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Tuesday, August 31, 2010

Control Your Depth of Field


Try the Focus Slice Auto-Align technique to get tack-sharpness from near to far

Labels: How-To



This Article Features Photo Zoom

Figure 8: A footbridge over a stream, Great Smoky Mountains National Park, Tenn. The scene was photographed with a 24mm lens using two focus slices. The posts and handrails in the foreground had to be carefully painted in to make sure the transition between the handrails in the two layers was sharp because the posts and handrails in the background were focused in the second layer.
The next step is to open all slices in Adobe Camera Raw or Lightroom and process the RAW images. When done, use the Select All and Synchronize features in Adobe Camera Raw to make sure all adjustments apply to all the slices and then save the slices in a Photoshop folder as 16-bit files.

First, open the Foreground slice in Photoshop. It can be confusing because Photoshop opens the Foreground slice that was opened first and labels it “Background.” Then, open the Horizon slice (for a two-slice image). Go to Window, scroll to Arrange, then click on Tile (Fig. 5). Click on the Move tool, highlight the Horizon layer, hold down the Shift key and place the Horizon layer on the Foreground layer. Photoshop labels this “Layer 1,” and it’s highlighted (Fig. 6). Delete the Horizon layer.

In the Layers palette, highlight both layers, go to Edit, click on Auto-Align Layers and check Auto, then OK (Fig. 7). In the Layers palette, highlight Layer 1. Go to Layer, then Layer Mask, Reveal All. In Set Background Color in the Tools palette, set the foreground color to black. The Horizon layer is on top, and we’ll paint in the sharp Foreground layer underneath. Expand the image to 100% and, with the Brush tool set at about 200 and Hardness at 0%, paint in the sharp foreground image underneath. To show where you’ve painted, use the Backslash key to engage the Rubylith mask of the active channel, which is shown as a red mask. This also is convenient for moving to the next quadrant for continuing the painting (Fig. 9). Clicking again on the Backslash key removes the red mask. The final sharp image was shown in Figure 4.


Figure 9: To follow the progress of the painting process, the Rubylith mask of the active channel can be engaged by using the Backslash key, revealing the red mask where painting has occurred. The mask can be removed using the Backslash key.
Completing a sharp image for the ice fields in Door County was fairly simple and a straightforward painting exercise because the foreground and background are distinctly layered. The image of the path in the Great Smoky Mountains National Park (Fig. 8) is more difficult because the posts in the handrails project vertically. This is an image where a tilt/shift lens wouldn’t offer a great advantage because the posts extend well above the Scheimpflug wedge of focus. The near posts focus as a foreground layer, but the posts and handrails at the back of the bridge are focused in the second layer, or horizon layer. The foreground posts and handrails also are surrounded by the vegetation in the horizon layer in the distance. Therefore, the foreground posts need to be carefully painted in with the image expanded to 100% with careful attention paid to the transition zones in the handrails, but the procedure used is exactly as described for the ice field scene.


In conclusion, if a scene requiring great depth of field can be captured using a tilt/shift lens, that would be ideal because the scene can be photographed with a single exposure. Or if the desired depth of field can be accomplished without artifacts with the simpler and faster Helicon Focus, that would also be preferable in the interest of convenience. However, Focus Slice Auto-Align, a procedure made possible by digital technology, is still the most accurate and precise procedure for controlling depth of field. And when no simpler technique will work, this is the procedure of choice.

To see more of Willard Clay’s photography, visit www.willardclay.com.

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