Canon EF 100/2.8 Macro USM Lens Review
by Philip Greenspun; created February 2008
A 100mm macro lens has long been the standard for photographers using
full-frame cameras. The magnification of the 100mm lens provides
sufficient working distance from most subjects and does not add a lot
of weight or bulk compared to shorter macro lenses.
This is an extremely sharp portrait lens that focuses down to 1:1,
i.e., you can photograph an object as small as the 24x36mm sensor in a
full-frame camera or the 15x23mm sensor in a Digital Rebel. The front
element of the lens will be about six inches from the subject when
focussed down to 1:1.
The Canon 100/2.8 Macro USM is available from
amazon.com, $469.
Optics
The lens design is of medium complexity, with 12 elements of glass
arranged in 8 groups. The same arrangement of glass that produces
sharp images at infinity will not produce optimum results focussed
close. Consequently, three of the 12 elements are in a "floating
group" that moves as the focus is adjusted, i.e., the optical formula
of the lens changes as the lens is focussed from infinity down to 1:1.
Construction
Focus is via an ultrasonic motor, which provides for very fast
autofocus and full-time manual focus. The lens includes a switch to
limit the autofocus range to 0.5 meters so as to avoid slow
back-and-forth hunting with non-macro scenes. More unusually, the
focus mechanism is entirely internal. The front filter does not
rotate and the lens does not extend, even when going from infinity all
the way out to 1:1.
The lens takes 58mm filters and a very deep ET-67 circular hood that
bayonets on to the outside. For easy removal and reinstallation of
the lens cap with the hood in place, it is best to get a lens cap with
center releases, such as the Tamron (available from B&H Photo). A
tripod collar, denoted "Tripod Mount Ring B", is sold separately, but
should not be necessary with the beefier Canon bodies.
Weight is 21 oz. or 600g.
f/8 and be... out of focus
The young photographer asks the veteran for advice on how to take
pictures. "f/8 and be there," is the standard answer, but it isn't a
very good one for a 100mm macro lens. Depth of field at 1:1
magnification at f/8 is about 1mm, i.e., not sufficient unless the
subject is flat and the lens is precisely orthogonal to the subject
plane.
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Image at left: f/8
Image at right: f/16
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For most practical macro purposes, life starts at f/11 and gets
smaller from there. Here is the same subject at f/11, f/22, and f/32.
Notice how the tail and wingtips of the airplane come into
progressively sharper focus. Depth of field at f/32 should be
approximately 4mm, still not much, but viewers of macro images are
accustomed to selective focus.
f/32 and be unsharp
If good depth of field is the goal, why not set the lens to its
minimum aperture of f/32, use a big strobe or tripod and long exposure
time, and get as much depth of field as possible? Diffraction.
Photographing objects through a tiny hole, such as a lens's minimum
aperture, creates a somewhat fuzzy image due to diffraction.
Why mention diffraction in a review of this specific lens?
Diffraction is a more serious problem with macro photography than with
general purpose photography. With macro, one is more likely to
require very small apertures to obtain sufficient depth of field.
What's worse, at high magnifications, the effective aperture becomes
ever smaller. For example, at 1:1, the 100/2.8 Macro USM might be set
to f/32 but in terms of the amount of light transmitted and the
diffraction, it is functioning as though it were set two f-stops
smaller, i.e., f/64.
What's wrong with f/64? A lot of 8x10" view camera photographers use
f/64! Keep in mind that the 8x10" view camera photographer is likely
using a 300mm lens and that f-stops are ratios. An f/64 aperture on a
300mm is much wider than an f/64 aperture on a 100mm lens.
Here is some printed text at f/11, f/16, f/22, and f/32. The
magnification was 1:1 and light was from a Canon MR-14EX ring light.
Click to get larger versions so that you can see how the text becomes
fuzzier and lower contrast at f/32.
Good for eBay?
Sure. Get a light tent from www.ezcube.com, a couple of EX
strobes and a wireless controller, and you're all set. Here are a
couple of examples taken with just a simple Canon macro flash:
Good for portraits?
A 100mm lens set to f/2.8 sounds more or less ideal for portraits.
Does that make the 100/2.8 Macro USM a great portrait lens? Not quite.
For its popular portrait lenses, e.g., the 85/1.2, 85/1.8, 100/2, and
135/2, Canon puts a lot of effort into making the background blur
("bokeh") pleasing. This lens is not going to render out-of-focus
highlights as smoothly as a lens specifically designed for portraits.
Nor is the extra sharpness of this optic necessarily welcome by
subjects, unless the goal is a reference image prior to dermatological
surgery.
How does it work on a small sensor body?
On a small sensor body, such as a Canon EOS 40D, $1140 (review),
this lens works the same as a 160/2.8 macro lens would on a full-frame
camera, with the exception of more depth of field for any given
aperture (explanation). For
taking photographs of skittish insects, this would be an excellent
choice on a small sensor body.
Killer Accessory
The most useful accessory for this lens is a Canon macro flash.
Alternatives
The superb Canon EF-S 60mm f/2.8 Macro USM, $383 (review) on a small sensor body,
such as one from the Digital Rebel series, produces the same working distance
and magnification as the 100/2.8 on a full frame body.
On a full-frame body, here are the main alternatives:
Sigma, Tamron, and Tokina all make fixed focal length macro lenses in
the 90-105mm range. Optically these are very high quality, but they
lack the ultrasonic motor and internal focus of the Canon. Moreover,
the third-party lenses are not significantly cheaper.
Conclusion
Canon delivers everything that a photographer could want in a 100mm
macro lens: ultrasonic focus motor, internal focus mechanism,
non-rotating front element, floating optical group for consistent
image quality at different magnifications, rugged construction, and
reasonable price.
Where to Buy
You can get the Canon 100/2.8 Macro USM overnight from
amazon.com, $469.
More
Examples
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