Good sign

Can't wait to see first Reviews, and for now I anticipate that Sigma Art may well beat Pentax standard zooms (all of them) in terms of
- bokeh,
- color richness,
- contrast, and
- lens flaring?
That's because I have been pointed towards an A/B comparison from the Canon community, which proves that a Sigma Art prime beats even an expensive Canon L counterpart pretty easily, in ALL of the above criteria. See e.g.
Sigma 50 Art Lens Compared With The Canon 50mm F1.2L - DIY Photography
That's an encouraging sign, isn't it? that may silence those Sigma cliches, which stem from Sigma's pre-Art past. Also with regards to coating (for color rendition, contrast, and lens flare robustness).
Weather sealing?
Hmmm. Never worried much in the past to be frank. Every lens I used could stand a good amount of raindrop hits anyway, also those not designated as "water proof" explicitly. None of my lenses ever became foggy inside or anything.
Should a heavy rainstorm (or just heavy rain) kick in, most of us pack up anyway (because most of us just hate working with wet front lens elements) (at least I do). Else I would pack out an umbrella, if I had to shoot under heavy rain. Whatever protects the front glas from becoming wet also protects the lens barrel. Wide angle zooms' lens hoods don't protect well enough, unless you shoot stritcly into the opposite direction to where the wind coming from. And you also better not shoot in cities then, where the shooting angle is often upwards for many buildings or any other motiv which is taller than you. Also, my "rainy" landscape / cityscape photos were dull and gray-ish. And were never really tack sharp, as rain seems to destroy some sharpness, if your motiv is further away.
Probably many share such thoughts, so that Sigma's market researchers found out about that, and consequently waived an explicit (= extra heavy duty) rain&thunderstorm sealing, even in the Art's price category.
'Fine art photography' (or even just ambitious photography) and 'rain' just don't go together really. Under rain, the motiv and picture quality is degraded so much from so many different aspects, that you could get away with your handy 18-55 WR zoom, without loosing out on anything. You even don't need extra bokeh, because the background would be mostly dull and gray anyway, i.e. already non-distracting even without much bokeh
Or just let it be. Go to 500px.com, confirm that the ratio between rainy and non-rainy shots is 1:1000000, draw your conclusion, and adopt this ratio as your personal ratio as well
Last edited by Frater; 06-27-2014 at 12:39 PM.