Powerful Perspective Control - 6/15/09
Using tilt/shift the right way, the wrong way and the Photoshop way.
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Tilt/Shift (or perspective control) lenses are mechanically adjustable to provide special effects—like correcting for distortion and adjusting the plane of focus in the camera. Here’s how to make the most of the effects—even if you don’t have the lenses.The “right” way.
Architectural photographers most commonly use tilt/shift lenses to approximate the movements of a large format view camera in the digital format. These perspective controls ensure that parallel lines in a scene—say, those of an interior space or the exterior of a high-rise building—stay that way. The perspective controlling capabilities of these specialized lenses counteract the effects of keystoning that come from tilting the camera away from level; an effect that’s fairly common, and distracting, in architectural photographs. With the camera pointed up, tilt the lens down to make the building remain parallel. (The same principal works for horizontal corrections too, since the lenses are able to rotate and apply the movements to each axis.)
Another way to use a perspective control lens is to move the plane of focus—for example, to “lay it down” parallel with the plane of a tabletop in product photography. Slightly tilting the lens forward (down) will make subtle changes to the parallel lines in the scene as they relate to the camera angle, but dramatic changes to the plane of focus also occur.
The “wrong” way.
Both of the above approaches may be considered correct for utilizing a tilt/shift lens, but there are other equally valid ways to put them to good use—like throwing the plane of focus far out of whack, minimizing the depth of field dramatically and putting the center of attention in one very specific spot. This technique can be equally valuable, even if it’s not the textbook approach to working with a tilt/shift lens. The best part about working with this method is that it’s easy to achieve, experimentation is encouraged, and you can check your results right on the back of the camera. To put the plane of focus in a funky formation, first open up to a wide aperture—say, f/4 or better. Then tilt that lens. The farther you tilt, the more dramatic the shift. If you’re having a hard time making precise focusing, consider stopping down the aperture a bit, or make a less dramatic movement. And watch out for vignetting that can occur with an extreme tilt or shift.
The “digital” way.
Even if you don’t have access to such specialized lenses, you can recreate the effects of perspective control with a little bit of post production wizardry. To correct for converging lines in an image, open it in Photoshop and duplicate the background to a new layer. Using the Edit>Transform>Perspective control, grab the corners of the frame at the top of the image (if that’s where the lines appear to be converging). Dragging the corners away from the center will distort the image back toward the reality of parallel lines. You’ll notice that once the image is once again parallel (this can require some additional effort, like dragging the bottom corners of the frame in to the image to help achieve balance) it’s likely to look squished and unnatural. To elongate the frame again, increase the canvas size and again utilize the Transform tool, this time choosing Scale, to drag the top of the frame up to mimic the correct proportions again. There’s no hard and fast rule, so just eyeball it until it looks right. Lastly, you’ll need to crop the picture to eliminate the corners that are revealing the canvas underneath. Simply drag and double-click with the cropping tool until the image is exactly how it looked in reality.
The other “digital” way:
If you want to create the dramatic out of focus look of a super-shallow depth of field and a plane of focus that has gone whacky for good reason, you can do approximate the effect in the computer. Open Photoshop and duplicate your image onto a new layer. Using the marquee selection tool, create a vertical rectangular selection over the are of your subject that you would like to remain sharp. (Depending on the image, a horizontal selection may work well instead. The key is to make sure it’s only part of the available image.) With the lasso tool, add to the selection any crucial parts of the subject that you’d like to also be in focus. Likewise, subtract from the selection any areas that aren’t crucial to the area of focus. It’s this selection that will put the attention only where you want it to be. Next, inverse the selection and apply a minimal Gaussian blur to the area outside of the rectangle. This will be the first of three (or more) blurs that you will apply to an ever-widening selection area. Next, contract the selection to effectively expand the area that will remain unmodified, and blur it again. This time, get a bit heavier with the blur. Lastly, contract the selection again and really hit it hard with the blur. The idea is that the farther from the point of focus you get, the more blurry it will be. (If the blur has eliminated the “texture” of the original image file that comes from noise, utilize the Add Noise filter at a very low level to create the appropriate texture in the now blurred areas of the frame. Viewing an extreme enlargement of the transition between blurred and sharp parts of the image is the ideal way to make sure you don’t go overboard with the digital noise.) This is how it works with a tilt/shift lens thrown out of whack, so that’s what it should look like in the computer. The biggest difference? You can be particularly selective when you’re recreating the effect in the computer—meaning you can always be sure only the important parts of an image will be sharp, and everything else will go toward pointing your eye in the right direction. And if you work on a duplicated layer, a little layer masking is a great way to soften over-enthusiastic effects.
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