Focus Stacking in Landscape Photography

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When using telephoto lenses in landscape photography, the photographer sometimes runs into problems involving depth-of-field. Unlike portrait photography, in which a narrow depth-of-field is desirable, landscape photographers usually want a very wide depth-of-field, with as much in focus as feasible. But when shooting with telephoto lenses, depth-of-field tends to be restricted, even when stopped down. Take the above photograph. That was shot with a telephoto zoom lens at 90mm. Even though f8 was used, only the little tree in the foreground is in focus:

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The lighthouse is slightly out-of-focus. Now you could try to remedy this by stopping the lens down and shooting, say, at f16 or f22. Problem here is that diffraction tends to impact resolution if you stop down much past f8. Given that the lens I was using is not exactly a resolution warrior, I really didn’t want to stop the lens down past f8. But I would also like to get both the tree and the lighthouse in focus. Is this possible?

I took another image focusing on the lighthouse:

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Now the lighthouse is in focus, but the tree isn’t:

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There is a way, however, to get around problem: namely, focus stacking. Both Photoshop CS4 and CS5 enjoy this capability. For landscape photography involving longer lenses, it can prove quite useful. You first load the two (or more) images into a single file in Photoshop, with each image a separate layer. Make sure all the layers are selecting in the Layers palette and then go to the “Edit” menu and select “Auto-Align.” After this is accomplished, return to the “Edit” menu and select “Auto-Blend.” Photoshop will automatically mask the images in such a way as that everything will be in focus, as follows:

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Here’s another example. The first photo is focused on the background, the second on the foreground:

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And then the final result from focus-stacking:

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Incidentally, I would assume that focus stacking works best with lenses that aren’t “internal focusing.” The trouble with internal focusing lenses is that they change focal length when they focus, which could conceivably lead to issues when combining the files in Photoshop. I haven’t done any experiments as yet (most of my landscape glass are not internal focusing lenses), but as a new landscape zoom lens is arriving tomorrow that is, unfortunately, an internal focusing lens, perhaps I’ll run some tests. In any case, internal focusing lenses strike me as an example of mere engineering cleverness put forward at the expense of good sense, an unfortunate trend in a world that worships the latest technology and whatever is “new.”