I've been doing a lot of reading and a heck of a lot of talking, and I have decided I definitely want a maximum-aperture travel scope, that will absolutely be used at home and out at dark sites. I currently have an AT72EDII which is an excellent little scope for quick views and carefree use due to its relatively low cost compared to much more expensive optics, like the 90FL, and I also have my SW120ED for long nights at dark sites, or if I feel particularly inclined to check something out in my Bortle ~8.5 skies on a clear night with just a little more aperture.
Minnesota has the Boundary Waters Canoe Area Wilderness, a beautiful escape from city living, near the border of Canada. It has true Bortle 1 skies, and I would love to take a scope up there and get lost in the sky. I cannot do this with the SW120ED, but I could with the AT72EDII. However, I would love to max out my aperture and weight, for travel, and the AT72EDII isn't quite there. Thus, I have been heavily considering getting an AT92, which is due Q1 2018, which is very short (only 16.5"), but will be quite heavy as a triplet, probably around 4kg. The Borg 90FL is only 2kg(!!!) and about 17" long I believe (~400mm), so it is even more portable than the AT92, and can still be brought onto a plane as a carry-on item. Weight is a significant concern for backpacking, so the massive weight reduction is a huge plus for me.
I have found a very limited amount of reading material for the 90FL, mostly saying that it is popular among birders and imagers due to the fast focal ratio. I am sure it makes a wonderful widefield astrograph, but for the time being, I am only concerned with its use as a visual instrument. This is where I start wondering about CA in a fluorite doublet design, uncorrected like the imaging configuration. Allegedly the objective is almost the same as the Takahashi Sky90 (made by Canon Optron), but the spacing is tighter, so collimation is much less of a problem. I know some people were not thrilled with the level of CA on the Sky90/II, but others seemed to think it was good enough for such an aperture in such a compact tube.
Can anyone provide first-hand experience with the 90FL? I have half a mind to buy one and sell it if it doesn't meet my expectations, but I would like any extra feedback if possible. Should I get a different scope entirely (that doesn't involve waiting an unknown amount of time for it to appear on the used market)? Should I just learn to love the AT72EDII and get a more premium scope like an NP101/FC100DF in the next 6-12 months? I don't want to have to remove a dew shield and focuser just to fit a scope in its case so that is not an option for me at this time.
Any and all feedback is appreciated. Thanks!!