IOS it is in the lens
for photos that lens doesn't seem to bad especially with lots of light, but it's aweful slow..... the 12-35 does pretty good still and video
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vid
But, i recently bought a bunch of glass.... 14-140 similar speed to your op question, 100-300 and both those work bitchen on the ground. 100-300 is a bit much without a tripod, over 230ish i can't make clear with touching the camera to shoot.... 2:1 crop make sit pretty long. But, specifically for video and cinema i bought the Rokinon t2.2 16mm cinelens and the voightlander f.95 17.5mm and lemme tell ya, money. This was the voightlander
rokinon
I also have the 7-14 lumix but it's slow and we don't use it much unless we want to purposely get that affect like at sunrise, anything not lit gets black, sunrise pops harder, but that's about all i do with slow lenses anymore with video. mid day stuff they work alright, kids playing sports, capturing fishing, bright sunny stuff. under clouds, sucks, dawn/dusk, sucks. but photos where you can tweek the settings they do a lot better.... 7-14 photo
it has a trippy look, clean but weird, this was probably at 8-9mm if had to guess, it didn't have filters but that just changed so look forward to more flying this one wide with nd's
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This weekend were doing a demo with gh4 and i'll try getting these lenses in action on a set to see what they do..... that was my whole reason to go in on m43 lenses.
that rokinon is on sale at adorama for $499... one warning though, this rok is the heaviest m43 lens you will ever find. the voight is right behind it, but its size is normal, just metal cased. the rokinon is huge, 9-10" long 2-3 lbs