This is my main wide-angle lens for architecture and landscape, and one of the best of the new G mount line. With a focal length of 23mm (18mm in 35mm format equivalent), this super wide-angle lens is optimal for shooting landscapes and architectural photography. With a 12 groups and 15 elements construction using two aspherical lenses, one super ED lens, and three ED lenses, this lens suppresses distortion despite being a super wide-angle lens with a 99.9° angle of view. Get the best deal for this lens from the link above.
FUJINON GF23mmF4 R LM WR Wide angle Lens (18mm in 35mm format equivalent)