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Focus Stacking or Small Aperture for detailed Insect photos?

I'm sure a lot of wildlife photographers will disagree with this article but all I can say is that what's in here works for me.


I spend a lot of my photography hours doing macro shots of insects like butterflies, crickets, flies, bees etc. Depending on the location and the available light, I end up using quite a wide range of exposures and equipment to get the perfect shot. My favourite technique for getting the most detailed image is Focus Stacking. This involves taking many focus 'slices', covering the whole insect, which are then merged together in software to produce a highly focussed image. The problem with this technique is that it is very difficult to use in the field. The ability to take 50+ shots of an object and then merge them all together depends on the object remaining perfectly still. The slightest movement creates an unacceptable blur on the image and ruins it. It is possible to limit this in the software but it doesn't always result in a good image. In general, all my focus stacked images are insects that I have found dead but, occasionally, something will sit still long enough for a good result in the wild. Bush-crickets, spiders, mantids and some flies will frequently pose long enough for a decent collection of images that require minimal adjustments.


Once you have created a few of these focus stacked images, you realise just how limiting the depth of focus (DoF) is when using aperture adjustment in normal photography. In normal lighting conditions, an aperture of f/8 - f/16 is generally possible with an ISO around 200 (less than f/8 isn't worth using unless you're photographing something like an open wing butterfly from above) but the DoF is limited and great care has to be taken when focussing. With butterflies, I have to be content most of the time with some soft areas on the image under field conditions.


Illuminating the subject with a flash (I use a cheap ring flash) opens up another range of opportunity, you have the ability to use much smaller apertures above f/16 and a lower ISO in order to get more of the subject in focus. Conventional wisdom says that working with very small apertures results in increasingly poor image sharpness as the aperture reduces. In the field, I generally use the ring flash and an aperture of f/22 which gives me acceptably sharp, well-focussed images. My camera and macro lens combination (Nikon D850 and Nikon 105mm Micro 1:2.8 lens with 36mm extension tube) allow me to go to f/57, but I've never bothered to go that small because of the sharpness issue. I have heard several times that some macro photographers don't bother with the fuss of Focus Stacking and use smaller apertures instead, so I decided to have a look at exactly what the situation is.


While sorting out the wood pile I found a bush-cricket that was in good condition but had died some time before. A good test for a comparison of Focus Stacking over Small Apertures.


After cleaning it with an air brush, I set up the bush-cricket in my studio (spare bedroom!) and mounted the camera/lens/ring flash (TTL) on a tripod for the photo session. I set the camera to f/11, 1/250s, ISO 64 and set the focus on the foot of the leg nearest to the camera (circled in red). I took a stack of 50 photos at a narrow focus width to get the whole insect in focus without going too far beyond it. I then reset the focus point and began taking individual photos at f/8, f/11, f/16, f/22, f/40 and f/57 for the comparison. The results are as follows:

f/8, 1/250s, ISO 64 (focus point circled in red)

F/11, 1/250s, ISO 64 - Same focus point

f/16, 1/250s, ISO 64 - Same focus point

f/22, 1/250s, ISO 64 - Same focus point

f/40, 1/250s, ISO 64 - Same focus point

f/57, 1/250s, ISO 64 - Same focus point

Focus Stacked image (50 shots at f/11, 1/250s, ISO 64)


The results are very surprising!

While the DoF in the larger apertures is as you would expect, the clarity and DoF at f/40 and f/57 are surprisingly good. It should be noted that because the focus point was constant for all of the photos, the focus shift image had an unfair advantage in that the focus point moved for each of the 50 exposures. If I had moved the focus point to the centre of the DoF at each of the individual apertures, the results might have been even better.


Without a doubt, the image shot at f/57 is incredibly good considering the negative reports of using such small apertures, and the ring flash did a good job of illuminating the subject. When compared to the focus stacked image however, the f/57 image is nowhere near as sharp at any point. Shifting the focus point on to the body might have improved the overall image but it still wouldn't be able to compete with the focus stack.


CONCLUSION:

For me, Focus Stacking remains by far the best option to create very highly detailed images with the caveat that the subject and location need to be carefully controlled in order to benefit from the technique.


The results at very small apertures are excellent provided there is a suitably bright light source to enable a correct exposure of the subject. As a rule of thumb, use up to f/16 in daylight and up to your minimum aperture with artificial light such as a flash or ring light.


A note on ISO:

All these shots were taken using a TTL Ring Flash set at -1/3Ev which allowed me to use ISO 64 for all images. I rarely go above ISO 250 for macro shots and this will limit how small an aperture you can use in daylight conditions.


I'm off to order a better ring flash!!!



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