Jay P Morgan from the Slanted Lens is showing you how to calibrate a lens.
Instead of the Focus Pyramid mentioned in the previous article, he’s using Datacolor’s SpyderLENSCAL. But it really doesn’t matter what brand you’re using, you can even find instructions online to make a calibration tool yourself.
Since I shoot a lot of older manual focus lenses (my niche is macro) this isn’t needed
This happens a lot to zoom lenses rarely to prime lenses. that is why I stopped using zoom lenses unless it’s absolutely necessary.