Focus Stacking – What magnification ratios do I need?

Microscope objectives enable extremely high magnification ratios when using the focus stacking technique. But which of these magnifications are truly practical for specific cases? After all, high-quality objectives can be quite expensive, mostly increasing in price with greater magnification. Additionally, working with higher magnifications becomes significantly more challenging.

The focus stacking technique has developed over the past two decades and has gained popularity among macro and micro photographers worldwide. Today, it allows us to capture delicate details in animals, plants, electronic components, and many other subjects with far greater precision and sharpness than was previously possible. This advancement is so significant that it essentially bridges the gap between macro photography and electron microscopy.

Some beginners develop ambitious goals, wanting to capture ever more detailed structures on insect bodies and push the boundaries of what's possible. While there's nothing inherently wrong with that, it’s important to note that even moderate magnifications with a microscope objective can render your subject extremely detailed. For example, if you compare an image of a fly taken with a microscope objective like the Mitutoyo M Plan Apo 5x or HLB Plan Apo 5x to a photo of the same fly taken with a conventional camera lens at the same magnification—such as the Canon MPE 65 macro lens at 5:1—the resolution advantage of the microscope objective is immense. However, you can only truly appreciate this difference when you scale up the image and view it in larger detail. Nevertheless, the depth of field with a microscope objective is so much shallower that without focus stacking, you won't achieve a usable image.

Less is more

A moderate magnification ratio of 5x offers many advantages over higher ratios like 20x or even 50x. One advantage is that you can capture a larger portion of an insect's body or even the entire insect. A tiny detail separately captured with high magnification doesn't show the whole object. For instance, if you only have an image of an insect’s foot at an extremely high magnification with precise detail, the context of the entire insect is lost. Only with this context can you truly appreciate the scale of the magnification, and this is what makes such detailed images impactful. Lower magnification ratios reveal much more, often showing a large part of the insect's body or even the entire insect, which is often more appealing to many viewers than a tiny section with nearly electron-microscopic precision.

Another benefit of smaller magnification ratios, particularly for beginners, is the reduced tendency for artifacts. Artifacts are imaging errors that disrupt the photo in some way and create an unintended difference from the subject being photographed. These can include blurry, fog-like fringes around a contour or oddly shaped spots that frequently appear throughout the image. Sometimes, a structure that should be behind another appears in front in the final image, and it's transparent (I plan to discuss the topic of artifacts in more detail in a separate article). The likelihood of artifacts increases significantly with higher magnification ratios, and if you’re not expecting them, they can quickly spoil your enjoyment of this wonderful photography hobby. This is especially frustrating if you’ve spent a lot of money on a highly magnifying microscope objective as a beginner.

Start with lower magnification ratios

Therefore, as a beginner, you should start with lower magnification ratios and gain your first experiences there. A 5x ratio is an excellent starting point, and 10x is a good next step. Working through a variety of subjects at these magnifications can yield a surprisingly steep learning curve, and after a year, you’ll have gained a lot of experience.

Before purchasing expensive, high-magnification optics, you should be fully aware of the difficulties you’ll face as magnification increases, as you’ll pay a high price not just in monetary terms. The work with microscope objectives generally becomes more challenging as magnification increases. This not only applies to the mentioned imaging errors, the artifacts, but also to the decreasing depth of field. This means you’ll need more individual images, which in turn increases the risk of artifacts.

Any shortcomings in your focus stacking setup or working procedure will also become more apparent as the magnification increases. I remember a workshop visitor who had difficulties with a certain high magnification microscope objective because the focus stacking images he produced with that always were kind of blurry and out of focus. At lower magnifications, on the other hand, he had no focus problems. This led to the assumption that both the technical focus stacking setup and the working procedure must be in order. Only the objective could be at fault, e.g. due to a single lens that had shifted slightly as a result of a bump, which could of course cost sharpness. However, it turned out that the problem was very different: he had his computer on the same table as the focus stacking setup. The vibrations created by the Windows computer - presumably from the cooling fans - did not yet lead to visible changes in the image at lower magnification scales. With higher magnification lenses, however, this resulted in significant blurring that could not be influenced by any other measures. Only moving the computer to the floor solved this problem quite abruptly. This shows how intolerant microscope objectives with high magnification scales usually are.

Also, any mechanical tolerances in your focus stacking setup that go unnoticed at lower magnifications can become ruthlessly apparent at higher magnifications and ruin your images because the laws of physics are unforgiving.

Another consideration is lighting. The light requirements of a 50x objective are enormous, and if you’re working with LED lamps, you may need a camera capable of producing noise-free images even at very high ISO settings. 50x is essentially the „royal class" where you have to pull out all the stops. Each good microphoto you take requires significantly more setup time, technical equipment, and experience. My HLB Plan Apo 50x is a diva that demands perfection in every aspect, while its smaller 20x sibling is also demanding but noticeably more forgiving. In comparison, good photos can be taken with the 5x and 10x objectives almost effortlessly—ideal conditions for starting without frustration.