The camera and lens are only two of many tools used by a photographer to create an image. That said, the Tonika 11-16mm lens is a good fit for your D5100. If you are savvy with manual focus, the Rokinon 14mm (with "chip") will work with either camera for an amazingly low price point. What lenses to you currently have? Chances are you have a capable lens, and your money would be better spend on lighting, tripod, editing software, calibrated monitor, tablet, etc., and most of all, training in architectural photography. Let me know if I can help.