I have been recently asked on a comment on performance of 71FL vs. 77EDII (because I am known for owning all Borg lenses and reducers). I have found this quick-test image somewhere on my hard-drive. It’s from November 2011 so kind of an old test. My conclusion is that again, biggest problem is helical focuser, second big problem was the bad design of the 0.7x reducer that was held in place by only 1 screw located on a side of the inner barrel which could (and also did) cause some misalignment that completely degrade the final performance, especially on a large (full frame 36x24mm) chip.
Since I did not want to spend more money on purchasing FTF and producing custom parts in order to place the reducer inside of the focuser in a smart way I have recently sold all my Borg scopes and reducers except of 77EDII F/4 SR combo (in the end I have converted to an expensive Newtonian system from ASA that brought my imaging to yet another level).
Here you can find one of the best results I got from this combo with a 34x24mm FF CCD (MII G3-11000 camera).
and the corresponding (uncalibrated – except for hot pixel removal and vertical column banding supression) light frame:
For star-field testing I am always using a H-alpha filter that shows the true shape of the stars (along with making them smaller). Using broadband filters makes the star shape differences much less apparent, but obviously works well for APO-chromaticity testing.
BTW all refractor manufacturers make the same design mistakes over and over again (I should start my own company that would deliver 100% perfect astrographs without a single compromise). Because I learned that I have to tune the refractors myself using plenty of custom parts, I have started using Newtonian systems in spite of the well known and much afraid of task called collimation. The BIG aperture and performance makes a HUGE difference in terms of light collecting. Plenty of refractors are slow (F/5 and even worse) and I simply do not have enough clear skies to make one picture in three clear nights.