Hello @Henry, @Joachim, and others, Thanks for your exceptional guidance, I was able to make good progress in making a decision. I present the details below. I end with a couple of questions. I would greatly appreciate all of your insights as always!
Instead of being restricted to just the scope that I have, I decided to spend several hours at our local birding store comparing
(a) focus snaps at 60X and
(b) star-testing to the best of my ability.
The scopes that I had access to were the ATS65, ATS80, Kowa 883, store's Kowa 663M and my 663M.
(1) My focus snap ratings 60X: ATS65 > Kowa 883 > store's 663M > ATS80 >= my 663M.
(2) With respect to star tests on electric resistors’ highlights: astigmatism, spherical aberrations and coma seemed relatively easier to notice, so that's what I recorded. I repeated the test on various such highlights across a range of distances >= 100'. The results follow:
(a) The store's ATS80 copy left me with a similar distaste like my 663M copy. The diffraction rings on one side of focus was extremely mushy, the worst in this regard among all the scopes compared.
(b) The store's current Kowa 663M copy was excellent in contrast/clarity at 60X than mine. It did carry astigmatism like mine. Given that the diffraction rings were more similar on either side of focus, I felt it was better corrected for spherical aberration as well. It also had smoother focus, perhaps adding to its better performance over mine.
(c) The Kowa 883 with its dual focusser certainly showed some astigmatism and coma. However, it was a great deal better in its ring patterns than the ATS80.
(d) Finally, the ATS65 copy was a whole league better than the poor performing scopes here with respect to the diffraction rings. The focus snap was very nice.
The questions:
(1) All scopes however did have relatively dimmer rings on one side of focus, compared to the other. Why is that so?!! Is that all spherical aberration?
(2) Given that the store's current Kowa worked better than mine, I am inclined to send back my copy. But I still need to figure out if I want to take the store's Kowa as an exchange over my copy / do a return and move on to something ele. This is going to be a hard decision for the following reasons (besides the >=$600 cost difference):
(a) Moving from the store's 663M to ATS65, perhaps due to a combination of FoV, brightness and eye-relief reasons, I had a jump in the feeling of a relaxed view at lower and moderate zoom ranges (20-30X, 30-50X). However, at higher zoom ranges (50X-60X), the Kowa was more easier with eye positioning.
(b) Swaro being Swaro basically produces an image with the same color balance & characteristics as my current 8.5x42 binoculars … soo… I am worried if it would get boring after spending all that money.
(c) Moving on to the Kowa 883, this time from the ATS65, I felt the relaxed feeling doubled/tripled! At this point, it became very clear that if comfortable viewing / easy eye positioning / FoV / brightness are of primary concern, it is hard to settle with 60/65mm scopes - whoever the manufacturer is! However, this drama in the view from the 883 comes with ~1.1lb weight increase, and >=$600 price increase over the ATS. It is thus very clear the 883 is too much for us to be traveling/hiking around with.
Given the very noticeable inferiority of 60/65mm scopes’ relative to the 80ish mm scopes with regards to image quality (especially on those cloudy days) and comfortable viewing anyway, it does beg the question: should we settle for the store’s Kowa 663 for the price, and spend on an 883 or something similar for local birding? I am very confused!
Thank you for any insights you might add!
Kumar