The first stop on our Antarctica trip next January, as it was back in 2002, will be Buenos Aires—a city that I loved and can’t wait to see it again.

In looking at my Buenos Aires photos from 15 years ago, one thing I noticed was that I hadn’t yet learned how to avoid “keystoning” when taking photos of buildings. Keystoning is what happens when you try to shoot a tall building and you have to tilt your camera up to get it all in. That tilt skews the building’s proportions and makes it seem as though the building is falling away. In this post I want to share with you what I’ve learned about how to avoid that problem.

At right is a shot I took of an iconic building in Buenos Aires’ colorful La Boca district. It’s an unusually shaped building to begin with, but notice how it seems to be leaning away from the viewer? That’s the keystoning effect, and it’s not ideal.

Over the years I’ve learned two different ways to prevent keystoning—one when you shoot the photo, and the other when you’re working with it in Photoshop.

I learned the first one from David Luria, an architectural photographer in D.C., on one of his Washington Photo Safari trips. When you take a photo of a building, you want the front of your camera to be perpendicular to the ground. Do that, and the building will appear straight. But that’s tough to do, especially with tall buildings, and especially if you’re standing directly in front of the building.

So the trick is to get as far away from the building as you can—or as far away as it takes in order for the front of the camera to be perpendicular to the ground. Because you’re farther away, the building in question might now be a lot smaller in the image, but that’s OK—you can crop in later in Photoshop.

To illustrate, Luria had us shoot an image of the Renwick Gallery in D.C. from the far end of its plaza. That allowed us to keep the building looking nice and upright, as you can see from the photo at right.

But all that dead space in the foreground isn’t contributing anything to the photo, so in Photoshop we just zoomed in on the part we wanted and cropped out the rest.

The result is the photo you see at left—which I realize is not exactly something the Pulitzer Committee would drool over, but at least the building isn’t tilting backwards.

Sometimes, though, getting farther away isn’t an option. In that case, you might be able to fix the keystoning in Photoshop.

I should stop here and admit up front that I do edit my photos. I use Photoshop to crop, straighten, color-correct, remove distracting objects, and more. If I were shooting photos for a newspaper, I wouldn’t be able to do that; it would undercut the journalistic integrity of the images. And if I were entering a photography competition where the rules said “absolutely no editing in Photoshop are allowed,” I’d of course abide by those rules. But I’m mostly taking photos for fun, to share with friends on Flickr and Facebook, and maybe once in a while to make a print to hang on my wall. So I don’t have any hesitation about using Photoshop to make them better.

Anyway, one way to make buildings stand up straighter in Photoshop—and I’m grateful to Julie Eggers for teaching me this—is via the Lens Correction option in the Filter menu. I’ll give you the step-by-step in a moment, but basically you move a slider to the left and watch as the building begins to become more upright. It’s quite cool. I’ll show you what it did to the above photo from La Boca in Buenos Aires shortly.

To be able to take advantage of this trick, though, you need a fair amount of sky above the building in the original shot; otherwise, as the building comes forward, it’ll soon start bumping up against the top of the frame. You can try to keep this in mind when shooting a building, and compose the photo a little loosely so you’ll have some sky to work with later in Photoshop. But if the picture you’ve got doesn’t have a lot of sky, no problem. You can create some in Photoshop.

Take a look again at that building in La Boca, at right. There’s a little sky above the building, but not enough for what I want to do.

So I went into Photoshop, chose the Crop tool, and drew a crop box that took in not only the entire image but another inch or so above it. Then I made sure that, at the top of the Crop screen, the box called “Content Aware” was checked.

(This “Content-Aware Crop” is new in more recent versions of Photoshop—and I have Alan Murphy to thank for pointing it out to me. He says it’s also available in the Snapseed smartphone app.)

I double-clicked inside the image, waited a few moments, and voila! Photoshop filled in the extra space I had created with pretty realistic-looking clouds and blue sky. Check it out at right.

That gave me enough headroom to use the aforementioned Lens Correction filter. Here’s how you do that:

1. Go up under the Filter menu and choose Lens Correction.

2. In the window that appears, click on the tab called Custom.

3. Toward the bottom of that window are some sliders, one of which is called “Vertical Perspective.” Move that slider to the left, and the building starts to stand up straight.

4. Click OK. You’re done!

I used this trick on the La Boca building, and the result is the image at right. The building still looks a little bit tilted, I realize, but I think it’s better than it was originally.

By the way, here’s an interesting article about the La Boca district from two women who travel together and who often have divergent perspectives on the places they visit. One found La Boca to be way too touristy; the other thought it was fun. Their photos are good—and their buildings are pretty straight.