16-35 vs 17-35 vs 24 1.4 @ 24mm f8
At F/8, you'll be fine in terms of center sharpness with any of the lenses. What you might want to consider is the contrast, rendering, and flare resistance differences - things that are more subjective, along with, quite importantly, the focus distance to your subject - it's here where the lenses behave differently, and thus, where you might need to evaluate what you shoot.
Briefly, for landscape use, at 24mm, I'd recommend the following as options. In cases where I've not (yet) shot the lens, I'm going from opinions from people I know personally who have - not just internet or fanboy chatter.
24/1.4G: well balanced between near, middle and far focus distances. Excellent contrast and color, good distortion control, sharp. Microcontrast is extended across all of frame. My own personal choice for landscape.
Zeiss 25/2: (Based upon what I'm hearing from those whose opinions I trust): Brilliantly excellent in the mid focus distance ranges, not so much at infinity. Center sharpness in the mid distances is insane, corner sharpness drops a touch. Contrast and color are excellent. If the subject matter is mid distances primarily, from what I'm hearing and what I've seen in samples, this is the lens of choice.
14-24/2.8G Zoom: World class at 14mm, very very good at 24mm. Very strong contrast and strong, but cool, color performance. Excellent distortion characteristics at 24mm - best of the bunch actually. Performs best in the close to mid focus distances, but is still very good at infinity. Gotta watch the flare from the sides, but better than you expect flare resistance when it's straight on.
24/3.5 PC-E: Based upon people I know who have shot it. Seems to be better at the close to mid distances - I've seen some comparisons where both the 14-24 and the 24/1.4G are slightly (by the tiniest amount) better at infinity. However, the tilt/shift capability is huge as it can help with DOF and keep you out of diffraction limited apertures. For those who do landscape exclusively, this is likely a must have.
The above four are what I'd say are your top tier 24 options. The next two are, IMO, a definite step down, although certainly quite good overall at 24mm
17-35/2.8 AFS: Older lens. Very sharp at 24mm and stopped down, but doesn't have the contrast and certainly not the microcontrast of the top tier lenses. Still very good though. Not as nice in the corners as the top tier glass though. Strongest in the 20-28mm range.
16-35/4 AFS: Wicked sharp at 24mm and infinity - at that specific length and distance combination, it's a stunner. Weaknesses are that it's not quite as good in the closer and mid distances as it is at infinity, and it's got some field curvature issues as well. Flares worse than you think - I'd actually take the 14-24 over this lens even for flare situations, believe it or not. Lousy at 35mm, pretty good at 16, strong range is 20-28mm, and distance. There is better stuff for up close. So it's a compromise lens - and if you use it where it's strong, you'll be happy. If you use it where it's not strong, you won't be happy. I think that's why you see so many varied opinions on it. I sold mine - I just prefer the 14-24 and 24/1.4G to this lens, but it's not a bad lens either.
Also consider the Zeiss 21/2.8 Distagon - one of the great landscape lenses of our era, and very much top tier.
Take my comments with grains of salt - particularly for those I've not shot. One should always look at the consensus view on lenses as opposed to listening to a solo voice. By doing so you will avoid being misled by folks with biases or things they want to sell you, fanboys, and folks who do not test properly across enough scenario (multiple distance, subjects, etc).
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