I don't know if all Borgs are the same, but I started a thread on the Borg 90FL f/4:
In quick summary:
I think the Borg 90FL f/4 is like dating a gorgeous super-model, who has some issues, requiring constant attention, but still worth staying in the relationship.
My Borg 90FL f/4 has significant chromatic aberration, which is essentially solved with an aggressive UV-IR cut filter. I own the IDAS UIBAR-III, which just about eliminates blue and red bloat. The Baader semi-apo filter works great too, especially if doing OSC, or even combined with a R, G or B filter. This is a Flickr album regarding the Borg, RGB and the semi-apo filter.
It also has a slight astigmatism, requiring precise focus, which forces me to find the spot where the stars are perfectly round, and may actually be a good thing.
For narrow-band, I believe it to be excellent. It is so light and elegant, and I love the large helical focuser with numbered divisions. making initial focusing repeatable for different filters.
The Borg 90FL with the Sony IMX 183 sensor, at f/4 is 1.4 arc-sec/pixel. So it is in a good sampling regime (for the seeing I normally get).
Feel free to contact me here or privately. I have much to say about this scope. And Ted Ishikawa , the U.S. representative, is a true gentleman, and you can't ask for better support if needed.
Edited by StevenBellavia, 10 January 2019 - 08:55 PM.