Untilting at Windmills (and other buildings)

Correcting the keystone effect

We’ve all been in the situation: there’s a building you really want to photograph but it’s on a street and the only way to get all of it in from so close is to use a wide angle lens and look up at it. The result? Keystone, which in this case is not the piece at the apex of an arch or vault, but the effect caused by photographing at an angle. Rather than being straight, the vertical lines of the building seem to take off toward some meeting place in the sky. Or the building leans, like this tower at the end of the Charles Bridge in Prague (above), which looks as if it is going to fall on the statue.

So what to do?

The easiest is to back off from the building if you can. The farther away you are, the less the angle, the less keystoning. Like Cary and I did with this church.

Or like I did in with the National Museum at the end of Wenceslas Square in Prague.

Even better at night:

The problem is that backing off can make you lose details. They get too small to be readable. Like in this photo of the PixBoomBa legal team (actually the judges of the High Court in Nairobi). If I’d gone far enough away to get the building straight, you’d hardly be able to see them.

If the building is on a narrow street and you can’t get very far away, see if you can get into a building across the street. Go up in the building until you are about half way up the one you want to photograph (try to equalize your distance between top and bottom). This can require asking people to let you into their apartment or workspace, but it can be done.

There are also special architectural lenses made just for this purpose. They are called tilt/shift lenses. But they are expensive and unless you do a lot of this sort of thing may not be worth it.

A lot of the time, we don’t mind keystoning (if it’s not too extreme). It feels like the way we normally see things, and does not detract from the image. Like in this photo of Cary’s:

Keystoning can reinforce the relationship between objects in the frame…

emphasize a part of the building you find particularly pleasing…

frame the image…

Or really make things soar.

There is one other thing you can do about the keystone effect: I could not get far enough away from St. Vitus’ Cathedral in Prague to get rid of the keystoning. I didn’t have a tilt/shift lens. (I didn’t have a tripod either. I make this image at 1.6 seconds, f5, 25mm focal length, by resting the camera on my camera bag.) But I wasn’t happy with the bent vertical lines, so I changed the perspective in Photoshop. (It’s done by transforming the perspective while using the crop tool. See PS help for details). If you use this technique, be sure to leave plenty of room around your subject—some of it gets lost during the transformation.

So think about your image. If the keystone effect does not bother you, if it does not interfere with what you want the image to say/mean, don’t worry about it. If you find it irksome, try to find some way to minimize it.

But remember that some buildings are meant to be slanted. You wouldn’t want to make the Leaning Tower of Pisa straight, for example, or this storm-damaged cottage on Cape Cod.

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