For such scenario, we can use the Modal Navigation instead of using pop up. This approach conforms with the standard navigation that is commonly found in modern mobile apps. For more detail, please check the Standard Navigation article.

My Inventory sample is a good place to start.

this.AddBinding("TableView", BindableProperties.DetailNavigationTargetProperty,  new NavigationTarget(typeof(ItemEditorViewModel), new NavigationParameter(){Animated = false, NavigationMode = NavigationMode.Modal, EnsureNavigationContext = true}), true);

The above code can be used as the custom navigation to show Modal Navigation with no animation. The code should be implemented in ItemListBindingProvider.cs. Next, we should do the following:

1. Add the view model for the view controller that will host the image view;
2. Create the view for the view controller using XIB definition;
3. Set the outlet for the ImageView using Xcode;
4. Define a binding provider for the view controller that sets the ImageSourceProperty to the ImageView;
   this.AddBinding("MyImageView", BindableProperties.ImageSourceProperty, "Item.Image", BindingMode.TwoWay);
   Don't forget to set the Item property in the view model in the navigated event of the view model.
   this.Item = parameter.Data as YourItem;
5. Bind the command property to the image view, so that the command in the view model is triggered.
   this.AddBinding("ImageView", BindableProperties.CommandProperty, "CloseImageCommand", BindingMode.TwoWay);
   The CloseImageCommand may contain this definition:
   //define in view model
   this.NavigationService.Close();
   This is to close the modal navigation.

Hope this helps.