The 8-16 is addictive! it's wiiiiiiiiidddddddeeeeeeeeeeee VERY wide.
My always around kit is composed of my lighting kit (3 flashes,stands,umbrellas...one whole backpack, a big one, for it that i carry always, everywhere...spent an afternoon walking in the mountains with it the other day:P) and the sigma 8-16...i always carry my tammy 28-75, but i do not use it so often. Even my portraits are made with the sigma now. In the center it's sharp, the edges it deforms a bit and is not so sharp, it's slow (usually you have to use it at f8 to produce fine results)...but once you pair it with flashes that does not matter and all you feel is the inmense fun
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A lens like this is unique...and it's got drawbacks...the price you pay for the 8mm it boasts.
And between the sigma 85 and the 77 limited...i think i would go limited.
Good luck with this mad driving task you have! (the limiteds make a nice compact pack that'll be hard to beat).
Oh and about manual flash and shows you're absolutely right...too fast...you can always get a Metz af58...and still get pttl,auto and manual...Flashes are the best bang for the buck, they'll let you use all your lenses at their sweet spot for much less than a top-notch lens. And once you get into manual it's a delight
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