It is now fairly common for DSLR photographers to produce very large images by combining (or “stitching”) multiple separate component exposures of a scene. With the right kind of subject (one that is fairly static) and careful technique this can be quite successful.

I’ve experimented in the past with stitched photographs. I’ve had some luck with hand aligning and masking individual photos, and I’ve played around with some third-party software designed for this task. I was pleased to find that a very competent stitching feature is now part of the newest CS3 version of Photoshop.

As an example of what you can do with this tool, I’ve uploaded a photograph I created earlier this summer. Shot at dawn at Thousand Island Lake in the Ansel Adams Wilderness Area, the photograph consists of five 12MP images. Click the thumbnail to see a larger version.

Greg writes:

I’ve enjoyed your photography that I’ve found on your three websites. I especially enjoyed your photos of the Sierras. While looking at your photo “RitterBannerEdizaFlowers2007_07_25.jpg” [see below] the question comes to mind, “How did he get everything from 12 inches to infinity in focus?”

Mounts Ritter and Banner, Ediza Lake. Sierra Nevada, California. © Copyright G Dan Mitchell.

(Greg also noted that current Canon EF lenses generally do not include a DOF scale.)

Thanks for writing, Greg.

The main technique in this photo is the use of a short focal length wide angle lens. It (along with similar photos in my gallery) was shot with the Canon EF 17-40mm f/4 L lens, which is an ultra-wide angle (UWA) lens on the full-frame Canon 5D. Such UWA lenses can produce an extraordinary depth of field – it may not be quite “12 inches to infinity,” but it is pretty close.

In addition, one can shoot at smaller apertures on a full frame DSLR compared to the crop sensor DSLRs. On a crop body you generally avoid apertures smaller than f/8 or so, especially if you are planning to make a large print. At smaller apertures, diffraction decreases the maximum sharpness of the image. You get greater depth of field, but the cost is that the sharpest portions of the image in the plane of focus actually become less sharp than at optimal apertures. With a larger sensor (or larger film), diffraction doesn’t become significant at f/8. I conducted some experiments with my L lenses and 5D and discovered that sharpness in the plane of focus is at least as good at f/11 as it is at f/8, and that focus plane sharpness at f/16 is virtually indistinguishable from f/8 and f/11.

So, by combining a very wide angle lens (I believe it was 17mm in this photo) with a very small aperture (f/16 most likely) and focusing just beyond the closest object in the frame, I can achieve very wide DOF.

There are a few other tricks that one can employ. Faced with scenes that have an extremely wide dynamic range, I often take two exposures with one set for the darker areas and the other for the bright areas. In a situation where the foreground is dark and the distant objects light, I can also slightly shift the focus between the two exposures. (I combine the two images in post-processing; this is more or less equivalent to using ND grad filters at the time of the exposure though it permits more flexibility at the expense of an extra exposure.)

– Dan

BTW, Greg also reminded me of an interesting SF Bay Area show that is about to close:

P.S. You had an earlier post about the Yosemite art exhibit at Stanford. I’d like to bring to your attention another Yosemite exhibit that is currently running through Aug 26 (ends soon!) at the Oakland Museum (http://www.museumca.org/). This is an enjoyable exhibition that covers the art of Yosemite from native american basketry, to mid-19th century painters, to photography; highly recommended!

A reader sent a nice message today which included the following:

I am always amazed by the detail of your photographs, the sharpness (I sometimes wish you’d elaborate a bit more on your settings of the shot ).

Thanks for the nice comment about detail and sharpness. Let me give a little overview of some of what I do. (Of course, to really see this you would have to look at a print. :-)

• Almost all of the photopraphs were made with either an 8 megapixel Canon 350D/XT or more recently with a 12 megapixel Canon 5D.
• I use high end Canon lenses – 17-40mm f/4 L, 24-105mm f/4 IS L, 70-200mm f/4 L, 50mm f/1.4.
• I tend to shoot at smaller apertures unless the depth of field requirements of the shot (or limited light and moving subjects) require larger apertures. For sharpness across the frame, I generally shoot at f/8 on the crop sensor 350D and at f/11 or f/16 of the full frame 5D.
• In most cases I shoot from a tripod and use a remote release and mirror lockup.
• I post-process photographs and appropriately “work” the images using methods comparable to those used by traditional film photographers (dodging, burning, contrast selections, etc.) and some that are available in Photoshop (localized levels, saturation, color balance, and others).
• I apply two stages of sharpening to the full size images. First I apply “smart sharpening” to produce the greatest micro detail, while being careful to avoid unnatural sharpening artifacts. Then I apply some unsharp masking to provide “local contrast enhancement.”
• After downsizing the images for posting here, I do one more subtle unsharp mask operation to slightly increase detail in the smaller .jpg versions posted on the web.

Whew!

And that’s only a general summary. Individual images require different processing and different techniques. For example, it would not have been appropriate to do a lot of sharpening in my recently-posted photograph of evening rain in Yosemite Valley. On the other hand, in order to produce the best image it is sometimes necessary to use even more extensive post-processing techniques, such as in recent photos of early morning on the floor of Yosemite Valley, where the scene had an extremely wide dynamic range.

I’m usually happy to explain more about a particular image if you are interested, so just ask! :-)
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