One more thing about the distortion(inherent in the
lens) in the original image, on how it's bowed, and produces the raised/humped image.
Look very closely and you should notice that it's not just a straight barrel distortion issue, it's more of a moustache distortion issue.
Moustache distortion, as the name implies, renders the straight line (of the water here) with a more complex line shaped like a comic moustache shape.
Curved centre, but then a slight dip in the middle sections of the left and right periphery, and then as you follow the supposed horizon out to the far edges(on each side) the curve then dips low again half way out to the edge from the centre and back up at the very edges.
eg. lets say that the first image is about 30cm across in length. in the centre is the raised hump, on either side of this centre about 20cm on either side, you notice a down slope/dip in the horizon line, and then further out from that ~20cm to the 28-30cm mark(again on each side) it bend back upwards again ... so the rendering is like a Mexican moustache shape .. ie. moustache distortion.
Straight up barrel distortion is just a typical raised centre with a simple radial bend downwards towards each edge.
Simple barrel is easy to correct for, but moustache is much harder and needs more specialised software to correct for the shape.
I know of, but never used, the type of software that allows you to make more complex adjustments(and can't think of the exact names of products right this moment), but some software use
lens profiles.
The
lens profiles have been set in the software to bend the complex distortions(like moustache) more accurately.
So, you're using Adobe software and you need to use a
lens correction profile that is specific to the
lens you're using.
With most
lenses from thirdparty manufacturers, the mount of the
lens itself isn't important because the
lens optics are designed for the
lens, and then the mount is simply adapted to suit.
So for the Milvus 21/2.8, you need to use the
lens profile for the Milvus 21/2.8, and not for any 21mm wide angle
lens(like the Distagon 21/2.8) .. the distortion if the Distagon will be different to that in the Milvus(maybe, dunno, never used either).
I've had a bit of a look into this in a bit more depth for 'ya too:
Seems like that you're using LR6.14.
Milvus 21/2.8 already noted.
Had a peek at the
lens profile page at Adobes website, and they say that for the Milvus 21/2.8, you need LR6.3 and or Camera
Raw 9.3. Ignoring the Camera
Raw component(LR is basically ACR with added ability!) and sticking with LR here, it seems that you need to update LR.
Possible reasons could be that the Milvus 21/2.8 is newer than LR6.14 and the
lens profile you've used could be for a different
lens.
Alternatively that if the Milvus 21/2.8 was an option in LR6.14 that you've used for the edit, maybe their original profile didn't correct for the specific distortion that the Milvus renders, and the update to LR6.3 fixes that.
Note that the camera used shouldn't make any difference here, other than it's sensor size.
Could be important only in that a crop sensor camera doesn't image the entire image circle of the
lens where the full frame camera does.
But the software used to correct the
lens profile correction pattern should take that into account automagically anyhow.