Macro photography
What it is, and my thoughts on some ways to do it
by Andrew Hayes
Macro photography is the name given to photography of objects at reproduction ratios of 1:1 or greater (1:1 is when the subject appears the same size on your sensor as it is in real life). Anything less than 1:1 is close-up photography, anything much larger is photomicrography.
A fact known to most of you is that depth of field (area of acceptable sharpness) of a lens decreases if: a/ the aperture of the lens is increased in diameter at a given subject to camera distance, b/ the focal length increases, or c/ the subject to camera distance is reduced. In fact, any attempt to make a subject appear larger on the sensor results in a shallower depth of field, including blowing up your final image.
That is the key challenge of ‘field’ macro photography.
Another challenge is lighting – even if you have a maximum bright sunny day, you will struggle to get the best out of the situation using available light. Sure, you can increase ISO, some cameras are very good at low noise high ISO images now, but none of them maintain a full tonal range and even the small amount of noise present really takes away that crispy sharpness that you need to achieve for your image to ‘pop’.
While we are talking about light and apertures, we must talk about diffraction. Diffraction is the disruption of the light as it goes through the aperture in the lens. The photons that pass closest to the iris are moved off their ideal course as they pass closest to the iris. That means that diffraction is a problem that gets worse as you stop down the lens from wide open and the more you stop the lens down, the worse it gets. But you have to stop it down a fair bit to get your depth of field as deep as possible... Some people think diffraction is to do with lens quality – not true. Some think it is better in a macro lens than a non-macro lens – again, not true. Macro lenses are designed to work best at closer focus than non-macro lenses. Non-macro lenses are tuned to be sharper in the mid-focus range. The best thing to do is to start by adopting a hard and fast rule – don’t shoot at a smaller aperture than f16 – ever. When viewing an image you have taken at various apertures, you may (will) find that f11 is noticeably sharper than f16, but you trade off sharpness against depth of field. Diffraction changes a little with sensor size but we won’t bother with going into that here.
So, you can’t use high ISO and you can’t open that aperture to get more light on the sensor, so for the moment that just leaves shutter speed as an exposure variable. If your shutter speed is too slow or the wind is blowing the flower, or like me, you have shaky hands, then you have problems. Did I hear someone say ‘hey, my super 105mm f2.8 whizz-bang macro lens has VR (vibration reduction) or IS (image stabilization) so I’m set – right’? Not really – remember we are talking about reproduction ratios approaching 1:1? The bad news is that VR/IS is virtually useless at those reproduction ratios – there is more info on the Nikon website on this subject. VR/IS is put on macro lenses because most people rarely go larger than 1:5 and actually, macro lenses make brilliant portrait lenses and VR/IS is very useful for hand-held portraits but doesn’t help us shoot macro.
Shooting in available light is convenient and a good place to start, but has some pretty important drawbacks – there frequently isn’t enough of it, the subjects look ‘blasted’ by harsh light. Insects like sunlight because it helps them move by warming them up so they present themselves flat to the sun and the best way to minimise your depth of field requirement/problem is to shoot those wings flat-on right? Then your shadow crosses the subject and the subject sees your movement with its compound eyes then flies off to get away from what is chasing it and to find some nice sun again. A key skill in insect photography is learning the speed that insects allow you to approach at as opposed to taking flight.
The answer to most of the problems is to use flash for your macro shots,but still if you want to get the sharpest shots, there are some wrinkles to learn about using flash - here is a likely scenario: You select your lowest ISO, you turn on your flash and your camera automatically selects 1/60th of a second because you are using aperture priority (you are using aperture priority to keep control of the aperture) then you stalk your subject and take a shot but it’s still not sharp and you were sure that using flash would freeze any movement! Your most likely problem is that the amount of ambient light is enough to make a ghost image for the 1/60th of a second the shutter is open. The flash burst imprints the main image OK, but the ambient light records another blurry image on your sensor which is also visible and which detracts from the sharpness of the final image.
You can change your camera to manual exposure mode and increase your sync speed to 1/200th or even 1/250th of a second. That will do the job of a clean exposure in most cases, but the method I use a lot is to set the camera in manual mode to considerably under expose the ambient light and top up with a heavier burst of flash.One set-up and forget the camera – just concentrate on finding and stalking your subject. All but the oldest or most entry level DSLR’s can do it if you use a compatible flash: It is called high speed synch (HSS) and using this, the camera and flash will get your exposure right down to 1/4000th or 1/8000th of a second. Instead of emitting a single ultra-fast pulse of light, which would give you a correctly exposed ‘bar’ in the middle of the image with black areas to one or both sides of it, the flash emits a string of pulses very close together in time so that they appear to the sensor to be one long pulse and they continue for long enough to illuminate the whole sensor while the shutter curtain travels across it.
We aren’t there yet. We have selected our deepest sharp depth of field (aperture) but we still need to realise that at 1:1 the depth of field is about a third of a flies head at f11! How are we going to get the right part of the image pin sharp with such a shallow depth of field? There are a few ways; the one I use most often is continuous servo focus mode. I put the selected focus point on the part of the subject I want sharp then the camera takes care of focussing while I am shaking and swaying around. This will not – unfortunately – result in 100% in-focus shots, I still have to be super careful about stance and breathing to stand even a 1 in 20 chance of a sharp picture and 1 in 10 is a result for pictures with the right area in focus – but it is a start. Another way is manual focus. If you know what size you want to see the subject in the viewfinder, pre-set the focus and use the sway focus technique – but you have to be careful how you release the shutter button – the instant you are in focus, but not with a big ‘stab’.
A few words on flash: Some of the very best macro shots I have seen are taken using basic flash guns and improvised light modifiers. You can get good results using a ready-made £5 ebay Chinese fold-up modifier – you don’t need to carry a studio or spend a fortune. The small flash light modifiers, when arranged close to the front of the lens for photographing small insects are like 20 foot by 20 foot light modifier are in comparison to a person – lovely wraparound ‘soft’ light. You may need to buy a flexible bracket and a cheap sync lead to get your flash head where you need it, but assuming you have a camera, lens and flash already, an excellent macro set-up will only cost you £30 off ebay (sync lead, bracket and light modifier).
There is another approach to getting round the problem of shallow depth of field; it is called focus-stacking. Focus-stacking is a process where you arrange your camera on a tripod and either manually focus your lens at say, 1mm intervals covering the area of the subject you want to be sharp, or you use a small rack and pinion to move the entire camera and lens at the same fine intervals. This method gives fewer aberrations from frame-to-frame than just guessing the focussing of the lens because it is more consistent as it is easier to control the increments that the focus plane is adjusted by. The frames are all combined in a free program called Helicon Focus or Zerene Stacker and the results can be spectacular, although to my eye sometimes they look ‘wrong’ – like a computer generated image - I expect to see a depth of field and out of focus areas – but that is just my personal opinion or perhaps the difference between our field macro photography and illustrations in a biology text book.