Probably very similar to what you already have.
First you'd want to combine the two images so each image shows half their current image. Then have a background map that you scroll (this could be done a few ways, but if you are using plugins, something similar to Map Zoom, except for a specific view).
You could potentially have three of the same image at different sizes, say x5 size for the scope views and x1 for the star map. Tile each image horizontally and use alpha masks or something similar to hide the parts of each image that shouldn't show.
Set it so that each image is moved at the same time instead of just one.
Have the horizon lens's and star map's Y sensitivities to 0 (You don't want either really moving in the y directions) and the star map's sensitivity to 0.2 for X. This way, when you move 5 px on the 5x larger (zoomed in) maps, you move 1 px on the smaller (zoomed out) map.
