How to change SCNView pivot point - swift

Question

Question
How does the SceneView/camera work out around which point to rotate, and how do I force the scene to rotate around the red sphere (-2, 0, 0)?
Demo
In this example SceneView I have placed
a camera at (-2, 0, 5)
a red sphere at (-2, 0, 0)
a blue sphere at (-1, 0, 0)
a white sphere at (0, 0, 0)
So the camera is in the same position along the x-axis as the red sphere
In the image you see the scene rotates around the blue sphere.
Playground example
Here is a working playground to produce the above example
import UIKit
import SceneKit
import PlaygroundSupport
var scene = SCNScene()
var sceneView: SCNView = {
let s = SCNView(
frame: CGRect(x: 0, y: 0, width: 600, height: 600)
)
s.scene = scene
s.backgroundColor = UIColor.black
s.allowsCameraControl = true
return s
}()
PlaygroundPage.current.liveView = sceneView
let redXPosition: simd_float1 = -2.0
let blueXPosition: simd_float1 = -1.0
let originXPosition: simd_float1 = 0.0
// MARK: Scene Nodes
let cameraNode: SCNNode = {
let n = SCNNode()
n.camera = SCNCamera()
n.camera?.contrast = 0.0
n.camera?.wantsHDR = false
return n
}()
cameraNode.simdPosition = simd_float3(redXPosition, 0, 5)
scene.rootNode.addChildNode(cameraNode)
let ambientLightNode: SCNNode = {
let n = SCNNode()
n.light = SCNLight()
n.light!.type = SCNLight.LightType.ambient
n.light!.color = UIColor(white: 0.75, alpha: 1.0)
return n
}()
ambientLightNode.simdPosition = simd_float3(0,5,0)
scene.rootNode.addChildNode(ambientLightNode)
// MARK: Spheres
// MARK: Origin - White
let originNode: SCNNode = {
let sphere = SCNSphere(radius: 0.5)
let node = SCNNode(geometry: sphere)
let mat = SCNMaterial()
mat.diffuse.contents = UIColor.white
sphere.materials = [mat]
return node
}()
// MARK: Red
let redNode: SCNNode = {
let sphere = SCNSphere(radius: 0.3)
let node = SCNNode(geometry: sphere)
let mat = SCNMaterial()
mat.diffuse.contents = UIColor.red
sphere.materials = [mat]
return node
}()
// MARK: Blue
let blueNode: SCNNode = {
let sphere = SCNSphere(radius: 0.3)
let node = SCNNode(geometry: sphere)
let mat = SCNMaterial()
mat.diffuse.contents = UIColor.blue
sphere.materials = [mat]
return node
}()
// MARK: Place nodes in scene
originNode.simdPosition = simd_float3(originXPosition,0,0)
redNode.simdPosition = simd_float3(redXPosition,0,0)
blueNode.simdPosition = simd_float3(blueXPosition,0,0)
scene.rootNode.addChildNode(originNode)
scene.rootNode.addChildNode(redNode)
scene.rootNode.addChildNode(blueNode)