sploo wrote in post #18128718
The look should be similar to what you'd get with the lens on a crop body - a lens isn't affected by the sensor that's behind it (i.e. it still projects the same image). I.e. a Sigma 18-35 f/1.8 on the 5D4 in 4K crop would look like a Sigma 18-35 f/1.8 on an APS-C body (albeit with just a bit more cropping).
The confusion over the cropping comes from how you calculate it. The 5D4 horizontal resolution is 6720 pixels. UHD is 3840, but DCI 4K is 4096 (see
https://en.wikipedia.org/wiki/4K_resolution
)
The 5D4 records 4K in the latter format, which is a 6720/4096=1.64x crop. If you further crop the video down to UHD width then it's 6720/3840=1.75x crop.
However, some people calculate based on the diagonal resolution, so there are further variations.
Doh!!
... yeah as far as my coment on vignette .. i understand how it works but for some reason thought of it the other way around when i posted ..
OK, i understand about the crop factor 1.7 vs 1.6, thanks for the explanation
anyway , as far as video , it is what it is ..whether you are a serious(aspiring) videographer or a video noob,amateur /hobbyist(insert myself here
) and are looking for the Full frame look, 4k, video assist tools etc.. and reasonbly portable ( run-n-gun style) ,, and want to stay with canon ,you couldnt help but hope and be excited that canon would take back its place in the video dlsr world , or atleast be a strong 2nd place.... and then be dissapointed ...
but anyway , i'm over it .. 
i have no choice , canon obviously has no interest in filling this area in ,, i guess the way they see it is , why bite into their cinema line cameras..if someone wants all that they ll buy a C series camera...
Fortunaly there are other options , mainly from Sony
and from M4/3 (,if you dont have to have FF and are ok with iso capabities)which have lenses that support theier 2X crop
thats the route i went ,, a7sii does Great video .. and still gives me decent stills
and holding on to the 5d3 for now , for when i need better than the a7sii's decent stills
like i said before i'll probably own the 5d4 some time early 2017 for its stills capabilities..
although the way you guys are raving about it , you all might push me to get it sooner than later