distortion

[jamesmartin]

the pics from my last few trips ive noticed distortion on my horizons that haven't occurred before so was wondering if anyone can help please. the lens is my zeiss milvus 21mm that ive been using for the last few years & like I said have never had this issue until recently


this one I haven't clicked on Enable Profile correction. the middle part of the horizon is bulging a bit higher then the sides
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this one I have clicked the Enable Profile Correction. its fixed the middle & left side but the right edge of the horizon is now higher then the rest
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my camera is Canon 5DsR

[ameerat42]

James. Lots of wide-angle lenses show a bit of barrel distortion (https://en.wikipedia.org/wiki/Distortion_(optics)).
You're doing all the right things. You'd have to decide how practical it would be
to move straight lines of subjects away from the edges of the frame in your
compositions. Else, just keep applying that fix.

[jamesmartin]

James. Lots of wide-angle lenses show a bit of barrel distortion (https://en.wikipedia.org/wiki/Distortion_(optics)).
You're doing all the right things. You'd have to decide how practical it would be
to move straight lines of subjects away from the edges of the frame in your
compositions. Else, just keep applying that fix.

thanks mate. ive only just noticed recently that it doesn't fix some pics completely so thought something must of been wrong with my lens. cheers

[Tannin]

As AM says, all lenses have some distortion, wide-angle lenses in particular. The lens designer can add corrective elements to reduce it - reduce it to almost nothing if desired - but these corrective elements introduce their own problems, such as reduced contrast, other types of distortion (including some much more difficult to correct in post), and chromatic aberration. (Not to mention cost, bulk, weight and complexity.) My guess is that Zeiss deliberately decided to go for ultimate sharpness at the cost of a little distortion. That would (I suspect) fit their design philosophy.

Other makers make different design compromises. I bet you that (for example) my Canon 16-35/4L will have less distortion (almost sure of that) but I'll also bet that your Zeiss is sharper. Design trade-off.

Your best bet (albeit at considerable cost) might be an architectural lens, such as the Canon TS-E models. These are designed to provide near-zero distortion and are said to be very, very sharp. Is it worth it for you? Probably not. If you'd like to try one out though, I have a 24mm TS-E I don't use often which you would be very welcome to try out.

[John King]

James, leaving aside various lens distortions that occur with UWA lenses, always remember that the horizon is actually curved. Just not quite like this ... ;).

[jamesmartin]

As AM says, all lenses have some distortion, wide-angle lenses in particular. The lens designer can add corrective elements to reduce it - reduce it to almost nothing if desired - but these corrective elements introduce their own problems, such as reduced contrast, other types of distortion (including some much more difficult to correct in post), and chromatic aberration. (Not to mention cost, bulk, weight and complexity.) My guess is that Zeiss deliberately decided to go for ultimate sharpness at the cost of a little distortion. That would (I suspect) fit their design philosophy.

Other makers make different design compromises. I bet you that (for example) my Canon 16-35/4L will have less distortion (almost sure of that) but I'll also bet that your Zeiss is sharper. Design trade-off.

Your best bet (albeit at considerable cost) might be an architectural lens, such as the Canon TS-E models. These are designed to provide near-zero distortion and are said to be very, very sharp. Is it worth it for you? Probably not. If you'd like to try one out though, I have a 24mm TS-E I don't use often which you would be very welcome to try out.

Thanks tannin, interesting stuff!
I guess I can't complain then as I like as sharp as I can get.
I think for now I'll just stick with the zeiss & work on my skill of taking pics & PP.
Thanks for the offer

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James, leaving aside various lens distortions that occur with UWA lenses, always remember that the horizon is actually curved. Just not quite like this ... ;).

Thanks john

[tandeejay]

Looking at the second image, it looks like the barrel distortion correction that has been applied is just a little bit too much. 1st image the horizon is curved down, 2nd image the horizon is curved up... Can you adjust the strength of the correction? ACDsee has a manual correction slider in the Lens Correction section which allows you to tweak how much distortion correction is applied. I'm fairly sure LR has something similar, but don't have it anymore to be able to check...

[jamesmartin]

Looking at the second image, it looks like the barrel distortion correction that has been applied is just a little bit too much. 1st image the horizon is curved down, 2nd image the horizon is curved up... Can you adjust the strength of the correction? ACDsee has a manual correction slider in the Lens Correction section which allows you to tweak how much distortion correction is applied. I'm fairly sure LR has something similar, but don't have it anymore to be able to check...

Thanks John, yes it did help a bit

[arthurking83]

John got it in one hit.
Second image looks worse as the distortion is much less natural looking. To me, the edited image looked less 'attractive', as you never see concave distortion on the horizon.
So a teeny tiny amount of distortion, barrel or convex type isn't such a bad thing .. unless it's madly obvious.
Cheap .. as in the really cheap consumer kit type lenses, that go from 18-<whatever> give you this madly obnoxious barrel type distortion .. and the bigger the <whatever number>, the more crazy the effect too.

Like Tony(Tannin) said too, each lens is designed in a specific manner by the engineers, and distortion, front element size all have a say in how distortion is rendered.
What I mean by that, is, even tho a wide angle lens may be say f/2.8, it's front lens may be far larger than the aperture specs allude too.

eg. a 200mm lens with an f/2.8 aperture(which is the front lens remember) really only needs a 72mm front lens element, and with that almost all 70-200mm f/2.8's have a 77mm front lens. They make it a little larger to make the overall design easier to create .. but 77 -> 72mm is only 5mm, so just gives you an idea of how lens design works.
That is, if a lens is 200mm and f/2.8 and the front lens is only 67mm or 52mm .. you know that the lens maker of a lens like that is pulling your leg .. ie. it just won't happen!

So, a wide angle lens uses some fairly extreme design in it's optical path, and theoretically, a 21mm f/2.8 lens, really only 'needs' a 7.5mm front lens element!
But the optic design, the bending of all that light is extreme, so we never see a wide angle lens with a small front lens element, they're usually very large(considering the specs).
This is where the distrotion basically comes from .. the design of the front lens element. Bigger is usually better to a certain degree. more specifically, overly bigger than the specs would normally describe .. is better.

One thing to note too, when you tilt the lens upward or downwards will almost always accentuate the distortion more too. Again this is all down to lens design too.
So keep the camera level and horizon centred will more likely create less distortion along the horizontal.

[ameerat42]

So, a wide angle lens...
One thing to note too, when you tilt the lens upward or downwards will almost always accentuate the distortion more too. Again this is all down to lens design too.
So keep the camera level and horizon centred will more likely create less distortion along the horizontal.

Keeping to wide-angle lenses...
Doing what AK says will also keep the lean of straight lines (verticals or horizontals) minimised.

The reason leaning lines appear accentuated in w-a lenses is that you can easily tilt such lenses compared to
longer ones AND the field is so wide that you easily capture the effect.

Another distortion (correct term) in very wide lenses that project a rectilinear image is the s-t-r-e-t-c-h-i-n-g of
subjects away from the centre of the field. It is particularly noticeable in a Σ8-16mm that I have. - Oh, well :confused013
it's good for landscapes, where you don't notice it.

[arthurking83]

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.

[jamesmartin]

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.

thanks for the detailed explanations arthur!! ill have to re read it a few times lol but interesting stuff. my lightroom/PS/CR are always updating so ill see what version i have atm. yes my concern was that it was moustache. anyway its good to learn about all this