adhoc, is it possible that seeing CA is made more likely by some forms of loss of acuity? I don't know - it's just a thought.....
I'm 55 and have very good acuity AFAIK. At least opticians always talk about the fact that I have very good 'correctability' by which they mean that I have almost 20/20 vision which the right prescription. I'm am very slightly short sighted (-1.00) and have a slight astigmatism in both eyes, but otherwise no problems. I have my eyes checked regularly because there is a history of glaucoma in my family.
I can certainly induce CA in my 7x42 UVHD+ but I never see it in normal use. I've always thought that CA was largely a function of poor IPD and focus, but I'm no expert and defer to those who are. However, my only bin for years and years was a 10x25 BCA and I think that because of my experience of using that bin I am good at setting the IPD correctly. After all, if you don't set it right with a bin with an exit pupil of 2.5, you know about it pretty soon!
Mike, Sorry about the very long delay in responding! I was away much that weekend and a few days after. Then there were various involvements (BTW including birds and conservation). Also I needed to read/re-read up some optics material before answering. I thought a couple times before to write and send this but could (did!) not get down to it.
CA due to loss of acuity in the user of a binocular. I am not aware if that is known. I am afraid I am not able to figure that out. May be it is possible due to some change in the shape or the material of the lens of the eye.
20/20. This figure was first assigned to this acuity in the past in circumstances that I cannot remember too well but explained this forum. Acuity sharper than that is common/very common. It seems to me that several/many who write on here are at about 20/15 or better. I had thought that correcting mild or middling myopia (short-sightedness) to one's "potential" acuity with glasses or contact lenses is always possible if no other problem intervenes. It seems that most opticians in many countries routinely do not test beyond 20/20. If this is so in your case then your acuity may be better than that.
CA due to incorrect IPD or focus. Mention of it in these forums is seldom due to those reasons!
Where I am it is difficult or impossible to sell a very pricey binocular if you do not like it. I have read a lot about CA in Leicas and before buying an Ultravid HD+ 7x42 wish to know some more about CA in it. I was particularly scared by Quincy88's "green fog of chromatic aberration"! Hence this thread.
My acuity is about 20/15. Among regular writers here in several/many it is keener and in several/many it is less keen than that. If that is not known and stated then (a) there is endless argument at cross purposes about sharpness of a given binocular, and (b) I am left not knowing if it will be sharp enough for me. That is why I have been proposing that reviewers state their acuity (and other relevant vision conditions).
I linked the two, CA and VA, in my last post above because I think that CA in some binocular, longitudinal as explained by Typo/David, and lateral as very fine fringing, may be visible only to those with better acuity than me.
David, thank you very much, for your explanation in my "absence", knowing of a risk in this situation, which was in fact realized. I appreciate this as I do your knowledge. Your response is of course more valuable than mine.
My thanks also to everyone who responded to me with their experiences and useful ideas. It seems to me that now, after this thread began, in other threads also CA has also been addressed more than usual, which I believe will be of help to many.
Personally, I had thought I may possibly be neurotic about CA (neurotic, Merriam-Webster basic: "often or always fearful or worried about something : tending to worry in a way that is not healthy or reasonable"). In my last "review", of the Zeiss Victory 8x25 I set down FWIW: "I am sensitive to color fringing in that it can be 'provoked' easily and here that occurs less than 1/2 way from the center of view. In actual use it was never obtrusive or even noticeable." Now I know that in the Ultravid 7x for me it will be. I may still go for it hoping I will be able to sum up as in one post above (Gilmore Girl) that I: "need and desire CA to be controlled reasonably well and I think it is in the 7x42 plus model"!