Canon EOS mag

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Technique EF 40mm f2.8 STM lens
18 Reproduced from EOS magazine October-December 2012 Reproduced from EOS magazine October-December 2012 19
The EF 40mm f2.8 STM is the first Canon prime lens with stepper motor focusing
technology. It is known as a ‘pancake’ lens, because of the short lens barrel. And it is
more ‘standard’ than a 50mm lens. Andrew Gibson is impressed.
Standard lens
A pancake lens is a bewitching object. Small, light and unobtrusive, it
fits snugly in the palm of your hand or slips easily into your camera bag.
What’s not to love?
I’ve been keeping a covetous eye on the pancake lenses made for
mirrorless cameras for a while, so when Canon announced their EF
40mm f2.8 STM lens, I bought it. I wasn’t the only purchaser – the shop
assistant said six of the new lenses had been received from Canon and
they had sold fast – mine was the last remaining.
Why is this lens so popular? It’s partly the price – the retail price is
under £230. The build quality is excellent, better than that of Canon’s
least expensive lens, the EF 50mm f1.8 II (£129.99 RRP). The optical
quality is superb. But the appeal of this lens reaches beyond all those
things. It’s beautiful, simple and functional. Apple has been incorporating
these aspects into its designs for years. Now Canon has done the same
with the EF 40mm f2.8 STM pancake lens.
Actual size
The ideal walk-around lens
40mm is an interesting focal length. On the
full-frame EOS 5D Mark II it is a moderate wide-
angle lens – and barely that, considering a true
‘standard’ lens would have a focal length of
just over 43mm (based on the diagonal of the
image format). It feels very natural and is ideal
as a walk-around lens – wide enough to provide
an interesting perspective, yet not so wide that
exaggerated perspective is a problem.
A couple of factors piqued my curiosity.
1 On an APS-C camera a 40mm lens becomes
a short telephoto (the equivalent of a 64mm
lens on a 35mm camera) – ideal for portraits.
2 The minimum focusing distance is only
30cm. That’s close, especially when used with
an APS-C camera, and I wanted to see how
the lens performed with a close-up filter or
extension tubes.
Stepper motor technology
Stepper motors date back to the 19th century. The technology has come a
long way since then – making the motors smaller, quieter and faster. Your
flatbed scanner or inkjet printer probably use stepper motors. Canon is
not the first manufacturer to bring the benefits of stepper motors to lens
focusing, but it is the first to bring the technology to DSLR lenses.
A stepper motor converts digital pulses into mechanical rotation. One
complete rotation of the shaft is divided into a large number of small steps.
Each pulse rotates the shaft by one step and the position of the motor shaft
can be controlled without any feedback mechanism. A large number of
digital pulses give a very smooth rotation of the shaft. All this contributes
to fast and accurate autofocusing.
There are no contact brushes in the motor, giving the device a long
life. The motor is reliable, rugged and relatively inexpensive (though not
the cheapest option for lens focusing). It is also very quiet, making it ideal
when the lens is used on an EOS camera shooting movies as the built-in
microphone is less likely to pick up noise.
Actual size
Above The EF 40mm lens looks tiny on an EOS 5D Mark
II, but provides an impressive performance. The EF 50mm
lens is often called the ‘nifty fifty’. One internet user has
dubbed this new lens the ‘shorty forty’.
Right The EF 40mm lens is perfect for portraits (see
. The lens lets you get close enough to fill the
frame, but without introducing perspective distortion. The
f2.8 maximum aperture makes it easier to shoot indoors
without flash and helps to throw distracting backgrounds
out-of-focus.
EOS 5D Mark II, 1/125 second at f2.8, ISO 200.
ALL PHOTOS ANDREW GIBSON