UIImageView not scaling image down when setting constraints manually - ios

Question

I have a UICollectionView inside of a UITableViewCell, and the CollectionView cells show images that a user stores in the app. When the user taps the cell, the image is presented full screen. So I created a UIViewController, added a UIScrollView to it for zooming, then added a UIImageView to the ScrollView. Everything works nicely until the user changes the orientation of the phone. When they change to landscape the view adjusts but the scrollview and image view do not adjust, and therefore just show on the left side of the screen; they seem to keep the same bounds. I tried to fix this by following apple's tech note using the pure layout approach and adding constraints. But when I do this, the image that is displayed is zoomed all the way in and I cannot get it to fit correctly. When I use an NSLog statement to determine the frames, they are all set to self.view.frame and therefore printout the size of the screen, but the image still shows at full size. Everything is created programmatically, no xib files.
I would love to avoid the constraints, but they seem necessary for the user to be able to see images correctly in landscape mode. I have tried setting the contentSize of the scrollview, setting clipsToBounds to YES and changing the contentMode but none of these things have any effect. Any help is greatly appreciated!
collectionView:didSelectItemAtIndexPath:
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{
NSDictionary *viewsDictionary;
//creating ViewController to be presented
UIViewController *fullImageView = [[UIViewController alloc] init];
fullImageView.view.userInteractionEnabled = YES;
fullImageView.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[[UIApplication sharedApplication] setStatusBarHidden:YES];
_selectedImageView = [[UIImageView alloc] initWithFrame:self.view.frame];
NSString *key = [self.viewItem.imageKeyArray objectAtIndex:indexPath.row];
_selectedImageView.image = [self.viewItem.itemImages objectForKey:key];
_selectedImageView.clipsToBounds = YES;
_selectedImageView.contentMode = UIViewContentModeScaleAspectFit;
_selectedImageView.translatesAutoresizingMaskIntoConstraints = NO;
UIScrollView *imageScrollView = [[UIScrollView alloc] initWithFrame:self.view.frame];
imageScrollView.delegate = self;
imageScrollView.minimumZoomScale = 1;
imageScrollView.maximumZoomScale = 2;
imageScrollView.translatesAutoresizingMaskIntoConstraints = NO;
[fullImageView.view addSubview:imageScrollView];
[imageScrollView addSubview:_selectedImageView];
viewsDictionary = NSDictionaryOfVariableBindings(imageScrollView, _selectedImageView);
[fullImageView.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|[imageScrollView]|" options:0 metrics: 0 views:viewsDictionary]];
[fullImageView.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:|[imageScrollView]|" options:0 metrics: 0 views:viewsDictionary]];
[imageScrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|[_selectedImageView]|" options:0 metrics: 0 views:viewsDictionary]];
[imageScrollView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:|[_selectedImageView]|" options:0 metrics: 0 views:viewsDictionary]];
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(dismissFullImageView)];
[fullImageView.view addGestureRecognizer:tap];
[self presentViewController:fullImageView animated:YES completion:nil];
}