Because most consumers demand very compact, lightweight equipment, the majority
of lenses are designed with a relatively small aperture: f/4 to f/5.6, for example.
That makes sense because the same focal length with a wide aperture would be
larger, heavier, and more expensive due to the oversized optical elements and
barrel. Even so, many photo enthusiasts really appreciate an aperture of f/2.8,
available with some high-grade lenses, such as the two new Sigma models that
I tested. The primary advantage is the ability to shoot at faster shutter speeds
in low light or during sports events without the need to use higher ISO levels
that can degrade image quality. As a bonus, autofocus speed and reliability
in dark locations may also be better because more light reaches the AF sensor.
Although quite different in certain respects, the Sigma "digital only"
50-150mm f/2.8 zoom and the "multi-platform" 70mm f/2.8 Macro share
some attributes. The most noteworthy similarities include rugged construction
with metal barrels; digital ptimization (using unspecified technology) for high
sharpness/brightness across the frame; extensive use of super multilayered lens
coating to minimize flare and ghosting; and a remarkably high level of correction
for optical aberrations with several low dispersion glass elements. More importantly,
all of these features combine to make both Sigma lenses superior performers
in their categories.
Especially on a compact/lightweight Canon EOS Digital Rebel
XTi, the 50-150mm zoom never became a burden during an all-day
hike with my family. Far more portable than a multi-platform
70-200mm f/2.8 zoom, this smaller lens is equally desirable
in all respects, except for the shorter focal length. (Image
made at 150mm at f/5.6, using a 580EX flash unit and a super
multi-coated Hoya polarizer.)
All Photos © 2007, Peter K. Burian, All Rights Reserved
Sigma Zoom Lens
Roughly equivalent to the 70-200mm f/2.8 HSM zoom in terms of equivalent focal
length when used with an APS-C sensor, the APO 50-150mm f/2.8 EX DC HSM is a
miniature version of that multi-platform lens. It's 21 oz lighter but
just as rugged with a scratch-resistant metal barrel. It also features a wide,
rubberized focus and zoom ring, both with plenty of friction for a familiar
feel. This newer zoom does not accept a tripod-mounting collar, however, but
that's not a problem considering the modest size/weight. It's tiny
when compared to the 70-200mm f/2.8 zoom because of the shorter focal lengths
and because a "digital only" zoom does not need to project the larger
image circle required to fill a 35mm film frame. Naturally, this lens would
cause serious darkening of the edges of the frame if used on a 35mm SLR camera
or a Canon D-SLR with a larger than APS-C sensor.
Like its full-size sibling, this tele-zoom is equipped with a Hyper Sonic Motor
(HSM), an ultrasonic system that provides very fast, nearly silent AF operation.
Because HSM is compatible only with Canon, Nikon, and Sigma SLR cameras, Sigma
is making this zoom only in those three mounts. Even when shooting in AF mode,
manual focus is always available with HSM, allowing for slight touch-ups when
necessary. Note, too, that this lens also employs internal focusing. That helps
accelerate autofocus (because fewer lens elements must be shifted) and ensures
that the barrel does not extend or rotate; hence, a polarizing filter's
effect never changes while focusing or zooming.
Although it's priced to attract the serious photo enthusiast,
the Sigma 50-150mm f/2.8 zoom is a pro-caliber lens in all respects.
It proved to be an excellent choice for recording the models
during a bridal show with reliable tracking focus and high resolution
even at the wide f/3.5 aperture that I frequently used during
this event. (Location courtesy of the 2007 Burlington/Oakville
My favorite image from the bridal fashion show, this 10-megapixel
raw capture (using the 50-150mm zoom) made for a superb 13x19"
print. Don't mistake the blurring of the subjects behind
the point of focus for lack of resolution. That's simply
a sign of shallow depth of field caused by the use of a wide aperture,
f/3.5 in this case. (Location courtesy of the 2007 Burlington/Oakville
As the APO (Apochromatic) designation suggests, this zoom is exceptionally
well corrected for chromatic aberration, with four pieces of Special Low Dispersion
(SLD) glass. This combination causes all wavelengths of light to focus on the
digital sensor plane for really great image quality, particularly at wide apertures,
with very high sharpness and freedom from purple fringing around subject edges.
Super multilayered coatings on numerous elements minimize the risk of flare
and "ghosting" (reflections in the shape of the lens diaphragm)
caused by a highly reflective digital sensor. That feature, plus the deep lens
hood, also provides
great resistance to flare from external light sources, making for images with
Evaluation: While shooting stock photos using a Canon EOS Digital Rebel XTi,
I found this rugged but compact 80-240mm equivalent zoom to be ideal in every
respect. The combination of HSM focus motor plus wide maximum aperture (that
transmits a great deal of light to the AF sensor) definitely paid off. Even
in low light, the camera focused quickly and reliably; continuous tracking focus
was incredibly fast, too. As expected, this APO lens also proved to be outstanding
in terms of ultrahigh resolution and snappy contrast even in strong sidelighting.
All zooms produce some shading (darkening at the corners) but this one is surprisingly
well corrected; by f/4.5, edge brightness is excellent.
Like nearly all tele-zoom lenses, the Sigma 50-150mm lens produces
the very best image quality at the shorter focal lengths. And
yet, even at the 150mm end, sharpness is high across the entire
frame by f/4, impressive performance for a relatively affordable
pro-grade f/2.8 zoom. (Image made at f/4 at ISO 400, with a
Canon EOS Digital Rebel XTi and a super multi-coated Hoya polarizer.)
Optimal performance (superlative) was provided at f/5.6 and f/8 in the 50-110mm
focal length range, although I never hesitated to shoot at f/4. My best images
made for gallery-quality 13x19" prints. The wider f/2.8 aperture was useful,
too, for faster shutter speeds; resolution of fine detail is still high, particularly
around the central area of the frame. When using the 110-150mm range, it was
definitely worth stopping down to f/4, and to f/5.6 when maximum edge sharpness
was necessary. This is an incredibly fine showing in the 50-110mm range and
remarkably good at the longer focal lengths. Overall, the Sigma 50-150mm f/2.8
zoom is definitely of professional caliber. While this may not be a totally
fair comparison, I found this "digital only" zoom to be even better
than the highly rated multi-platform Sigma 70-200mm f/2.8 HSM Macro zoom, particularly
in terms of wide aperture image quality.
Sigma Macro Lens
A true macro lens capable of 1x magnification, the Sigma 70mm f/2.8 EX DG Macro
can reproduce a tiny subject as life-size on a 35mm film frame or a full-frame
digital sensor. Mount the lens on a digital camera with the more typical smaller
(APS-C size) sensor and it provides higher "apparent magnification."
This effect occurs because only a portion of the large image circle projected
by the lens is recorded by the small sensor. In other words, the field of view
is being cropped and that's reflected in the viewfinder. While that effect
is not produced by higher magnification, the subject does appear larger because
less of the scene is included in the image area.
Most of the "macro" designated zoom lenses can focus
close enough to provide 0.25x magnification (Photo A) but the
Sigma 70mm lens is capable of a full 1x magnification (Photo
B) when used with a 35mm SLR or a D-SLR with full-frame sensor.
This is a very rugged lens but it's not equipped with the Hyper Sonic
Motor, so it employs conventional autofocus. The optical formula boasts a Special
Low Dispersion (SLD) element plus two pieces of high refractive index SLD glass
to minimize chromatic aberration. Like all recent Sigma lenses, it benefits
from superior multilayered coating for remarkably effective flare control. At
first glance, this lens is quite compact but when set for the minimum focus
distance, the inner barrel does extend by 2", making the overall length
a full 5.76". That can be a problem in nature photography, because the
front element will be very close to the subject in high-magnification photography.
The lens hood is certainly unusual. Instead of attaching in a typical manner,
it screws into the filter threads of the lens; since the front of the hood is
threaded, you can still use a (77mm) filter.