Correcting Lens Curvature? - DPChallenge Forums

03/23/2009 03:50:13 PM · #1

hey guys,
how do you go about correcting lens curvature? how do you ensure its really straight?
for example, on a shot i took over the weekend (below), i used a combination of perspective, distort, and warp, to try and get the building looking grid-like straight, but it's still a bit off.
any tips?

03/23/2009 04:05:09 PM · #2

In CS3, filters>distort>lens correction: find the sliders for barrel distortion and get rid of the curvature first. The preview is large,a nd there's a grid on it, so that can be done precisely.

THEN (and only then) use edit>transform> perspective and/or skew to clean up the verticals and horizontals.

The barrel distortion is always symmetrical, so you need to correct for that first, because once you start skewing it gets asymmetrical and then you *can't* correct for it. All this wants to be done on the uncropped image, btw, for the same reason.

R.

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

03/23/2009 04:05:47 PM · #3

Originally posted by Bear_Music:

ah, awesome. will give that a go tonight. cheers!

GeneralE

Canon PowerShot S3 IS

03/23/2009 04:11:03 PM · #4

Originally posted by Bear_Music:

In CS3 ...

And I thought you were going to suggest that using a tilt-shift lens (see recent threads) would avoid the problem in the first place. ;-)

03/23/2009 04:11:37 PM · #5

Originally posted by GeneralE:

Originally posted by Bear_Music:
In CS3 ...

And I thought you were going to suggest that using a tilt-shift lens (see recent threads) would avoid the problem in the first place. ;-)

throwing hardware at problems is my favourite solution.

03/23/2009 04:16:31 PM · #6

Originally posted by k4ffy:

Originally posted by Bear_Music:
In CS3, filters>distort>lens correction: find the sliders for barrel distortion and get rid of the curvature first. The preview is large,a nd there's a grid on it, so that can be done precisely.

THEN (and only then) use edit>transform> perspective and/or skew to clean up the verticals and horizontals.

The barrel distortion is always symmetrical, so you need to correct for that first, because once you start skewing it gets asymmetrical and then you *can't* correct for it. All this wants to be done on the uncropped image, btw, for the same reason.

R.

ah, awesome. will give that a go tonight. cheers!

Actually, I just remembered that the lens correction interface has a couple of perspective sliders also, so you can use those for gross adjustments. But they'll only work perfectly if the keystoning is symmetrical, so you may have to use the skew tool also.

R.

mpeters

Canon EF 50mm f/1.8 II

03/23/2009 04:26:08 PM · #7

Do you know how well, or if this tool works for 'volume anamorphosis distortion'?

link to DxO site with explanation using their software to correct this issue. link

03/23/2009 04:37:50 PM · #8

Originally posted by mpeters:

Do you know how well, or if this tool works for 'volume anamorphosis distortion'?

link to DxO site with explanation using their software to correct this issue. link

DxO is *really* good at correcting for this problem, no kidding. From all I've read, state-of-the-art. I guarantee ya if I was still doing architectural photography for a living I'd be all over it. But I'm fortunate that my 10-22mm is world-class in its freedom from barrel/pincushion distortion and since I got the 20D I haven't had to use this sort of correction at all. It's not a problem with *any* of my current lenses, actually.

When I was shooting with the Fuji, and then the Nikon, P&S cameras it was a real issue, and that was before I had CS3 of course. There was another 3rd-party guy, Richard Rosenmann, that had a nifty filter for fixing this that worked in PS7, and that's what I used.

R.

mpeters

Canon EF 50mm f/1.8 II

03/23/2009 04:47:32 PM · #9

Originally posted by Bear_Music:

Originally posted by mpeters:
Do you know how well, or if this tool works for 'volume anamorphosis distortion'?

link to DxO site with explanation using their software to correct this issue. link

DxO is *really* good at correcting for this problem, no kidding. From all I've read, state-of-the-art. I guarantee ya if I was still doing architectural photography for a living I'd be all over it. But I'm fortunate that my 10-22mm is world-class in its freedom from barrel/pincushion distortion and since I got the 20D I haven't had to use this sort of correction at all. It's not a problem with *any* of my current lenses, actually.

When I was shooting with the Fuji, and then the Nikon, P&S cameras it was a real issue, and that was before I had CS3 of course. There was another 3rd-party guy, Richard Rosenmann, that had a nifty filter for fixing this that worked in PS7, and that's what I used.

R.

I asked because I shot a rather large family group with my 17-40 and even though I left plenty of real estate around the edges, there was still some distortion visible on the heads near the edge. I had to shoot at about 20-23mm to keep my lens element in the shade of a chimney. I hate to purchase the program for one print--and a gratis print at that!

I don't think the 17-40 shows much barrel distortion, even at the widest of angles, but this problem was pretty apparent.

03/23/2009 05:33:32 PM · #10

Originally posted by mpeters:

You sure you're not just talking about plain, ordinary wide-angle distortion of objects near the edge of an ultrawide image? Is that what "volume anamorphosis distortion" is? Making spheres look oblate? That's entirely a function of how wide is the angle of view and how close to the edge you are, and it's NOT an optical distortion introduced by the lens. Now, I don't know if there's any sophisticated software that is designed to compensate for that, but it's just part of being WA to me.

What we're discussing here is the tendency for straight lines to bow near the edges...

R.

Mick

Canon EF 70-200mm f/2.8L IS USM

03/23/2009 05:37:08 PM · #11

Originally posted by mpeters:

I don't think the 17-40 shows much barrel distortion, even at the widest of angles...

My Canon 17-40mm lens shows some barrel distortion at the wide end. I use PTLens to correct. The built-in camera/lens profiles make it easy to use, and it does a great job.

mpeters

Canon RF 24-70mm f/2.8 L IS

Canon EF 50mm f/1.8 II

03/23/2009 05:41:52 PM · #12

Originally posted by Bear_Music:

Originally posted by mpeters:
I asked because I shot a rather large family group with my 17-40 and even though I left plenty of real estate around the edges, there was still some distortion visible on the heads near the edge. I had to shoot at about 20-23mm to keep my lens element in the shade of a chimney. I hate to purchase the program for one print--and a gratis print at that!

I don't think the 17-40 shows much barrel distortion, even at the widest of angles, but this problem was pretty apparent.

You sure you're not just talking about plain, ordinary wide-angle distortion of objects near the edge of an ultrawide image? Is that what "volume anamorphosis distortion" is? Making spheres look oblate? That's entirely a function of how wide is the angle of view and how close to the edge you are, and it's NOT an optical distortion introduced by the lens. Now, I don't know if there's any sophisticated software that is designed to compensate for that, but it's just part of being WA to me.

What we're discussing here is the tendency for straight lines to bow near the edges...

R.

Ya, I think it is two different things. I understand the barrel distortion but i'm hoping I can correct for the other "problem" without purchasing the DxO software. This WA distortion plays havoc with a person's mostly spherical head! ;) DxO claims to have the solution and I was hoping that someone might have tackled this problem with PS.

thanks for the link Mick. Most of the time, I don't mind the 17-40 distortion. An occasional sea horizon gets bent, but that's about it. And it seems minimal to me...

kirbic

Canon EOS R5

03/23/2009 08:55:50 PM · #13

Originally posted by mpeters:

...This WA distortion plays havoc with a person's mostly spherical head! ;) DxO claims to have the solution and I was hoping that someone might have tackled this problem with PS....

The oblateness of round (or spherical) objects near the edge of a WA field is not a distortion, but a fact of life with WA rectilinear lenses. For the rectilinear "mapping", straight lines remain straight, but circles get stretched near the edges (actually they are only perfect when perfectly centered). For an equiangular fisheye, by contrast, straight lines are curved (unless perfectly centered) and round or spherical objects are always round. Fun fact.

03/23/2009 09:08:43 PM · #14

so, i think i need a bit more advice on this...
here's my original:

if i correct vertical/horizontal perspective before getting to the lens correction bit, i lose a large percentage of the image's pixels.

how would you approach this? let me know if you'd like original size (21.1MP)

thanks!

03/23/2009 09:23:29 PM · #15

Originally posted by k4ffy:

so, i think i need a bit more advice on this...
here's my original:

if i correct vertical/horizontal perspective before getting to the lens correction bit, i lose a large percentage of the image's pixels.

how would you approach this? let me know if you'd like original size (21.1MP)

thanks!

E$dit>transform>perspective, then edit>transform>skew, then edit>transform>warp, then for the hell of it Topaz Adjust "spicify". This doesn't work well with the distort/lens correction filter. It ain't perfect, but I have never had to deal with this extreme a case before.

03/23/2009 09:25:44 PM · #16

hmm actually worked really well. so i guess the lens correction is for shots that are more or less straight on, and don't need as much perspective correction. the normal perspective/distort/skew tools are better for a case like this?

cheers.