Small Aperture or Focus Stacking for Macro Photography?

Macro Photography is all about photographing the little things. This can be anything from looking at microscopic organisms through specialist equipment to getting close ups of everyday objects. As you get closer to your subject, the normal “rules” of depth of field seem to change. You might be able to get a whole scene in sharp focus at f/8 when photographing a landscape. However, here is a close up shot of a watch face (focus on the end of the hand) taken at f/8:

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It is far from what we would expect if we are not used to shooting macro. No, the focus isn’t wrong. No, the lens didn’t wobble. It is simply that the depth of field gets thinner the closer you are to your subject. So, in many cases we will simply close down the aperture further to gain more depth of field. For example, here is the same shot at f/22:

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Much more is in focus than before, as we might expect. However, we still don’t have everything sharp. We are also starting to see imperfections caused by dust spots on the sense such as the one just above the watch hands in the middle. There is an additional problem that is not so easy to see at this size but if you look much closer it becomes visible:

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If we try an even smaller aperture the effect is even more pronounced. This is at f/32:

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Compare that close up from the f/22 & f/32 shots with this one from the f/8 shot:

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Although more is in focus overall, the actual point of focus (the tip of the hand) is slightly messier in the f/22 & f/32 versions. This is down to something called diffraction. At very small apertures, the light can get moved around in such ways that we can lose clarity. The smaller the aperture, the greater the chance of diffraction and the greater its impact. To make this even clearer, let’s look at a shot created using focus stacking:

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With our focus stacked image we have managed to get a much cleaner and sharper picture. If you compare the tip of the hand here with the other shots you can see that the f/32 is softest due to the diffraction. The focus stacked image was constructed from a series of shots taken at f8 with the focus shifted a small amount each time. This effectively gives us layers of sharpness that can then be stacked in Photoshop to produce one sharp image. Here is the larger overall focus stacked photo that the above crop is taken from:

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Our original image at the top of the page was shot at f/8. The focus stacked image was also shot at f/8 because it gives us sharp “slices” that overall are much sharper than using a smaller aperture. So, when you need a larger depth of field the answer isn’t always to go for a smaller aperture. The large shot at f/32 would be:

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So, going for a smaller aperture doesn’t guarantee a truly sharp image all over due to the diffraction. Sometimes, particularly if you need a very large image with all the details sharp, the best solution is focus stacking. For more on this technique read this article on focus stacking.

© Joe Lenton, Sept 2018

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