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14-24, 2.8. Volume anamorphosis correction


roypanos

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<p>I have the 14-24 2.8 Nikon wa zoom, and it's an amazing lens. But, and it's a big but, (no pun intended, just a by-product) I find the distortion at the wide end disturbing. Some time ago I tried the evaluation version of DxO for a couple of weeks - and just missed out on the discounted offer - which has the brilliant facility of automatically mapping out the distortions for Nikon's principal lenses (why doesn't NX2 do this?) and includes the ability to compensate for the anamorphic distortion.</p>

<p>I've got used to using NX2 and I'm really happy with the results it produces, despite the bugs and the clunky interface, so I don't actually feel inclined to spend money on another RAW converter. Is there another cost-effective (aka cheap) way of achieving this form of correction? I have PTGui for example, however other than defishing a 10.5 FE I've not used it for any distortion corrections.</p>

<p>How do other users deal with this "problem" in a widely praised lens? I did a group shot at a party recently and the people at the outer edge of the group would be justified in insisting that this limitation of the lens certainly leads to, ahem, a big but...</p>

<p>Roy</p>

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<p>Well, yes it's undoubtedly the <em>wrong lens </em> for a group photo! But I used it as it was the only way of getting everyone in in such a confined space. But the phenomenon is noticeable in many contexts.<br>

I was getting a sample organised before these responses. This is an uncropped jpeg out-take which has subjects at the extremities. I actually thought that this phenomenon was so well known as to not require illustration.</p><div>00UG0u-166411884.jpg.3cf1f89decd09f57b7c2357885b5e885.jpg</div>

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<p>The 14-24 has some barrel distortion at the widest setting which is something the lens designers try to minimize (a flaw).</p>

<p>What you see however is an effect of perspective and rectilinear rendering. Only DxO and I think a photoshop plug in or two can handle this. That's why wide angles aren't used much for people photography.</p>

<p>You can kind of fix it in photoshop though without extra software. Select the outer edges of the image and sqeeze it together. Then crop the image if you like to keep the aspect ratio.</p>

<p> </p>

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<p>Your image does not show that much geometrical distortion, look at the vertical lines they are very good. Nikon Capture NX 2.2 does have distortion correction, it is under c<strong>amera and lens correction </strong>it is OFF by default, you need to set it to auto.</p>

<p> </p>

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<p>In the picture the man on the left has head 3 times larger than a manin the central portion. What else would you expect ? He is much closer to the camera. You would not find a wide lens that would behave differently. This is normal undistorted beavion of a very wide lens.<br>

It was already explained as geometrical perspective.</p>

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<p>I don't think the people on the edges are all that much closer to the camera compared to those in the center of the frame; in fact, they should be farther away. The real problem is that you are projecting something that is 3D onto a flat, 2D sensor and then view it on a flat monitor.</p>

<p>Based on the link Roy provides, I am not all that impressed with what DxO can fix. In particular, they chose sample images without much of a background to deal with. It'll be interesting to see how Roy's house gets distorted if you put this image thru their fix.</p>

<p>As usual, you are always much better off getting it right when you capture the image.</p>

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<p>Pete says:<br>

<em>"Only DxO and I think a photoshop plug in or two can handle this. That's why wide angles aren't used much for people photography."</em><br>

Any idea which plugins, Pete?<br>

The effect is apparent in other contexts too - a stretching at the periphery. It's not particularly acceptable (even if less obvious) with other subjects. It seems that what is being generally asserted in the responses here is "<em>Problem? What problem?</em> " But obviously DxO have identified it as worth adressing, not just this challenged old fella. If you can reduce the effect, why wouldn't you? The examples they offer on their website are pretty good - they exhibit just the same kind of "distortion" that I've seen lots of times and wished gone, although I don't photograph pool tables very often. The reason I started the thread is that I noticed it yet again in some other shots I took today. It's particularly noticeable when the periphery of the shot is foreground, especially when the shot's in portrait format.</p>

<p>Aresh says:<br>

<em>"Your image does not show that much geometrical distortion, look at the vertical lines they are very good. Nikon Capture NX 2.2 does have distortion correction, it is under c<strong>amera and lens correction </strong> it is OFF by default, you need to set it to auto."</em><br>

Yes, of course, I know this: my fault if I seem that stupid. But what I'm trying to describe is stated clearly in the title of the thread,</p>

<h2>14-24, 2.8. Volume anamorphosis correction</h2>

<p>and I'm using DxO's own terminology for this effect, not mine - which is I assume is precise. It seems to be the word "distortion" that's causing some respondents to balk. I'm really not that smart but I understand the basic difference between the "volume anamorphosis" effect and geometric lens distortion etc. So semantics aside, whether it's "distortion" per se or not, I'll repeat the question. Apart from DxO, how to correct it? It's ugly whether it impinges on a bush or a human torso. I'm not sure how you could do it in PS as it's obviously non-linear and DxO's own solution is variable depending on subject.<br>

Or does no one bother about it? Or only DxO users?</p>

<p>Roy</p>

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<p>Missed a couple of responses whilst typing the above.<br>

With regard to "get it right in the first place". Yes, always the best solution, no doubt. But how to shoot a group like this without bulldozing a garden wall away? Stitching? No thanks.<br>

It may well be that DxO's examples would look worse if the backgrounds were different but in the case of the shot I posted (or at least the final version used) it would be a lot better if the "distortion" was manifest in the building rather than the breadth of the people at the extremities.<br>

I'd like the option to correct it. But....</p>

<p>Roy</p>

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<p>Roy, if you have a group of people that are willing to cooperate with the photographer, I would line them up at least with a front and a back row or perhaps 3 rows. In the FX format, any time you need to shoot a group with anything wider then 35mm can be problematic. If I have no choice, I may use something like 28mm. Anything wider will likely become a disaster.</p>

<p>Of course, if you have non-cooperating subjects, that is a different story.</p>

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<p>A good wide angle makes a perfect "rectilinear projection" and that is what you see. Straight lines remain straight, and objects near the edges get sucked out to the edges.</p>

<p>The normal way to deal with this using a program such as PTGui (which you have), Hugin (which is free) or PTAssembler, is to select a different projection (aka "mapping") mode. You will find that a cylindrical projection will make the people look pretty good, but the building will be warped in an interesting way. Other projections you might try are a Lambert cylinder equal area, Mercator, or Miller.</p>

<p>If you arrange your people so that they really form a section of a cylinder, a semicircle at equal distance from teh lens, then the cylindrical projection produces totally distortion free people. I typically do that, and try to choose a natural background that won't look mutiilated by the mapping.</p>

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<p>Roy, nobody said you seem stupid, but the title implies there is a particular and unusual distortion associated with 14-24, this type of distortion has nothing to do with the particular lens in question it is the result of projecting a volume into a surface so it has nothing to do with <em>"mapping out the distortions for Nikon's principal lense" </em>you were asking above. You also mentioned <em>"problem in a widely praised lens" ,</em>this leads people to believe you are looking for a sw that can correct geometrical distortion with a particular table for Nikon 14-24 f/2.8<br /> <br /> If you want to correct perspective you can use PhotoShop's free transform feature, or you can use cylindrical projection in PTGui, you can also dial in correct transform parameters to project your flat image into a curved surface using PTGui to correct this, but then the building and other stuff will look "distorted". Overall I think PTGui is the best sw for this type of correction, it may not be the easiest to use though.</p><div>00UGB9-166457784.jpg.3102439f7d7d0d451f7b100e0fb0daa1.jpg</div>
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<p>As I said before you can kind of fix it in photoshop. Select say 25% of the left side of the image and do free transform and squeeze the side together until the people standing 25% from the edge looks right. Then repeat but select the outer 15% and squeeze it togehter a little bit more and then another time with just the last 10%. Repeat on the other side.</p>

<p>I did that then selected the lens correction to fix a little rotation, a little barrel distortion and a slight perspective correction. I left the edges so it's easier to see. Final step would be to crop the image.</p>

<p> </p><div>00UGCX-166465584.jpg.2d83b25dd061480999365a305a1adc8b.jpg</div>

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<p>Wow this an educational thread. I didn't know my 14-24 had any appreciable distortion but then I never shot any large group type shots with it either. The lens has always worked really well for me for everything I've ever used it for, mainly landscape type shots. As long as I keep the camera totally level on the tripod it will shoot nice architectural / interior as well with almost no distortion. I really didn't think the original shot looked bad but then I am still learning a lot about all this stuff.</p>
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<p>OK, I came up with a better and less work intensive correction in photoshop (CS2 in this case).<br>

1. do filter > distort > spherize, set to 25% and horizontal only.<br>

2. do select > all<br>

3. do edit > free transform, set W (width) to 91% and apply changes.</p>

<div>00UGDk-166469584.jpg.b48bec8032775507332579594baeb36c.jpg</div>

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<p>I have the 14-24/2.8. I don't often use it for portrait type work, but I was fooling around the other day at the dump with my father-in-law. The first photo below was made with a D700 with the 14-24/2.8 at 14mm, 1/400s, f/10, ISO 200, matrix metered. The image is an unaltered camera jpg. The second image is the same photo run through the DXO volume anamorphosis correction. I don't remember the exact settings for the correction engine. </p><div>00UGDw-166469784.jpg.08c8f52f948833e11a0aec96bda512ca.jpg</div>
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<p>Here's a jpg of Doug's Man with Broom image that I fixed in the photoshop program. The difference between the fix that he posted and the fix that I posted is: In mine, the head is more evenly proportional with the body.</p><div>00UGG8-166479584.jpg.a3ec61d8c3c3ccb313d207fc652a160c.jpg</div>
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