Your test, showing differences or lack of differences in best focal plane for each color channel, in the center of the image ("paraxial") by doing through-focus sweeps - is testing for LoCA. No need to justify that, you're totally correct here.
If that test correctly calculates the MTF for each color channel even though it's taken from a Bayer-filtered raw source, the same test does also indicate the level of spherochromatism. That aberration (or at lest the image-relevant total average in visible light) can be reverse modeled from combining the differences in maximum MTF per channel (at the best value point) with the shape of the through-focus MTF (flat/sharp peak, and then symmetrical/rear-heavy or front-heavy through-focus curve shape).
And your through-focus test of different aperture values indicates the total level of spherical aberrations, and when you look at the shape of that curve you can also get at least a small indication of the distribution of orders of SA correction.
So - Yes, there is some point of confusion (pun intended...) in this conversation, but I don't think it's on your part. It's mainly a language / semantics barrier
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Even with a very well corrected paraxial spectrum, meaning that the lens system focuses all wavelengths of interest at the same image focal point, you can have noticeable defocus CA. I.e - no LoCA, but still OOF chromatic errors, paraxial. This is partly due to spherochromatism, as the quoted text mentions, but it also has more convoluted reasons. The pure spherochromatism links earlier in the thread are mostly explaining the aberration as it behaves in a telescope type lens, a lens that really doesn't have a central aperture. A photographic lens is typically two combined lens sets, one before and one after the restricting aperture. It is not uncommon - in fact it's more common than not - that a photographic lens has longitudinal color errors in the front group(s) (front of aperture) that are then minimized by inverting the error in the rear group(s).
The simplified explanation for defocus CA in a lens with a well corrected LoCA is in two parts - One: the pupil magnification changes between wavelengths, even though they focus at the same distance, and Two: the spherical aberrations (especially the higher order ones) differ between wavelengths.
Both effect the defocus CA, but in different ways. Chromatic exit pupil size differences can be visualized as if different wavelengths have different numerical apertures. Spherochromatism can be visualized as differing CoC intensity distributions (bright-ring, flat, central weight) between different wavelengths.
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So - if the lens has:
*No LoCA, but noticeable amounts of spherochromatic errors
----all wavelengths will share the same "best focal point" - but each inspected wavelength will have a different and unique MTF curve if you test them with monochromatic light. They will also have different defocus blur discs.
*Has LoCA, but no spherochromatism
----then each inspected wavelength will focus at a different image distance - but AT that distance, they will all have identical MTFs, both max values and MTF slopes...
Clear as mud, I suppose?
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Since both of the main reasons behind defocus CA (when isolated from "pure" LoCA) are heavily dependent on relative radii (curvature of the used lens elements compared to the overall focal length of the system), longer lenses like the 300mm's, 400mm's and so on often show much better defocus CA performance. Telefocal lenses can often use much lower maximum incidence angles per lens element than short lenses, that need to "bend" light much more aggressively. This, combined with the much more flexible opportunities to correct the higher order SA lines often give the superteles their outstanding defocus "look" performace.
Personally, I do prefer to use the term "LoCA" for both the descriptory correct aberration type AND the two other parts. Getting into spherochromatism and chromatic pupil magnification differences goes way over the head of most usage scenarios and discussions. Especially since LoCA is the absolutely dominating reason for both defocus color errors and in-focus longitudinal color error in almost all normal photographic lenses,
