We’ll start by clarifying the definition of ‘macro’. True macro refers only to ‘life-size’ reproduction – which means a 1:1 reproduction (magnification) ratio. 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 – although it probably won’t fit onto a 4/3-inch type sensor; 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.
. 50-65mm – typically used for product photography (eg, jewellery) and small, non-mobile objects;
. 90-110mm – 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).
Many zoom lenses also claim to have ‘macro’ capabilities, although this is more of a marketing term than a true description of their capacities, because few of them can achieve reproduction ratios greater than 1:4 (one quarter life size). Tamron and Sigma each have a 70-300mm lens that claims 1:2 reproduction – but this is quite unusual.
A macro shot of Geraldton Wax flowers taken with a zoom lens with macro capabilities.
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 specialised and put in a special high-magnification category.
Alternatively, 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 reduced. Reversing rings, which allow 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.
Finally, if you simply want good close-up capabilities, use a compact camera and set the focus to the macro position. Compact digicams have an advantage over interchangeable-lens cameras for close-up photography because their smaller sensors provide a greater depth-of-field and allow a greater working distance for their reproduction ratios. Many models come close to a 1:1 reproduction ratio at shooting distances of just a centimetre or two.
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 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 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.
The table below provides a guide to the minimum working distances for some commonly-used macro focal lengths.
A good working distance is essential when photographing mobile animals that may be easily ‘spooked’. This shot was taken with a 180mm lens using an aperture of f/8 and ISO setting of 800 to obtain a fast enough shutter speed to avoid blurring due to subject or camera movement.
Depth-of-Field and Focusing
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 maximise 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.
Because depth-of-field is small, it’s essential to focus on the correct part of the subject. When the lens is focused just off this area, as shown in the picture on the left, the shot is unusable.
Check the background to the subject before taking the shot – particularly when you have stopped the lens down. If your camera has a depth-of-field preview button it will allow you to see if the subject is overwhelmed by background detail.
These two examples show the same subject with different backgrounds obtained by adjusting the camera angle. In each shot the lens aperture was f/5.6 but a change in the photographer’s position changed the distance between the subject and the background.
Bokeh can make a big difference to the attractiveness of close-up shots and it’s worth seeking out a lens that renders out-of-focus details smoothly. You can reduce the impact of a lens with rough bokeh by shooting at the widest aperture, although this will also reduce the depth of focus in the picture.
The image on the left was photographed with a 90mm macro lens using an aperture of f/2.8. The one on the right shows the change in depth of focus and bokeh resulting from stopping down to f/8.
Using a macro lens on a DSLR will allow a greater working distance and give some space to introduce additional lighting in the form of studio lights or additional flash units that can be triggered remotely from the camera’s flash. 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.
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.
Calculating Reproduction Ratios
Close-ups with Digicams
Such a short working distance will involve the same problems with lighting as you find when using a macro lens on an interchangeable-lens camera, and flash fill is impossible. You also encounter the same risks of ‘spooking’ small animals and insects. In addition, if the front of the lens touches the subject, flakes of pollen, dust or other materials could be transferred to the lens and they will prevent you from taking sharp pictures.
Some digicams allow users to shoot close-ups when the lens is at full tele zoom. The reproduction ratio is often significantly less than at the wide-angle position but you have the advantage of a much greater working distance. You may also be able to use the built-in flash for fill-in lighting.
Keep sensitivity settings low when shooting close-ups with a digicam because image noise will be more visible in out-of-focus areas. ISO 200 should be seen as the upper limit for all small-sensor digicams; ISO 50 and ISO 100 are the optimum settings.
A relatively large spider (roughly 2cm across the tips of the legs) photographed with a compact digicam. (Canon PowerShot G10, 30.5mm focal length, ISO 100, 1/80 second at f/4.5.)
Many digicams are limited to a minimum focusing distance of around 5cm, which is fine for close-ups of relatively large subjects, such as this Banksia flower, but doesn’t constitute macro photography. (Sony DSC-HX5V, 42,5mm focal length, ISO 125, 1/200 second at f/5.5.)
This is an article from Photo Review Magazine Dec-Feb 2010/11 Issue 46.