calls to dispatch_async
		dispatch_async(dispatch_get_main_queue(), ^{
			dispatch_async(dispatch_get_main_queue(), ^{
				NSString* shutterAnimationName = @"cameraIris";
				
				CATransition *shutterAnimation = [CATransition animation];
				[shutterAnimation setDuration:0.5];
				
				shutterAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
				[shutterAnimation setType:shutterAnimationName];
				[shutterAnimation setStartProgress:0.5];
				
				UIViewController* destination = self.destinationViewController;
				
				CALayer *cameraShutter = [[CALayer alloc]init];
				[cameraShutter setBounds:destination.view.layer.bounds];
				
				[destination.view.layer addSublayer:cameraShutter];
				[destination.view.layer addAnimation:shutterAnimation forKey:shutterAnimationName];
			});
		});
	}];
}

@end