via the lens wrote:
It really depends on the look you want to achieve. If you want a vast, wide open look you need the wider aperture but you already have an 18mm, which is wider than the 24mm, so you can already achieve that look. If you want a more compressed look, you use the 135mm view. Unless the 24mm lens you are thinking of buying is a fixed lens or a very superior lens, I can see no reason to purchase it other than you just want to.
That's not completely accurate. The last image I posted was a panorama using a 100mm lens on a D800. It has that expansiveness without the extension distortion that is a necessary evil that comes with using a wide lens. You end up cropping the sky and foreground in most wide-ultra-wide shots anyway. In addition, I tend to go longer because they have much better corner to corner sharpness, and for landscape I would rarely use a fast aperture short lens anyway. However the Nikon 24 F1.4 is quite a lens with good to excellent sharpness, corner to corner, at F4 and smaller apertures. In certain situations it is the perfect lens, but not for that "expansive" look. My go to lenses for landscape are my 45mm and 85mm PC-E - which provide very useful tilt and shift.