It's that time again when I am anxious for a new lens. Normally this is an easy decision, but this time around I am looking at getting an ultrawide angle lens. Currently my widest lens is the 24-105L on my 5dIII. For reference I've never actually shot with anything wider (just the equivalent angle of view from a 7d and 15-85) so I'm looking to break new personal ground here! Part of the motivation and timing for this upgrade is that we are planning another vacation in January (San Francisco, Maui, Kauai, LA and Orlando) and I thought it would be nice to have something wider than 24mm for some different perspective and wide landscape shots (keep in mind that I've never shot with an UWA so I'm just going based on other's examples).

I've been leaning towards the canon 16-35L II, mostly because I thought this was the "best" option. I also thought the 2.8 appeture would be helpful and would also hopefully enable some "starscape" and night shots which I would like to try (tried a couple with the 24-105 and quickly realized that a wider angle of view and faster glass would definately help). I'm not sure how the 16-35 performs for star shots though and whether this would be a good use for this lens.

Thinking about night star shots led me to read some reviews on the samyang/rokinon/bower 14mm 2.8. I understand this is manual focus and appeture control so that would be quite different, but I understand the IQ is quite good (except some odd distortion) and it seems to be well used for starscapes. My hesitation here is the full manual controls (focus especially) and whether it would be truly useful for anything other than starscapes. Would I really use a lens this wide for landscapes (especially since composition seems to get more difficult with wider angles)? Would I miss the versatility of the zoom? Price is definately a nice thing about this lens though... Anyone use this lens and have any input here?

And then there is the canon 17-40 L. Seems like this would be great for landscapes (and cheaper than the 16-35), but I'm not sure f-4 would be fast enough to use for any starscapes. Otherwise I like the smaller size and cost and the IQ seems to be on-par with the 16-35 once you stop down a bit. But I'm not sure whether I would miss the faster 2.8 appeture of the other two lenses.

The canon 14mm prime seems overpriced to me for my anticipated usage, so I haven't really considered that.

A bit of rambling, but I'm really just trying to think-out-loud on what decision to make here. Cost is certainly a factor, but I can manage either of the lenses (or possibly the 17-40 and samyang 14). I guess it is mainly comes down to whether I need the 2.8 appeture, which I really don't know.... Maybe I'm basing this too much on the possibility of using this for starscapes (which I would like to try, but I'm not sure it is worth spending a considerable amount of money without even really trying it out first).

Any input or suggestions to sort out my rambling decision is welcome!

Stephen