Centered Camera Problem

class GameScene: SKScene {
override func didMoveToView(view: SKView) {
/*
        // This is the problem code
        let cam = SKCameraNode()
        cam.position = CGPoint(x: self.frame.midX, y: self.frame.midY)
        self.camera = cam
        self.addChild(cam)
*/
        let sprite = SKSpriteNode(imageNamed:"Spaceship")
        sprite.xScale = 0.5
        sprite.yScale = 0.5
        sprite.position = CGPoint(x: self.frame.midX, y: self.frame.midY)
        self.addChild(sprite)

    }
}