What is the best lens for insect macrophotography? I am asked this question every now and then, and the answer is always: “It depends.” The choice of your macro lens in nature photography depends on which aspects of your subject interest you the most.
True macro lenses come in different focal lengths, but they all have in common the ability to capture the subject with the magnification ratio of at least 1:1. This means that an insect 35 mm long will be represented on the sensor or film (the what now?) by an image that is 35 mm long; in other words, it will completely fill the frame. Most digital cameras have “cropped” sensors, which are smaller than the traditional 35 mm frame size that defined modern photography. This results in an image that appears larger than one captured on a “full frame” camera; for all intents and purposes, this gives you more magnification power from the same lens. Many lenses are marketed as “macro”, but if their maximum reproduction ratio is less than 1:1, then they should be considered “close-up”, and not true macro lenses (e.g., the popular Canon EF 50 mm f/2.5 Compact Macro has the magnification ratio of only 1:2.) When buying a new macro lens, always check its reproduction ratio – it should be 1:1 (=1.0x), or higher.
Once you have a true macro lens, its focal length becomes very important. The shorter the lens, the closer you need to get to your subject in order to achieve a full magnification effect. For example, a 50mm needs to be approximately 15 cm away from the subject (the exact focusing distances depend on the make and model of the lens) to achieve 1:1 magnification. But a 180mm macro lens can be as far as 50 cm away to get the same effect. This makes a huge difference while photographing skittish insects, such as tiger beetles or grasshoppers. Most insects will allow you to get as close as half a meter from them, but if you try to get any closer they will flee or start moving away.
Then there is the issue of illumination: it is much easier to achieve nice, even illumination if the distance between you and the subject is greater. For one, you are less likely to cast a shadow on your subject, and thus you may be able to use the ambient light, rather than having to use a flash.
And finally, it is easier to achieve a smooth, beautifully diffused background for your subject if your lens is longer. Compare these two photos: the first one was was taken with a Canon EF 100mm f/2.8 Macro, the second one with a Canon EF 180mm f/3.5 Macro. Both photos were taken from a similar distance, using the same aperture (f16), and in both cases the insect’s background was about 50 cm away. Can you see the difference?
The lesson here is that if your goal is to photograph a shy animal that does not like to be approached very closely (think butterflies, dragonflies, frogs); or you would like to take advantage of natural light rather than flash illumination; or you aim to isolate your subject against a smooth, blurred background, then definitely go long. My favorite long lens is Canon 180mm, but I also have had very good experience with Sigma AF 180mm f/3.5 EX HSM APO. (The latter has been discontinued and replaced with an updated model, with mounts for all major camera types.)
Both katydids shown here as examples come from South Africa. Alfred’s katydid (Alfredectes semiaeneus), named after Dr. Alfred Kaltenbach, a famous Austrian entomologist, is very common all across the Cape region. It feeds mostly on seeds, and can be found both in the mountains of the Cape, and all along the coast, even in urban areas. In contrast, the Threatened katydid (Paracilacris periclitatus) is a species that may already be threatened with extinction. I discovered it in a tiny patch of a relict Podocarpus forest in KwaZulu-Natal, entirely surrounded by pine and eucalyptus plantations.