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April 19, 2011 - Architectural Photography - Part 1

I recently got to do some photographs of the Boone County Courthouse for a client, and this job exposed a lot of what makes architectural photography both difficult and fun. By and large, it all boils down to the difficulty of shooting something really big from a postion way too close, and (often) way too low. Let's face it, buildings are big! And if you try to get far enough away to shoot them without wide-angle distortions, there's always irksome trees, other buildings, telephone poles, roads, etc. in the way. And buildings are tall, too, so you're not shooting horizontally, but instead looking up at them, and that creates other (trapezoidal perspective) distortions and focus issues. Because of these problems, you typically end up with images like the one at the right.

This shot shows all the problems. In order to get the flag from the Armory across the street reflected in the window, and hide the Armory's chimney behind one of the vertical columns separating the windows, I had to shoot from that particular spot. I had my trusty 24-105 mm lens set for full wide angle to get as much of the building as possible in the shot, but that caused the vignetting at the corners and the barrel distortion (apparent bulging at the center). Furthermore there were power lines in the shot (though fortunately not in front of the building - I could control my position that much, at least!). Because I was shooting at an angle to the building (i.e., the plane of the camera's back and the face of the building weren't parallel), there are perspective distortions too. I was closer to the left side than the right so it's smaller on the right, and I was at street level, closer to the bottom than the top, so it's smaller on top. There's not a vertical or horizontal line anywhere in that image! Also because of the non-parallel planes, I had to shoot with a small aperature (high f/ number) and a correspondingly long exposure and higher ISO to keep the entire building in sharp focus. I did use a circular polarizing filter on the lens to control the glare, but unusually in this case I rotated it for maximum reflection in the windows to bring out the flag.

It helps to have a client (as I did in this case) who is sophisticated enough to know that these issues are typical and can be corrected. Otherwise you have to either edit all of your images before making proofs, or give detailed explanations about issues that the client can ignore in the proofs with the assurance that they'll be fixed in the edited images. Even with an experienced client like this one, you have to worry that they can't see what the image will be, over what the proof shows it to be at first. There is also the reality that post-production to take care of these problems is time-comsuming, and you will have to bill accordingly. For example, I spent about 15-20 minutes editing this shot, and some images can take even longer!

Many, but not all, of the problems in this shot could have been avoided with appropriate camera technology. Ideally, one would use a view camera (one of those old-fashioned looking cameras with a bellows separating the lens from the camera back). This would allow the lens plane and film/sensor planes to be moved independently which would correct for the perspective distortions and focal plane issues. Unfortunately, I don't have a view camera. One could also use a tilt-shift lens which would provide many of the same features. Unfortunately such a lens costs about $2,400, so I don't have one of those either (though if someone wanted to buy me one, I'd be eternally grateful!). Since I didn't have either of these means available, I had to make do with post-production technology, namely, Adobe™ PhotoShop.

The order in which you fix these problems in PhotoShop is extremely important. In the raw converter, I take care of color temperature, exposure, black-level, and clarity, leaving things a little dark so I don't have any blown highlights. The rest I leave for PhotoShop proper. Once there, I first adjust the image rotation (in this case I had to rotate it about 1½° clockwise), and then open the lens correction filter (under the Distort menu). Using this I was able to correct the barrel distortion, and adjust both the horizontal and vertical perspectives. The grid provided in this filter is really helpful at making your adjustments. I purposefully did not fully correct the image's distortions, especially in the horizontal, as the image was clearly taken from an angle (as evidenced by the sides of the protruding bits showing). Too much correction would look very wrong, but a certain amount is very helpful. In general, with architectural images, it is perfectly ok to have horizontal lines converge for perspective, but your verrtical lines should all be pretty darn close unless there is an obvious and deliberate vertical perspective.

Next I cropped the image to remove the worst of the vignetting as well as the blank areas from the perspective correction. I then cloned out the power lines, created a Curves adjustment layer to balance the light and shadow, added a separate Curves layer with a gradient in its mask to darken the right side of the image (where it is in bright sun) relative to the left and center. This also helps draw the eye to the center section of the building which I wanted to emphasize. I was careful when adjusting the curves to keep the lovely texture in the rough stone above the big windows that was so accentuated by the low-angle light of the setting sun. The end result is shown at the left. I think you'll agree it's a significant improvement!

Next week I'll look at some more shots from this shoot, showing how you can combine several images to form panoramas that couldn't be captured in a single shot. Happy shooting!
-Art

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