Changing the origin of the screen to allow for some effects

-- Create the parent group
local parentGroup = display.newGroup()
sceneGroup:insert( parentGroup )
parentGroup.x = math.floor( display.contentWidth / 2 )
parentGroup.y = math.floor( display.contentHeight / 2 )

-- Create the child group
local childGroup = display.newGroup()
parentGroup:insert( childGroup )
childGroup.x = -parentGroup.x
childGroup.y = -parentGroup.y

-- Now insert your game group into the child
childGroup:insert( yourGameGroup )

-- Now manipulate childGroup directly, eg xScale, rotation...