Don’t expect to get everything sharp when using a
macro lens!
When you’re shooting at the minimum focus distance, depth of
field is extremely small. For example, with a 100mm lens on an APS-C camera,
it’s just 0.6mm at an aperture of f/2.8, so only areas that are within 0.3mm in
front of or behind the focus point will be rendered sharply. Even at f/11, the
depth of field is only 2.6mm.
Shallow depths of field aren’t too much of a problem when
shooting flat two-dimensional objects, but things get tricky in 3D. Because
focusing is so critical, you’re usually best off switching to manual focus, so
you can focus on exactly the part of the object you want to be sharp. Fixing
the camera in place and using Live View is helpful, as you can select a
magnified view on the camera’s LCD for high-precision focusing.
When you’re
photographing three-dimensional objects, the shallow depth of field from a macro
lens can cause problems
Sigma 50mm f/2.8 EX DG Macro
About the same size and weight as the diminutive Canon EF
50mm ‘Compact Macro’, this Sigma is similarly ideal as a lightweight prime lens
for general purpose shooting. For macro work, it has more potential than the
Canon, as it delivers a full 1.0x maximum magnification compared with the
Canon’s 0.5x. It’s not an internal focus lens and, like the Canon 50mm, it
features a magnification scale on its extending inner barrel. Here the display
is accurate, however, whereas the Canon’s scale doubles up magnification
factors.
Sigma 50mm f/2.8
EX DG Macro
The basic micro-motor autofocus mechanism is a little shrill
and sluggish but, unlike many macro lenses of around this focal length, there’s
a focus limit switch thatworks either side of 25cm. This really speeds up
autofocus performance in tricky conditions, where the lens might otherwise hunt
between infinity and its closest focus distance.
We were very impressed with the levels of sharpness, all the
way from its maximum aperture of f/2.8 to f/32. You can go even smaller, to a
tiny f/45 aperture, but in this case image quality drops off very noticeably.
For the price, this Sigma really is an over-achiever that’s equally useful as a
standard prime lens.
|
Verdict
·
Price: $350 ·
For: Small, light and versatile, with a reassuring build
quality ·
Against: No internal focusing means an extending front element
|
Sigma 70mm f/2.8 EX DG Macro
The design of the Sigma 70mm looks very similar to the
smaller 50mm version, although this lens lacks the antiquated aperture ring
sported by its smaller sibling. That’s no great loss anyway – lens-based
aperture rings are redundant when using Canon D-SLRs, as apertures are set via
the camera instead.
Sigma 70mm f/2.8
EX DG Macro
The focus limit switch works the same way as on the Sigma
50mm, but this time it locks focusing either side of 45cm instead of 25cm.
That’s fair enough, as the longer focal length of the 70mm lens means its
closest focus distance is 25cm anyway. There’s very much more travel at the
short end, however, when the focus range is locked. Manual focusing is smooth
and precise, although there’s no full-time manual override. The autofocus is
quite sluggish, and our review sample suffered from some nasty vibrations towards
the closer end of the focus range.
Optical quality proved very good, with plenty of resolving
power even at the largest aperture of f/2.8. This is also true at the smallest
aperture of f/22, although it’s worth bearing in mind that most macro lenses
stop down to f/32, and the Sigma 50mm and 105mm lenses close all the way down
to f/45.
|
Verdict
·
Price: $470 ·
For: Good optical performance, precise manual focus ring ·
Against: Slow noisy autofocus, nasty vibrations at the short
end
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