Taking the macro view

A 60mm macro lens on a M4/3 camera was used for this shot, which is roughly half life size. With a 35mm equivalent focal length of 120mm, this lens provided plenty of working room for taking the shot without disturbing the subject.

Most photographers enjoy shooting close-ups, whether it be of flowers, insects, jewellery or other small objects. But when the subject is really small, it can be difficult to focus on it with normal lenses, which drives them to investigate macro lenses.

There’s a lot of misunderstanding about what constituted a ‘macro’ lens. Many zoon lenses also claim to have ‘macro’ capabilities, although this is more of a marketing term than a true description of the capacities because few of them can achieve reproduction ratios greater than 1:4 (one quarter life size). Some digicams include ‘macro’ focusing modes that can capture sharp images of subjects as close as one centimetre from the front of the lens.

True macro capabilities require the lens to be capable of 1:1 reproduction. In other words, an object that is 20mm high (or wide) will be reproduced at the same size (20mm) on the image sensor. It doesn’t matter how large or small that sensor is; the magnification ratio is totally independent of sensor dimensions. Half life-size reproduction ““ or a 1:2 reproduction ratio ““ is often included in the ‘macro’ category, although it’s not true macro.

Lenses that provide a 2:1 reproduction ratio ““ or greater ““ also qualify as macro lenses because they reproduce subjects at twice life size (a 20mm long object is magnified to 40mm on the sensor). These lenses are usually highly specialized and put in a special high-magnification category.

True macro lenses are capable of 1:1 (‘life size’) reproduction, independently of the dimensions of the camera’s image sensor.  

Macro Lenses

Specialised macro lenses are available to suit all DSLRs and some compact system cameras (CSCs). The focal length of macro lenses ranges from 30mm to 200mm, and different types of cameras with different-sized sensors will require different macro lenses. The range of focal lengths available is restricted for cameras with sensors smaller than ‘full frame’ (36 x 24mm).

Options for DSLRs with 36 x 24mm sensors include:

• 30-60mm ““ typically used for product photography (eg, 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 (see below).

For DSLRs with APS-C sized sensors, the range of dedicated macro lenses for the smaller format 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 Micro Four Thirds CSCs have very few focal length choices, with only 45mm and 60mm lenses available so far. These provide the equivalent of 90mm and 120mm in 35mm format, respectively.

This shot was taken with a 180mm macro lens on  an APS-C DSLR camera with a crop factor of 1.6x. The 288mm equivalent effective focal length and the long working distance were necessary to photograph this tiny spider, which was just under one centimetre which was a 1/800 second exposure taken at f/4 with ISO 800 sensitivity.  

Alternatives

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. However, most such lenses suffer from chromatic aberration and sharpness is also produced. Reversing rings, which allows lenses to be fitted wrong way round, can also produce up to 4x magnification. However, they may be difficult to find for most modern cameras that rely on electronic contacts for focusing and metering.

Working Distance

It’s essential to have a good working distance between the front of the lens and the subject when shooting close-ups, particularly if your subjects are animals (including insects and arachnids. As a rough guide, the longer the focal length of the lens, the greater the working distance it provides. The closer you get to the subject, the more likely you are to encounter the following problems:

1. The subject gets ‘spooked’ and disappears. (Scientists often chill their subjects before a shoot to prevent this from happening ““ but it requires care to apply just enough cold to slow the creature down without making it torpid or killing it.)
2. The lens shadow interferes with the subject and there’s not enough room to introduce artificial lighting. Flash units can be too harsh, while studio lights add unwanted heat. Ring lights tend to ‘flatten’ the subject, even when there’s enough working distance to use them.
3. Focusing is difficult because depth-of-field is vey 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 for focus 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. Furthermore, if your subject is very mobile (for example, a butterfly or bee) it will probably have moved on before you’ve set up the camera and the shot will be missed.  

Depth-of-Field and Focusing

The closer you shoot and the more the subject is magnified, the smaller the depth-of-field in the subject. This issue is particularly important because the size of the imaging area (sensor) can 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 in the subject.

For some subjects, you may want to have as much of the subject as possible looking sharp. For others, it’s an advantage 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 maximize depth-of-field. But be aware that all lenses are diffraction-limited; a point will come where image sharpness will be noticeably reduced.

When shooting with a shallow depth-of-field, it’s important to focus on the correct 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.  

A 50mm macro lens used for portraiture on an APS-C DSLR camera with a crop factor of 1.6x. The exposure was 1/100 second at f/5.6 with ISO 400 sensitivity.  

Stabilisation

Ideally, close-up shots should be taken with the camera mounted on a sturdy tripod. But this situation tends to work best when the subject is static or slow moving, or when you can predict where it will settle and remain long enough for you to take the shots.

With many moving subjects, hand-holding the camera is the only way to keep track of the subject. This is where stabilisation becomes important.

It doesn’t matter whether stabilization is built into the lens or the camera. What’s important is that it provides enough shake correction to enable you to see stead images in the camera’s viewfinder and capture blur-free shots.

Stabilisation is essential for close-ups because magnifying the subject will also amplify the effects of any camera shake. A hand-held shot taken with a 100mm macro lens on an APS-C DSLR camera. The camera-to- subject distance was 340 mm. The exposure was 1/250 second at f/7.1 with ISO 800 sensitivity.  

Lighting

It can be difficult to ensure close subjects are evenly ““ and adequately ““ lit when shooting close-ups. This is particularly true with shorter lenses, which don’t provide enough working space for additional lighting. In such situations, an on-camera flash will have its light wholly or partially cut off by the lens barrel.

Ring lights or ring flashes ““ which encircle the front of the lens with white LEDs or tiny flash tubes ““ can provide evenly-balanced lighting at close distances. LEDs on adjustable arms let you control the angle and intensity of the light very precisely.

Diffusers and reflectors are available for many external flash units. They can be used to re-direct the light onto close subjects. Home-made equivalents can be made from white cardboard, plastic or Styrofoam. ‘Bouncing’ the flash light off a reflector softens its effect and reduces the chance of specular reflections. Some experimentation is required to achieve success.

Other Applications for Macro Lenses

Macro lenses aren’t just for close-ups; manly photographers prefer them as portrait lenses, particularly those with focal lengths in the 80-105mm range (35mm equivalent). These lenses are fully functional at their prime focal length, which means those with shorter focal lengths can be used for landscape or architectural photography, while longer focal lengths can work well for capturing sports action.

A 60mm macro lens used for landscape photography on an M4/3 camera. The exposure was 1/160 second at f/11 with ISO 200 sensitivity.

Excerpt from  Photo Review Issue 61

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