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Monday, June 30, 2014

Get Higher Resolution With a Tilt-Shift Lens

Make your lens wider and the resolution greater with this tilt-shift technique

This Article Features Photo Zoom


Digital Photo Tip Of The Week
Most photographers who employ a tilt-shift or perspective control lens do so for one of two reasons: to combat distortion in architectural images or to change the plane of focus. But there's a third use for a tilt-shift lens that's particularly powerful: It can create a wider angle of view and a higher resolution image file just through one simple movement.

The concept is simple: Because the tilt-shift lens can shift side to side and up and down, it can very easily be used to create a trio of exposures that seamlessly fit together in a composite. Because you haven't moved the sensor at all, only the lens' position laterally in relation to it, there's no rotation of the lens or movement of the sensor that makes seamlessly blending a challenge. You might try three horizontal images that shift left and right to form a panorama or rise and fall to create an image that maximizes the view in a vertical orientation. Either way, the approach is the same.

To start, ensure that you're using manual exposure. As you shift your lens, the camera's TTL metering will be fooled. To avoid that, set an exposure for the primary image and leave it there. Think of that primary image as the center of the tic-tac-toe grid. Once you've set and photographed your principle composition, decide whether you want to move up and down in the center vertical axis of the grid or left to right across the horizontal axis. Rotate the lens so that the shift moves in the direction you want—either vertically or horizontally, because it can only move in one axis at a time. Release the shift lock and then rotate the knob that shifts the lens, let's say vertically as it was in the example shown. The view through the viewfinder changes to incorporate more of the ceiling. Once you've shifted the lens enough, lock it down and take a picture. Then release the lock and shift back down past the original view to expand the frame downward. Again lock it down and shoot another frame.

Digital Photo Tip Of The Week
Bear in mind, while the lens is likely capable of shifting quite far, at the extremes of the movement you're more likely to see vignetting and image quality issues as you approach the edge of the circle of light. To be sure to avoid these issues, limit your movements to as little as possible in order to get the shot. Canon's T/S lenses have red indicators on the lens that show how much shift is likely too much. Work within these limits and you're likely to be fine.

For me, I most often employ this technique when photographing architectural interiors, when I want to see more of the floor or ceiling as in the example here. Rise and fall (the proper term for vertical movements) make my 24mm tilt-shift lens behave more like a 20mm or even a 17mm in terms of the expanded coverage from floor to ceiling.

Once I've got my three images ready to be processed in the computer, I start by turning off any lens corrections and doing very little post processing to the raw files—and definitely nothing that can't be duplicated exactly from frame to frame. I want these files to be as straight out of the camera as possible, because straight out of the camera they should fit together pretty perfectly. I definitely want to avoid any sort of vignetting or other effects that treat each image differently at the edges. That would make the blend problematic where the images overlap.

Digital Photo Tip Of The Week
In Photoshop, you can use the Scripts function (under the File menu) to Load Files Into Stack, which will simply create a three-layered file with each image occupying one of the layers. That's my preferred approach, because then I can manually overlay each image to ensure they fit together seamlessly. The other method would be to allow Photoshop's Photomerge tool to try to automatically position and blend the image files. This could work fine for lots of purposes, but I've had enough trouble with funky blends and missed alignments that I just prefer the manual method, which is simple enough that it's really not much of a sacrifice.

Next, I change the Canvas Size in the Image Menu. From a horizontal canvas size of 12x20 inches, for instance, I would add to the top and bottom of the canvas to make a new image that's square (changing the height to 20 inches) or possibly even vertically oriented (making the height 22 inches or even more). Leave the anchor point in the center of the grid to maintain the primary image in the center of the canvas and click OK.

Next, turn off one of the layers—either the image that will become the top or the bottom of the frame—and work with the other one, ensuring that it's above the layer that will act as the primary image. Let's start with the top. Click the layer in the layers palette to activate it, and then use the arrow tool to click and drag it into place—or at least approximately into place. In order to align it perfectly with the layer below, change the upper layer's mode to Difference. In Difference Mode, when the pixels are perfectly aligned, they turn black. In this way you can click and drag or use the arrow keys to make fine adjustments and zoom in very close to check your progress. When the pixels are perfectly aligned it becomes quite clear. Once that's the case, change the layer mode back to normal, then repeat the process on the third layer—the one that will form the bottom portion of the new composite image. (You can also lock completed layers together so that you don't accidentally move them. Click the first layer you'd like to lock in the layers palette, then shift click the others. Once the layers are selected, right click on the layers palette and choose "Lock Layers.")

Digital Photo Tip Of The Week
Before flattening the layers, check the edges where the images overlap. If there are any issues that make the composite obvious, or subtly misaligned elements, I use a layer mask with a soft-edged brush to mask away the top layer and more seamlessly blend it into the primary image below.

In the end, I've created an image file that offers a wider angle of view than was possible with the 24mm lens I started with. My image's resolution has also gone from 20 megapixels to almost 33 megapixels. That's why this technique is so powerful. I may use it mostly on interiors, but it's equally useful for all sorts of subjects—so long as they're not moving. Landscapes are ideal candidates for this technique, as are still-life photographs. Don't forget that tilt-shift lenses are available in more than just wide-angle versions. Normal and telephoto tilt shifts can make this technique even more useful for a wider variety of subjects.

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