Correcting the Keystone Effect in Photography

If you love architectural photography as much as I do, surely you have dealt with the Keystone Effect. The Keystone Effect, also known as perspective distortion is caused when shooting a subject at an extreme angle resulting in converging vertical(also horizontal) lines which especially in architectural photography is not desired. The same thing also happens when projecting an image at an extreme angle as many of us older people remember from the days when teachers used overhead projectors in school.

Here is an example of the keystone effect.
Keystone effect

Preventing distortion in the first place
The best way to deal with perspective distortion is to change your perspective! Duh. The further you move back from the subject, the less extreme angle becomes resulting in straighter lines. This is why the keystone effect is more pronounced when using ultra wide angle lenses. In the example above, I was using my 14-24 mm lens and was relatively close to the very large building which was a recipe for extreme distortion.

In this example, I was using an 85mm 1.8D lens (last weekend before I upgrade it but that’s a different story) to shoot a much taller building yet, The Keystone Effect, while not eliminated completely, is much more natural and pleasing. In fact, I made absolutely no effort in correcting it because it seems more like what the eyes see.

Hard Rock Cafe guitar

In the above example, I had the luxury of walking across the street and having the Bank of America building be a few blocks away, but what if you don’t have that luxury? The next best thing would be to find a way to take the picture from the middle. Perhaps, there is a hill or another building across the building that you want to photograph.Maybe you have access to a ladder. Anything you can do to lower the angle that you shoot at will help.

Also, don’t forget that you don’t always have to get the entire building in order to have a good picture. Here, is a very simple picture that shows off the architecture in the background. There is almost no distortion here because I am standing far.
Wortham Theater

Tools to help with perspective distortion

Sometimes (actually many times) there is just no getting around it. You can’t backup anymore because there is either a ditch, traffic, a tree, or another building behind you. So what can you do? How’s a brother going to take a picture of a tall-ass building without perspective distortion? The method of choice would be to get a tilt shift lens and correct the vertical distortion while shooting.

As is the case with most photography equipment, tilt shift lenses are expensive! in a perfect world, we would have access to every kind of specialty lens available, but the reality is that we all have to make certain sacrifices when choosing our equipment. For me, I tend to use my ultra-wide-angle lens far more than I would a tilt shift lens. Using a tilt shift also requires a certain skill level and patience. I don’t have either.

Fortunately, Photoshop and Lightroom provide you with very powerful lens correction tools when you shoot your pictures in raw. You have to keep in mind however that depending on the level of distortion, you will end up cropping part of your picture when you tilt the picture virtually. Because of that, you should be aware of the time of shooting and use a wider focal length while you are shooting. It also helps greatly to minimize horizontal distortion because correcting the two at the same time is much more complicated and because you’re dealing with math, every adjustment you make will result in a little bit of segregation of your picture. In my example above, I didn’t take the best technically sound picture as I am not exactly center of the building, but I did use a wide enough angle (I think I used 15mm on full frame) so there is some wiggle room.

After playing with the vertical adjustment in the distortion tools in light room, this was the following result:

Wortham Theater (After Keystone Effect Correction)

Of course, I am not claiming that this is perfect by any stretch of the imagination; however, it is much better than the original.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s