Fixing wide angle distortion

[whited3]

I've recently started using a canon EF-S 10-22mm f3.5 which replaced my Sigma 10-20 f3.5 which was stolen. I seem to get a lot more distortion at 10mm using the Canon compared to the Sigma. First image taken this morning has had auto lens correction applied in ACR.

In the second image I've used Warp in CS5 (after auto correction in ACR) to try to correct some of the distortion by working on the lamp post in the foreground.

I need to do some more detailed work to straighten the lamp post but to my eye the foreground floor timber is now slewing off to the right.

Comments, suggestions please

[Photon Hacker]

Hello.

I'm not able to see distortion in either image. Have you measured it or do you suppose it is present?. Bear in mind than in the common rectilinear perspective not all actual vertical lines (Such as the lamp pole, it seems) will image as vertical lines if you're shooting with the camera tilted below horizon (As it's the case here) or above it; this is noticeable with wide angle lens. Don't confuse distortion with perspective.

I don't know for existing tools for distortion correction, let alone for Photoshop which is proprietary software and hence I don't use it.

I'd suggest to measure distortion by shooting an uniformly spaced concentric ring pattern with the lens pointing perpendicularly to the center, then you can accurately describe the transform function by measuring the apparent distance of the circles, invert it and apply it to the images taken with that lens. Note It's also possible for a lens to show distinct distortion at distinct focal distances.

However, if you decide to "correct" the distortion in an image editor by sliding bars be sure to actually correct distortion (Straighten straight lines) and not perspective. It might not be as accurate as a systematic method but it seems to be good enough for many photographers.

Regards.

[FrankMi]

Hi Mark, I would also experiment with Skew, Perspective, Distort, and even Puppet Warp. Once you get familiar with them you'll get a better feel for which one to use for each aspect of the image you are trying to correct.

I find sliding the horizontal and vertical guide lines can really help determine what to change and by how much. The straighten feature of the ruler tool can also give you a great starting point, particularly for leveling horizons.

You can minimize wide angle distortion by keeping the camera as level in roll and pitch as possible when shooting.

[whited3]

Thanks guys. You got me thinking so I went back to CS5 lens correction and did a custom correction on verticals only. I found that concentrating on getting the foreground lamp post vertical skewed the image too far so instead, I zoomed in and worked with the verticals on the pergola further down the pier.

I also did a 1:1.8 crop which I think works better with the perspective.

[accystan]

Hi Mark:

I use two procedures in P/S to get pics to my liking. For the first one I put a grid up on the screen (alt>vhg). Then, Select>All, then, Edit, Transform>distort. I manually drag the corners to get the horizontals and verticals to my liking. The second procedure I use is Filter> distort> lens correction.

I also use the 'measure' tool (then rotate> arbitrary> return) to make sure my horizons are horizontal. For the most part we almost always like to see level horizons

I find it interesting, and it's largely a matter of taste, but for some reason objects receding in size in the horizontal plane (i.e. 'normal' perspective) seems to be completely acceptable to us whereas vertical perspective changes seems less so (i.e. tall buildings getting narrower and leaning backwards etc.).

Good pic. by the way.

Dave D