Macro lenses are designed to focus much closer than a normal lens. This can create some problems photographers need to be aware of with respect to camera-to-subject distances and the risk of blocking light from reaching the subject.
An example of the creative use of the shallow depth of field of a 60mm macro lens on an APS-C DSLR. (Source: Tamron.)
Many zoom lenses claim to have ‘macro’ capabilities, although this is more of a marketing term than a true description of their capacities. Some digicams include ‘macro’ focusing modes that can capture sharp images of subjects as close as one centimetre from the front of the lens. But few of these can achieve reproduction ratios greater than 1:4 (one quarter life size).
Using macro lenses successfully requires an adequate working distance between the front of the lens and the subject. As a rough guide, the longer the focal length of the lens, the greater the working distance it provides.
True macro lenses can reproduce subjects at life size on the image sensor. (Taken with a 60mm macro lens on an Olympus OM-D camera.)
The closer you get to the subject, the more likely you are to encounter the following problems:
The subject gets ‘spooked’ and disappears. (Scientists often chill their subject before a shoot ““ but it requires just enough cold to slow the creature down without making it torpid or killing it).
The lens shadow interferes with the subject and there’s not enough room to introduce additional lighting.
Focusing is difficult because depth-of-field is very restricted. The autofocusing system will probably hunt for focus and, if you’re hand-holding the camera, it’s difficult to keep it steady enough to lock onto the subject. A tripod is useful for manual focusing but, even then, finding the focus point becomes more difficult the closer you are to the subject. If your subject is very mobile it will probably have moved on before you’ve set up the camera.
Choosing Macro Lenses
Specialised macro lenses are available to suit all DSLRs and some compact system cameras (CSCs). Options for DSLRs with 36 x 24mm sensors include:
30-60mm ““ typically used for product photography (e.g. jewellery) and small, non-mobile objects;
65-105mm ““ the standard macro focal length range; ideal for photographing flowers, insects and other small objects;
150-200mm ““ a better option for mobile insects and other small animals because it provides more working distance.
This shot illustrates the very shallow depth of focus that characterises true macro photography. (Taken with a 180mm lens on a camera with a 35mm sensor; 1/250 second at f/4.)
For DSLRs with APS-C sized sensors, the range of dedicated macro lenses is restricted to focal lengths between 40mm and 100mm. Allowing for the typical 1.5x and 1.6x crop factors, the following options are available:
40mm for product photography and small, non-mobile objects;
60mm for flowers, insects and similar small objects;
85-100mm for mobile insects.
Owners of M4/3 CSCs can only choose between 45mm and 60mm lenses, which provide the equivalent of 90mm and 120mm in 35mm format, respectively.
This picture of a small, colourful lizard, illustrates the shallow depth of field that comes with close-up shooting, even outside the true macro range. (Taken with a 60mm macro lens on an Olympus OM-D camera.)
Macro lenses need not be particularly fast because they are used at camera-to-subject distances that produce a restricted depth-of-field with normal aperture settings. In fact, many photographers stop down to f/5.6 or smaller apertures in order to have enough of the subject sharply imaged. It’s more useful to concentrate on working distance, ergonomics and stabilisation, and whether the lens is easy to hand-hold and adjust on the camera you have in mind.
Tamron’s SP AF 60mm f/2 macro lens combines extended depth of field control with low-light shooting capability and a good working distance on DSLRs with APS-C sized sensors. (Source: Tamron.)
The Olympus M.Zuiko Digital 60mm f/2.8 macro lens can focus to 19 cm from subjects. It is also weather sealed, an advantage for outdoor photographers.
There are other ways to achieve similar magnifications to true macro lenses, although they aren’t necessarily as easy to use and they may compromise image quality.
You can increase the distance between the lens and the sensor by attaching either extension tubes or extendable bellows to the back of the lens. This enables the lens to focus closer and provides greater magnification of the image. However it also reduces the amount of light transmitted to the sensor and may make accurate focusing difficult. Higher ISO settings will probably be required.
Fitting a close-up lens to the front of the camera’s lens is another, relatively inexpensive, option. Unfortunately most such lenses suffer from chromatic aberration and reduced sharpness.
Reversing rings, which allow lenses to be fitted wrong way round, can also produce up to 4x magnification. But they may be difficult to find for modern cameras that rely on electronic contacts for focusing and metering.
The closer you shoot and the more the subject is magnified, the smaller the depth-of-field in the subject. The size of the sensor can also influence depth-of-field. If you photograph the same subject so it occupies the same percentage of the sensor’s height with a 36 x 24mm DSLR camera and a M4/3 camera using the same lens aperture, the camera with the smaller sensor will produce noticeably greater depth-of-field. Some subjects require as much of the subject as possible to look sharp. For others, it’s best to have the main subject differentiated from a blurred background. The subject usually dictates which strategy to adopt.
Stopping down the lens is the best way to maximise depth-of-field. But since all lenses are diffraction-limited, a point will come where image sharpness will deteriorate. Avoid using the smallest aperture settings.
Make sure you focus on the most important part of the subject. For shots of insects and other small animals, the eye is usually the key point of focus; for flowers, the entire flower head works best for moderate close-ups, while the reproductive parts (stamens, pistil) are best for extreme close-ups.
An example of the use of the shallow depth of field to isolate a subject, taken with a 90mm macro lens on a 35mm DSLR. (Source: Tamron.)
It can be difficult to ensure close subjects are evenly ““ and adequately ““ lit when shooting close-ups. This is particularly true with shorter lenses, where on-camera flashes can have their light interrupted by the lens barrel.
While artificial lights can be used, they introduce a few problems. Flash units can be too harsh, while studio lights can be cumbersome and difficult to set up. Ring lights, which encircle the front of the lens with white LEDs or tiny flash tubes, can provide evenly-balanced lighting at close distances. But they tend to ‘flatten’ the subject, even with a good working distance. LEDs on adjustable arms let you control the angle and intensity of the light very precisely.
Diffusers and reflectors can be used to re-direct the light onto close subjects. ‘Bouncing’ the flash light off a reflector softens its effect and reduces the chance of specular reflections. Some experimentation is required to achieve success.
A diffused flash was used with -0.7EV exposure compensation to balance the light on this close-up shot, taken with the 300mm focal length on a ‘macro zoom’ lens.
Other Applications for Macro Lenses
Macro lenses aren’t just for close-ups; many photographers prefer them as portrait lenses, particularly those with focal lengths in the 80-105mm range (35mm equivalent). All macro lenses are fully functional at their prime focal length, which means those with shorter focal lengths can be used for landscape photography, while longer focal lengths can work well for capturing sports action.
Many macro lenses have very low levels of rectilinear distortion, which makes them useful for some kinds of architectural photography. Stabilisation is also common in recently-released macro lenses, which extends their use in poorly lit situations when short exposure times are required.
Macro lenses can also be used to shoot close-ups outside the macro range. This shot was taken with a 90mm macro lens on a camera with an APS-C sensor using an aperture of f/14 to maximise depth of field.
Excerpt from Lenses Guide.