Focus stacking deep dive

As part of my work evaluating the performance of chef's knives, I want to take close look at the factory edge. But the closer you get, the less of the edge is in focus. So, I'm using a homemade focus stacking rig in conjunction with my robot arm to capture full depth of field imagery for parts of these blades. Here's how it works.

Next, I load those images into a focus stacking program like Helicon Focus. It scans each image from the stack and only keeps the in-focus areas. The result is a single picture where everything is in focus, as sharp as my optics will allow.

The software also creates a coarse 3D model of the surface based on the focus information. This isn't a perfect representation, but it's neat.

Here are images of two different blade tips, both with factory edges. The one on the left is a Tojiro, and the one on the right is a MAC. These images don't tell the full story of performance, but they do reveal some nuances of how these blades are sharpened at the factory.

I can also look edge-on at a blade and compare the original factory edge (left) to an edge that's undergone some wear (right). Look at the very bottom of the edges in these images - that's the cutting part. The worn edge is blunted over, catching more light.

This is a case where even higher magnification would help. Time to mount my microscope objective on the camera!

Why am I doing any of this? I want to characterize the performance of chef's knives and share that information with the world. This is just one facet, and will accompany quantitative cutting performance and edge retention data, to-be-published on seattleultrasonics.com in the coming months.