Mockup is an app for Mac OS X and also a free app for iOS. Both these will allow you to preview your designs, layouts, or any arbitrary images in layers from your Mac computer on any number of connected iOS devices at once. All data is transferred to your devices in lossless and pixel-perfect quality. You can then control your layout and layers’ position, rotation, opacity, retina mode, and so on. You will be also able to control all connected devices and modify their Statusbar, Keyboard presence or their Orientation.