Yesterday I wandered into the realm of photographing insects. This is something I am not totally new to, having dabbled a bit with damselflies and butterflies in the good old days of film, but it’s at least 20 years since I dabbled and even then I was no expert. However, because of my previous experience, I was already aware of the theory and practice of “macro” photography, which I learned at the time. “Macro” really means subjects that are life size or greater at the film/sensor plane, but the term is often loosely used to refer to close up photography of small subjects and I will use it in this article in the latter context. In most case my subjects were approximately 1/3 to 1/2 life size at the sensor plane.
Twenty years ago, I had a manual camera, film and a 90 mm manual Tamron macro lens. I had a purpose made boomerang style bracket and two small flash guns with an optical trigger. It was a slow and cumbersome system and, of course, these days, our equipment is very different.
Nowadays, I don’t possess a long macro lens that is optimised for digital sensors. My old 90 mm Tamron still works manually on my modern Pentax camera, but there is a low contrast area produced right in the centre of the lens (just where you want maximum quality). We discovered this during some MTF (modular transfer function) testing of the lens a couple of years ago and think it is probably caused by some internal reflections. Since then I have been looking for a third party long focus macro lens, 150mm or 180mm would be great, but they are either not produced at all or are as easy to find as rocking horse droppings.
My digital SLR camera is, of course, fully automatic and I do have a modern 35mm macro lens, but working distances are too close to be comfortable with insects. My bent bracket and small flashguns are lost in the mists of time. The only thing I still have is a modicum of patience and plenty of memory cards plus a 3 Dioptre screw-on attachment, which is really my Dad’s but is on loan. This is a Marumi 72mm DHG Achromat Macro Lens 330 (+3). The 72mm filter size is priced at the time of writing, at £74 at Wex Photographic. It’s hard to find any reviews of this attachment on the web, but I had seen the results from a fellow club-photographer, which were very impressive.
Depth of field (DOF)
Depth of field is a major problem with macro work.
For a given sensor size, there are just two things that determine the depth of field…
The magnification of the subject at the sensor plane and the aperture chosen.
I find it impossible to work out DOF “on the fly” but it is easy to quickly get a feel for just how small the Depth of Field is in practice. There is a brilliant section on macro photography at Cambridge in Colour and I would strongly recommend a browse through their article and have a play with the DOF calculator. You will soon discover that, for example, on an APS C sensor, with a 1.5 crop factor and subject at half life size at the sensor plane and an aperture of f/8, DOF is only about 2 mm. Changing to f/16 only doubles the DOF to about 4 mm. That’s not enough to get a whole bee in full sharpness. Something has to give.
Cambridge in Colour also has a calculator so that you can work out the aperture at which a lens becomes diffraction limited. This is an optical effect which causes the image to become less sharp due to the dispersal of light as it passes through the pupil of the lens and this softening increases at the aperture gets smaller. This effect is also explained here at Cambridge in Colour.
The problem is that, although Depth of Field increases as you stop down, so does diffraction, so what you gain in depth of field, you lose in overall sharpness. Only with practice can the photographer decide what is the best compromise. Do you pull back so the subject is smaller in the frame, stop down more or less?
For the photos in this post, I used a Pentax K5 IIs with a 50-135 DA* lens plus the Marumi Achromatic +3 attachment. For some of the photos, I used the camera’s pop-up flash, set to give a -1 stop compensation, for others daylight was sufficient.
The close-up attachment severely reduces the range within which focus can be achieved and I found this to be a bit troublesome at first. I found that the insects had flown before I got them into focus. However, with practice, again I got a feel for the distance and, as time went on, I became better at judging.
I soon learned to stop shooting anything and everything and try to concentrate on getting better, simpler, backgrounds…easier said than done…but at least I know what I am looking for. The bokeh produced by the combination of the Pentax lens and the Marumi attachment is quite pleasant and the best effect is produced when the background objects are far enough away to be out of focus.
The hardest thing is getting the camera into the same plane as the insect to maximise sharpness. This sounds easy, but the insects do not stay still! In full sun and in the middle of the day, there are plenty of insects around but they are very active. Early and late in the day they are likely to be a little easier to track down. Focusing about 1/3 into the insect helps to take best advantage of what DOF there is.
At present, the darn critters only like the hebe in my garden, so most of the shots I took are on the same food-plant. Hopefully, when other plants become “ripe”, I can find some new backgrounds. Fortunately, purple is my favourite colour and it serves well enough to practice! So now the woman who hates wasps has her head in a bush full of ’em…what we do for our art!
Some more examples: