What are Macro lenses?
A macro lens is a lens that is manufactured in a special way, to make the lens especially suitable for up-close photography.
'Normal', non-macro lenses are designed so the sharpness and contrast of the lens gets better the closer you focus to infinity. The thinking behind this is that most of the photos you take will be towards the end of the focusing range. With a macro lens, however, this is the other way around. Most macro lenses are quite good on the longer focal ranges, but they really excel on sharpness, contrast, and overall photo quality in the other extreme of the focus range!
In practice, a macro lens means that you can take pictures at shorter focal distances than with 'normal' lenses. The most extreme macro lenses can focus down to 2 cm (approx 0.8 inch). these kinds of lenses are often found on digital cameras (in particular the models from Casio and Nikon), but this isn't necessarily the best way forward for Single Lens Reflex (SLR) cameras. Instead, Macro lenses are usually lenses that have a longer focal length, combined with the ability to focus at relatively short distances - typically 1 meter or closer.
Types of macro lenses
Macro lenses are available with focal lengths from around 50mm to as high as 300mm. Shorter focal lengths can give higher sharpness, but you have to get really close to get a full macro reproduction of your photo. In particular, if you are photographing insects or animals, you are out of luck with a 50mm macro lens: in order to be able to focus at such magnification, you are practically touching the subject, and the butterfly will be long gone by the time you trip the shutter. In addition, the lens itself is likely to be casting a shadow on what you are trying to photograph, which makes things more difficult.
Longer focal lengths, then, make a lot of sense. There are fine 180mm macro lenses out there, but you then experience another problem: you are starting to lose a lot of light due to the way the lenses are designed, and hand-holding the lens becomes more difficult. Many photographers find that a 100mm macro photo lens is the way forward It is no coincidence that most camera systems have a 100mm macro lens in their arsenals: Canon has the excellent Canon 100mm f/2.8 Macro USM, Nikon has the mighty fine 105mm f/2.8D AF Micro-Nikkor, and in addition, third-party lens manufacturers such as Sigma and Tamron have a series of macro lenses that cover the whole range from 50 – 300mm, all with full macro capabilities.
Price-wise, macro lenses are usually more expensive than their non-macro counterparts. On the other hand, they are usually of significantly better quality. Even if you never plan to do any macro photography it's worth considering a macro lens if you are in the market for a zoom lens.
Why use a macro lens?
More than anything else, a dedicated macro lens offers you the flexibility of being able to do macro photography on a whim – the lens you bring with you will be good enough to photograph anything you come across. If you were to go on safari on a budget, for example, it would be highly advisable to take something like the Sigma 70-300mm APO DG MACRO lens with you.
Not only do you get the flexibility of a good quality tele-zoom lens, but the Macro function is available at focal lengths of above 200mm, allowing you to focus at distances down to 95cm, for reproductions of 1:2. At around $220, it's an absolute bargain!
Pure macro lenses
In addition to all-round lenses that are particularly good for macro photography, there are a few very special lenses out there that are particularly built for macro photography.
The Canon MP-E65 is widely recognized as being one of the best specialized lenses for macro photography out there. MP-E65 is a unique manual-focus lens designed exclusively for macro shooting, at magnifications starting at 1:1 and going all the way up to 5:1. That means at its maximum magnification, you can fill a 35mm frame with a grain of rice
The lens comes with all the strengths of using bellows and reversing rings, but keeps full TTL metering. For all its good qualities, this lens is useless for anything but macro photography, and at around $750, it is rather pricey, as well. However, if you are serious about extreme macro photography, this lens is the ultimate match of ease-of-use, photo quality and incredible magnification.
This write-up an adapted extract from my upcoming book on macro photography.