I picked up Asahi Pentax SMC 17mm Fisheye (introduced 1975) before I left for my tour of the world. This lens is great for traveling because its extremely compact and built like a tank. It’s optics are superior and it captures a 180º impression of the world on a full sensor DSLR or 35mm film camera—not to mention that analog lenses just look and feel rad. I scored the lens on eBay for $200...