This is an excellent point, but could you expand on that "all else"? I've been happy for years with 32mm Leicas in which CA can be evident around the edges of the field, and probably detectable (if not by me) even at the center. Yet the view stil seems excellent, in that "microcontrasty" way people describe...
Lack of CA doesn't make a bin good optically, or good for birding. It can fail in many other ways.
A bin w/CA that does many things very well can still have superb optics and be enjoyable to use. I've enjoyed and gotten excellent use out of many bins with a lot of CA, including the Leica 8x32 BA Ultra Trinovid and 8x42 Ultravid, and the Swarovski 8x32 EL (pre SV).
I can see CA when I want to, and (if it is moderate) can tune it out when I want to. I'm very happy to use some otherwise excellent bins that suffer from CA. Nevertheless, I don't pretend that CA isn't a detriment to optical quality, and to the extent it is possible to design bins with less CA, I'd like to see it done. Unlike many birders (it seems, based on experiences in group situations in the field), I am willing to take the trouble to observe very distant birds, at the limits of my vision, and I find that I am able to identify them accurately quite often. In those situations, I find a bin with low CA may deliver, when a bin with more CA cannot, even if CA isn't impinging on my awareness. That is one reason that my Zeiss 8x32 FL replaced my Leica 8x32 BA Ultra Trinovid as a travel bin.
...What is the difference, as meant here, between "corrected away by the brain" and "hidden from awareness"...
My apologies to experts for likely not using proper terminology, but what I mean is as follows. Anything that your eyes/brain do to remove optical flaws or receptor noise from perception is an example of hiding aspects of sensation from awareness. For example, each of our eyes has a blind spot to the side of our central vision, but generally our brain hides it from awareness, so we don't "see" it. With both eyes open, the brain can perhaps use the information from the other eye to fill in what is missing from each eye. With only one eye open, the brain can only speculate on what is missing based on surroundings and so fills in the missing bit with imagination of a sort. There is no way to correct away the missing sensory data, only hide it from awareness by making up substitute data in constructing what we perceive. However, something like distortion (e.g. pincushion) can be removed from awareness by being corrected away by the brain so as to recover an accurate-about-the-world perception. The sensory data can be re-mapped by the brain so that perception is such that the distortion has been removed. In this case, no data is missing. The re-mapped subjective mind's eye vision is complete and, in a certain sense, a more accurate rendering of the world than is the distorted projection from the optical system. I can't deny that my Swarovski 8.5x42 EL SV has a lot of AMD, but when I look through it in normal use, I see no rolling ball.
--AP