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How Shift Lenses Change your Life
Shift lens documentation should tell you how much they shift. Let's look at the Canon TS-E 24mm/3.5L.
Like the other TS-E lenses, it shifts up to 11mm. This is the distance the lens elements move up, but that
also means the image moves exactly that much on the film. Since film images are upside-down, moving
the lens up moves the image down. This means... fewer parking lots and hot dog stands. And you can go
back to your original vantage point and get a bigger image.
How Close?
How far from your target do you need to be to get the desired shot without twisting the perspective?
Believe it or not, no trigonometry is needed. It depends on the height of the target above your eye level,
the height of the film above the centerline (red, above), and the lens' focal length.
Distance / TargetHeight = FocalLength / HeightAboveCenterline
Using that, solve for anything if you know the other three. In practice, you know the focal length and
height-above-centerline numbers exactly, or can dial in the height-above-centerline you need with a shift
lens. Distance may be harder to estimate, and height can be tricky. With buildings, you can usually guess
5 meters or 15 feet per story for commercial structures.
For now, this can help you picture what shots a given shift lens lets you take. For instance, since the
height-above-centerline is 12mm for a normal lens and twice that (well, 23mm) for the TS-E lenses with
maximum shift... we can get twice as close to our target. Or, shoot a target twice as tall. Or use twice the
focal length (say, the TS-E 45mm instead of a normal EF 24mm).
Later, on a shoot, this can avoid a certain amount of trial-and-error. For instance, say you have a 24mm
lens with 11mm of shift, and a four story building on a city street. You can back up to 65 feet away from
your 60 foot target. The formula says 65/60 = 24/X. X is about 22mm. You know that's right at the limit
of your shifting and the corners may darken somewhat. On the other hand, you not to even bother
getting your 1.4x TC out unless a vertical composition would work (vertically, 65/60 = 36/X, X would
be 33.3mm, and a you could get a maximum height-above-centerline of 18mm + 11mm x 1.4, or
33.4mm).
Drawbacks
When maximum shift is employed, shift lenses (with their unnaturally wide field of view) can show
some light falloff in the corners, due to basic optical properties. In addition, even the widest filters may
be visible in the corners of the shot. Smaller apertures typically fix the first problem but accentuate the
second. Hopefully you have the option of backing away from your target and reducing shift slightly. If
not, consider using an auxiliary filter holder instead of screw-on filters.
There are not yet any auto-focus shift lenses, even the Canon TS-E lenses with the auto-focus mount.
Some shift lenses are a bit more primitive, making you stop down manually before shooting. This will
http://www.photo.net/photo/canon/tilt-shift (3 of 9)7/3/2005 2:24:04 AM