Dave, I have done some searching for you.Indeed the triplet APO lens in your case is well corrected in red & green however the blue is out a little regarding longitudinal aberration.
Here is an exaggerated plot showing how the overall focus is within 1/2mm but the blue is out.
A bit of a search found this
http://deepspaceplace.com/ed127.php
Indeed, refractors of any sought are a different beast regarding focus compared to a reflector.