Life at 8X—soybean aphid
August 27, 2012 10 Comments
Although my first attempt at adding extension tubes to my Canon MP-E 65mm macro lens, effectively converting it from a 1–5X to a 1.7–8.0X lens, was nearly a year ago, it has only been recently that I’ve actually started experimenting with this combination to obtain high-mag photographs of very small insects in the field. The first example that I showed of such a photograph was a tiny seed weevil (Althaeus sp.) on its hibiscus host plant. I’ve since photographed a number of other insect subjects at high-mag using this setup and am getting a better feel for the capabilities—and limitations—inherent in using it. First, here is what the setup actually looks like:
Not the normal photo quality for this site (just a quick field setup photographed with my I-Phone), but it shows just how long the lens component becomes when fully extended to achieve 8X magnification. The camera is quite front-heavy, making the camera difficult to use hand-held, and the very shallow DOF (depth of field) due to the extreme level of magnification makes precise focusing difficult and magnifies the effect of any motion between the camera and subject. Obviously, one solution for these problems is to mount the camera on a tripod and place the subject on a stable surface; however, for reasons I’ve mentioned elsewhere, it is unlikely that I will ever take to bringing a tripod into the field, and the whole point of this exercise is to develop the capability for getting usable hand-held field photographs no matter what level of magnification they may require. As an alternative, I use a number of other techniques, discussed in my prior post on the subject, to stabilize the camera without using a tripod.
One of the recent subjects I photographed with this setup is the soybean aphid, Aphis glycines (order Hemiptera, family Aphididae). This distinctive Asian species has recently established in the U.S. as invasive pest of soybeans; adult females measure only 1–2 mm in length (and the nymphs are even smaller) and can quickly develop very high densities on the leaves and upper stems of soybean plants. The following photograph was taken at the camera setup’s minimum magnification of 1.7X and provides a typical view of adult aphids and their progeny:
While the above photograph does a very good job of showing the colonial appearance of infestations by these aphids on soybean foliage, what about the aphids themselves? It would be nice to get a better look at individual aphids. The following photographs were all taken with the lens fully extended to achieve 8X magnification (and completely hand-held):
These photographs are not without their problems—they are a bit soft, probably due to motion blur that results from the camera being hand-held and the extremely thin DOF that makes it difficult to get all of the desired components of the photos equally in focus. Lighting also is a challenge, as the very small subject-to-lens distance forces light from the flash to come from directly above or even behind the subject while minimizing front lighting (especially evident in the last photo with its straight down view). Nevertheless, these are decent, usable photographs that provide an uncommon view of these exceedingly tiny insects—without the encumbrance of carrying a tripod in the field, the time investment of studio photography and/or focus-stacking, or the expense of a microscope-mounted camera system (for those of us without access to such systems).
Copyright © Ted C. MacRae 2012