trueColors JULY 2011.indd - GMG Color

The digital
photography
resource
Tilt shift lenses:
perspective control
Tilt shift lenses enable photographers to transcend the
normal restrictions of depth of field and perspective. Many
of the optical tricks these lenses permit could not otherwise
be reproduced digitally, making them a must for certain
landscape, architectural and product photography. The first
part of this tutorial addresses the shift feature, and focuses
on its use for in digital SLR cameras for perspective control
and panoramas.
Overview: tilt shift movements
Shift movements enable the photographer to shift the location of the
lens's imaging circle relative to the digital camera sensor. This means that
the lens's center of perspective no longer corresponds the the image's
center of perspective, and produces an effect similar to only using a crop
from the side of a correspondingly wider angle lens.
Tilt movements enable the photographer to tilt the plane of sharpest
focus so that it no longer lies perpendicular to the lens axis. This produces
a wedge-shaped depth of field whose width increases further from the
camera. The tilt effect therefore does not necessarily increase depth of
field – it just allows the photographer to customize its location to better
suit their subject matter.
Concept: Lens imaging circle
The image captured at your camera's digital sensor is in fact just a central
rectangular crop of the circular image being captured by your lens (the
"imaging circle"). With most lenses this circle is designed to extend just
beyond what is needed by the sensor. Shift lenses, by contrast, actually
project a much larger imaging circle than is ordinarily required – thereby
allowing the photographer to "shift" this imaging circle to selectively
capture a given rectangular portion.
Lens shift LEFT RIGHT
Ordinary Camera Lens Lens capable of Shift Movements
Shift movements have two primary
uses: they enable photographers
to change perspective or expand
the angle of view (using multiple
images). The example shown
previously would be more useful
for creating a panorama since
the medium telephoto camera
lens created a flat perspective.
The shift ability comes with an
additional advantage: even when
unshifted, these lenses will typically
have better image quality at the
edges of the frame – similar to
using full frame 35 mm lenses on
cameras with a crop factor. This
means less softness and vignetting,
with potentially less pronounced
distortion.
Above: Nikon PC-E Nikkor 24mm
f/3.5D ED Tilt/Shift lens
On the other hand, a lens capable
of shift movements will need
to be much larger and heavier
than a comparable regular lens,
assuming the same focal length
and maximum aperture. Extreme
shift movements will also expose
regions of the imaging circle with
lower image quality, but this may
not be any worse than what is
always visible with an ordinary
camera lens. Further, a 24 mm tilt
shift lens is likely to be optically
similar to an ordinary 16 mm lens
due to a similar sized imaging
circle. This means that this 24 mm
tilt shift lens is therefore likely to be
surpassed in optical quality by an
ordinary 24 mm lens, since wider
angle lenses generally have poorer
optical quality.
Used with permission. Source: www.cambridgeincolour.com