Archive | July 13, 2012

The mantis wasp

Mantis wasps (Torymidae: Podagrion) are tiny, parasitoid wasps that develop in preying mantis’ egg masses, or oothecae. Each developing wasp larva consumes a single egg in the ootheca (which can contain several hundred eggs), but in some areas the number of these insects can be so high that it is a miracle that any mantids survive at all. Podagrion wasps can be  identified by the combination of a very long ovipositor and huge hind legs, which are used by the female to guide the ovipositor directly into the mantis eggs (I have always been impressed by the similarity of these legs to the raptorial legs of a preying mantis, the wasps’ host.) I photographed this wasp, which was only about 2 mm long, in Cambodia as it emerged from an ootheca of a preying mantis; surprisingly, this female was the only individual to emerge, which was good news from the remainder of the eggs.

Mantis wasp (Podagrion sp.) freshly emerged from a preying mantis’ ootheca [Canon 1Ds MKII, Canon 100mm macro, Canon MT-24EX twin light + Canon 50EX speedlight]

Female mantis wasp (Podagrion sp.) cleaning her ovipositor [Canon 1D MKII, Canon MP-E 65mm macro, Canon MT-24EX twin light + Canon 50EX speedlight]

 

Macro lenses: shorter is better (often)

What is the best lens for macrophotography? In an earlier post I argued that long lenses, 100mm and more, are great for photographing small subjects that are easy to scare off, and need to be photographed from a distance. They are also handy if you want to isolate your subject from its background. But what if the goal of your photography is to showcase not only the organism itself, but also its surroundings or relationships to other animals and plants? What you need in that case is a short lens.

The two very important things that are worth knowing about lenses are that (a) their focal length determines their angle of view, and (b) their focal length is correlated with the depth of field you will be able to achieve with the lens. The general rule is that the shorter the lens the wider its field of coverage. For example, a 180mm macro lens has the angle of view of only 13°, whereas a 60mm macro lens, being 3 times shorter, will have the angle of view of 39° – three times as much. In practical terms this means that if you fill the frame with an insect, the shorter, 60mm lens will also allow you to show three times as much of the insect’s background as the long, 180mm one.

Red-eyed tree frog (Agalychnis callidryas) from Costa Rica [Nikon D1, Sigma 180mm f/3.5 APO, ambient light]

Shorter lenses are also better for achieving a greater depth of field (DOF) than longer lenses at the same aperture. DOF is more difficult to quantify than the angle of view, but a difference of just a few millimeters in the lens’ focal length can make objects that are meters away from the center of focus appear much sharper. Sometimes this can be undesirable, for example if the background is busy with ungainly twigs and branches that distract from the main subject. In such a case a longer lens is better. But if you do want to show as much of the subject’s background as possible then the shorter the lens the sharper the background will appear.

The tradeoff in using short macro lenses is the working distance, or the distance between the lens and the subject that is needed to achieve maximum magnification, which gets shorter with every millimeter subtracted from the lens’ focal length. Again, a 180mm lens will allow you to achieve its maximum magnification from a distance of about 50 cm, whereas if you use a 60mm lens then you will need to be as close as 17 cm from the subject – about one third of the distance. But as you gain practice with microphotography you will quickly discover that even the most agile, skittish insects and other small animals can be approached very closely if you show enough patience.

Red-eyed tree frog (Agalychnis callidryas) from Costa Rica [Nikon D1X, Nikkor 17-35mm f/2.8 IF-ED, fill-in flash Nikon SB-28DX]

The difference in the effect of long versus short lenses can be seen in these two photos. The first one was taken with a 180mm lens (Sigma 180mm f/3.5 APO). This lens allowed me to get a very tight portrait of the iconic Red-eyed tree frog, while the background remains unobtrusively diffused. But this image lacks context, and it could have been taken in a studio (although it was taken in the Costa Rican rainforest.) For the second photo I used a very short lens (Nikkor 17-35mm f/2.8D IF-ED; technically not a macro lens, but one that focuses close enough to be used for small natural history subjects.) Here the background of the animal is prominently displayed, making for a much more interesting, engaging portrait. There is no doubt that this photo was taken in the animal’s natural habitat, and it conveys more information about the frog’s life.