For photographic lenses Id say go ahead and write an article at photographic lens and well just add links from lens and lens disambiguation Im assuming that youll want to write photographic lens from a more practical point of view and keep lens mostly as a theory of optics type article Alternately we could just make lens a disambiguation page and move the articles to lens optics and lens photography I dont have a strong preference although the first option is easier  As for rainbow I cant see anything wrong with the picture  what makes you think it is a fake It seems it was added by  BTW    Jan   UTC