Spherochromatism

Can someone please tell me whether I have this correct:

At best focus for white light, any refractor other than a full apo will have significant spherical aberration in one or more colors since you are effectively defocusing some wavelengths (the wavelengths that are not brought to the same focus as green). So even if a semi-apo has SA well controlled when focused for individual colors, there will still be spherochromatism present at best focus for white light.

You are referring to Chromatic Aberration where different wavelengths/colors focus on a different plane in less well corrected achromats compared to apos..
You will have some amount of SA in very fast apos, this shows clearly in defocused star images on both sides of best focus, one big advantage of long focus apos is near elimination of SA from the system.

Vahe