A true macro lens is one that can create a life-size image – 1:1 magnification or greater. Canon offers a range of prime macro lenses with focal lengths from 50mm to 180mm. Most take you up to life-size magnification while one starts at life-size, rising to five times life-size magnification.
Macro lenses are not just for macro photography. Certainly this is what they’re designed for, but most focus to infinity as well, making them exceptionally versatile lenses that can be used for photographing far more than just fine detail.
The essential difference between a macro lens and an ordinary lens is that the optical elements of a macro lens can move over a greater range. This allows them to bring subjects at a closer distance into sharp focus.
If you compare two equivalent focal length lenses, for example, the EF100mm f/2 USM and the EF100mm f/2.8 Macro USM, you will see that the close focusing distance of each is very different. The macro lens can focus sharply on a subject just 31cm away from the lens, while the non-macro lens can only focus on a subject if it is 90cm away or further.
Being able to focus closer, the macro lens magnifies an image more. In this case, a subject 31cm away will be recorded as life-size. Compare this with the non-macro 100mm lens. A subject at its closest focusing distance will only be recorded as 0.14x the actual size. In other words, if the subject is 10cm long in real life, when recorded on film or on the digital sensor, it will only be 1.4cm long.
Traditional lens design uses a ‘focusing lens group’ to focus the lens. This usually comprises either the front lens element, or group of elements, or all of the lens elements, that move forwards and backwards to produce a sharp image.
However, moving the front lens elements or the whole set of elements around can affect optical performance, particularly at close focusing distances.
There are three EF100mm macro lenses. The older one, the EF100mm f/2.8 Macro was introduced in 1990 and is now discontinued. It followed the traditional method of lens manufacture, with the front elements performing the focusing. Although an excellent lens made from very high quality glass, it was superseded in 2000 by the EF100mm f/2.8 Macro USM. In 2010 an updated version of the EF100mm f/2.8 Macro USM lens, the EF100mm f/2.8L Macro IS USM, offered the same focal length and focusing abilities but added a Hybrid Image Stabilizer for handheld shooting.
The Hybrid Image Stabilizer unit is designed specifically for macro shooting. Instead of correcting only for angular movement, it also corrects for shift movements, which are much more prevalent when shooting close up to a subject. At normal distances the Hybrid IS offers 4-stops of image stabilisation. At 1:1, or life-size, it provides 2-stops of IS.
There’s little difference in the name, but the lens released in 2000 was given a USM tag to signify the inclusion of an ultrasonic motor. This is the high-speed motor that drives the autofocus, enabling the lens to focus quickly and quietly. Moving the front lens element – or indeed any lens element – is not easy, especially if you want to do it quickly. To overcome this problem, the new macro lens uses an inner focusing system.
As the name suggests, the inner focusing system moves one of the internal optical groups to achieve focus, as opposed to moving the larger front lens element group forwards. Not only is the internal optical group lighter, and therefore easier for the USM motor to move, but it also allows a closer minimum focusing distance.
Most usefully for macro photography, however, is that the lens released in 2000 does not change length as you focus. This may not sound important, but when you are working very close to a subject it is easy to get too close as you focus in, hitting your subject with the lens. The lens is also less likely to cast its own shadow over the subject. And because the lens does not get longer as you focus closer, its handling and balance is not affected at any magnification.