Melgar's article and photos in OGR are a must read. The article is very clear and beautifully written.
In case you folks didn't know, Melgar is a retired aerospace engineer who, among other things, worked on the Hubble Space Telescope, and taught aerospace engineering as a college professor.
He applies the same precision and skill to his modeling, photos, writing, and teaching of modeling as he did to his work as an aerospace engineer.
Arnold