Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Digital macro-photography of aphids
|Macro photography is extreme close-up photography. (In the past the term was sometimes used to refer to taking very large photos!).|
For digital single lens reflex (DSLR) ultra-macro photography: Use flash. Minimize aperture. Minimize ISO. Set everything to manual. Save to hi-res jpg. And learn to take control.
If none of that makes sense to you, read on...
|A micrograph is a photograph taken using a microscope. (Beware: Canon describe some of their macro-lenses as micro-lenses).|
|A T-mount is effectively a light-excluding tube, with non-reflective inner surfaces, which enables a camera to be fixed to a lens-assembly such as a microscope.|
Photography showing details of very small insects started with micrographs of insects permanently mounted on glass microscope slides. The technology for these has changed little since the mid-1900s. You require a microscope with good quality lenses, suitable illumination, a camera, a T-mount - and an appropriately long exposure time...
Such images, given the optics of light-microscopes, have little or no depth of focus - so are usually of suitably prepared, immobile very-flat dead specimens, sometimes clarified and stained to reveal key features.
From the 1930s onwards, electron microscopes (which use electrons instead of light) enabled scientists to produce exquisitely detailed high-contrast high-magnification micrographs. Transmission electron microscopes (TEMs) give little or no depth of focus, but scanning electron microscopes (SEMs) can give a high depth. All EM micrographs are in greyscale (black and white) unless their images are artificially colorized.
Image public domain, by Louisa Howard, Rippel Electron Microscope Facility, Dartmouth College, UK.
Electron microscopes are not suitable for an individual field worker to carry around in their backpack. Nor are they cheap. They range from £95000 for a (new) transmission microscope to perhaps £700000 for a (new) scanning electron microscope. Also, until quite recently, electron microscopy tended to cook biological material.
|Digital cameras record images onto re-usable memory, rather than expensive single use film - and include all manner of clever software to automate your photography.|
Until recently live aphids required very specialized equipment and personnel to photograph. This was usually done under controlled conditions - aphids being very small 3-dimensional objects, and liable to move. The same points apply to specimens in liquid preservative (known as wet-preparations), except they do not move - at least not under their own volition.
Macrophotography of live aphids under field conditions, using photographic film, was even more difficult - but, if you wanted usable close-ups, they tended to be frighteningly expensive and time-consuming. In addition, colour photos generally require more light than black and white ones.
The advent of digital photography, especially digital single lens reflex (DSLR) cameras, has improved matters considerably for macrophotography of live aphids - but several issues remain.
Modern sensors have more pixels per inch, but lots of pixels don't compensate for poor lenses.
|Full frame sensor cameras have a physically large image sensor (hence more pixels) - so are bulky. Most DSLRs are crop sensor.|
Whilst DSLR results can be very good, they require a suitably deep pocket, and a certain amount of photographic and biological knowledge.
|Bridge cameras fill a niche between the single-lens reflex cameras (SLRs) and the point-and-shoot camera. They usually have an electronic screen rather than an optical viewfinder, and are of similar size and weight to the smallest DSLR.|
Recent bridge cameras can also yield good macro-photographs but, whilst sophisticated and user-friendly, they are not suitable for ultra-macro work.
Aside from the virtual disappearance of professional photographers, for aphid photography the advent of mass-produced digital cameras has produced two very different outcomes:
Photographed at F/64, at 1/200 second, ISO 200, using flash, manual exposure and auto white balance.
Image by InfluentialPoints, Copyright CC BY 3.0
Since ultra-macro-photography is a rather specialized field, whilst we expect the technology will continue to improve, it is possible to greatly improve image quality with that sort of currently-available and modestly priced equipment - given a little knowledge.
With old-fashioned paper photographs there was no confusion regarding image size, quality, and resolution. With digital images people often confuse image size in inches (or cm) with image size in pixels (or dots) with image size in bytes (or kilobytes or megabytes) with its file size following image "compression".
These partly arise because, with modern technology, "anyone can take a photograph" - and, for everyday purposes, it can work pretty well. For non-everyday work, it helps to know what you are doing. Note that having the camera sharpen the image prior to saving merely introduces additional artefacts! Many images get sharpened several times over: first by the camera's auto sharpen, then by image auto-editing, then by sharpening-during reduction...
Solving those issues need not be especially expensive - provided you ignore much of the conventional wisdom for macrophotography.
Most photographer's idea of macrophotography is a close-up of someone's face. Wildlife photographers view it as photographing an insect which is between 10 and 50mm across. But aphids (and many other groups of insects) are much smaller - in some species the adults are less than 1mm long, and the details you need to be able to see for identification (such as antennal hairs) are very small - from 0.1 to 0.01 of a millimeter, or less. To see what is needed to identify an aphid, the insect should fill about 50-70% of the picture and be sharply in focus.
|Macro lenses offer at least 1:1 magnification - and, as opposed to telephoto lenses, are specifically for photographing small, close, objects.|
Our own preference for focal length is 90mm, as this means the distance between the object and the lens is not so small as to render good lighting difficult. If you have a Canon camera, you have the option of their new 5x macro lens which (for a price) gives you (nearly) all the the magnification you need in one go.
|An extension tube is a light-excluding tube between the lens and camera body, which increases magnification, but reduces lighting and depth of focus. Modern DSLRs require "auto-extension tubes", so your camera and lens can communicate.|
|A teleconverter is a magnifying lens assembly between the camera body and the existing lens. It slightly reduces lighting, and may introduce aberrations.|
Whichever you use, ensure it has electrical contacts so that you can control the aperture of the attached lens (most DSLR cameras require this).
Extension tubes can be less expensive, and are theoretically better because they do not introduce distortion, but a good teleconverter is easier to use (unless you have arms like a gorilla and cordination a gymnast would envy).
|A xenon-flash produces a very brief high-intensity flash - but is expensive on batteries.|
|An LED flash produces a comparitively-long low-intensity flash - but is cheap on batteries.|
|A ring-flash has a circular light-producing element, fitted with a light-diffuser, and mounted around the far-end of the camera lens.|
|Camera flash diffusers scatter light, making its source effectively larger, which reduces shadows - but also the flash intensity. If all else fails a hankerchief is sometimes used.|
|The auto-settings of a digital camera do the thinking for you - so are OK for the novice, given a set of common requirements. Aphid macrophotography is not a common requirement.|
|Digital camera ISO is akin to ASA of film. A low ISO yields sharp images, given enough light. A high ISO-setting needs less light, but gives less sharp, more grainy, images.|
With a bit of trial-and error you can produce far better results without them.
|jpeg (=jpg) is a "lossy" image-compression format. A high-quality jpeg compression looses little information, and introduces few artefacts, but takes more space (=kbytes, or Mbytes) to store.
Low-quality jpeg images require less storage space, but have low resolution - and introduce, largely unremovable, jpeg artefacts.
Low-quality, highly-compressed jpeg files are generally a waste of time when photographing aphids.
Uncompressed, "raw", TIFF, or other lossless-format files may be better in theory, but require frightening amounts of storage.
Note: the image sizes quoted by image-selling websites are the image size (in MB) of a bitmap-file of equivalent size. For example if a camera has a 10 Megapixel (MP) sensor, at the conventional colour depth of 8 bits per pixel bitmap-format, each image would require about 30 Megabytes (MB) of storage.
Since we are sometimes contradicting conventional wisdom, a few words of explanation are in order.
Using several extension tubes or teleconverters increases the magnification, enabling you to photograph smaller objects. But - using these reduces the amount of light reaching the camera, and reaching your eye when trying to focus - they also mess up many of your digital camera's built-in auto features, including its response-time once you press the shutter release.
|F-stop is a measure of iris aperture. F/4 is a wide aperture, F/32 is a narrow aperture. A wide aperture permits more light to reach the camera image sensor, allowing shorter exposures, at a lower ISO. Narrow apertures give more depth of focus.
Macro-photographers commonly advise using a large aperture to blur the background, and to use sunlight. That is very bad advice for aphid photography, given the issues described above.
Flash also enables you to minimize the ISO (giving the least grainy image), and obtain a directional light source (which, unlike a ring-flash, gives some shadows and hence a less "flat-looking" image). Flash also compensates for including teleconverters or extension tubes - and allows you to minimize the aperture (ideally to F/32 or F/64) and obtain the best depth of focus.
Diffusers can be used to "fill-in" unwanted shadows, but too much diffusion removes too much shadow - and reduces the light reaching your subject.
Aphids that feed on the trunk of a tree, such as the giant willow aphid, are a good example - taking part of a tree trunk back to the studio is a little problematic, even assuming the aphids stay in place. Photographing interactions with ants can often only be done in the field - especially with wood ants, which seldom behave naturally in the studio.
Image copyright Alan Watson Featherstone all rights reserved.
"The twin lite flash unit is especially designed for macro photography, and provides good flexibility in terms of positioning the flash units to give optimal lighting.
All auto camera settings are disabled or set to manual, including exposure. To minimize ambient lighting, shutter speed is set at 1/200 of a second and, to get maximum depth of field, aperture is set at the smallest possible for each lens. For the 100 mm lens this is f32, and for the 65 mm lens this is f16. The under/over exposure function on the flash unit is varied to get the correct exposure.
With the 65 mm lens, especially at its maximum 5 times life size magnification, the depth of field is extremely limited and the image is quite dark when seen through the viewfinder, because of the long extension to the lens at this magnification, and the small diameter of the lens' front element. It is quite a challenging lens to use, and at 5 times life size it can be very difficult even to find the subject when looking through the viewfinder.
Almost all of my aphid photography is done with the camera handheld, but occasionally I'll use the 100 mm macro lens with the camera on a tripod, particularly if I want to shoot some video footage, in addition to taking still photos. - I've developed a technique of holding the subject in the fingers of my left hand, with the front of the barrel of the lens resting on my left hand, and I can then use the position of my hand as both a guide to find the subject through the viewfinder and to minimise the movement of the subject relative to the camera, so that it stays in the plane of focus.
With the 65 mm lens I will often take several photos in quick succession (determined by the flash recharging time) to make sure that I get an image where the subject is in the plane of focus."
Image by InfluentialPoints, Copyright CC BY 3.0
Compared to its contemporaries, this excellent crop sensor DSLR has an unusually large sensor (ie. lots of pixels). The Tamron lens is also regarded as one of the best in its price range. Jessops teleconvertors are surprisingly good and reasonably priced at £40-80 (used) - they are sadly no longer manufactured, so look on e-bay. Kenco DG N/AF auto-extension tubes are £90-120 (new) but we prefer the teleconverters: partly because, in order to obtain an equivalent magnification using extension tubes, the assembly becomes over-long - and strains the couplings.
The Nikon close-up flash is specially produced for close-up photographic exposures, and is the least satisfactory component of the gear - it is overpriced and poorly engineered. The combined kit is too unwieldy, vulnerable and clumsy-to-use for field photographs - but can give remarkably good photos under studio conditions, albeit the flash kit is somewhat battery-hungry. This combination also has an annoying, unexplained, 1 second wait before each shot - even when everything is set to manual.
We take most aphid photos using two x2 teleconverters which means that (with experience) it is still fairly easy to find the subject in the viewfinder. This will produce a full frame picture for alatae of the larger species, and for a group of two to three apterous aphids (wingless adults). Adding a further teleconverter to give 8x will produce a full frame picture of an aptera, but finding the subject is difficult and depth of field is restrictive.
For maximum flexibility we grip a piece of plant hosting the aphids in a hobbyist's clamp, and steady the camera on a bean bag. We occasionally hand-hold, but never tripod-mount this camera - aside from its weight and unwieldyness, a tripod-mount puts too much strain on the lens couplings and camera body. To avoid unwanted heat, we use an LED anglepoise or LED desklamp to illuminate the sample when focussing.
Image by InfluentialPoints, Copyright CC BY 3.0
This camera body and lens are the slightly older counterparts of those above - with similar advantages (and no 1-second wait). When mounted in the camera's hotshoe, the flash only provided enough light for shots at ISO 400. Mounting the flash on the telephoto lens with a lead to the hot shoe greatly improved performance. This kit is good for field shots.
Prior to this camera's internal flash dying from overuse, we used an internally-reflective extension tube to concentrate the flash close to the subject. This inexpensive home-made device was made of plastic, and hence lightweight, rugged, did not need extra batteries and generally allowed us to shoot at ISO 100. It was as long as the lens, lined with aluminized mylar, held together with sticky tape, attached to the camera with elastic and velcro - and covered in "Fragile" tape (in case it was knocked off).
Image by InfluentialPoints, Copyright CC BY 3.0
If you want to see what sort of kit others are using, flikr have a page called Show us your Macro gear .
Our thanks to the numerous people who contributed ideas, information, and the varied questions which prompted us to write this page. We especially thank Ian Dawson, whose comments about aphid photography and photographic equipment provoked much useful thought.