A couple of winters ago, after I had gotten my C11 back from Celestron with a brand new set of optics, I had it out to test out my use of Reflectix on it to reduce thermals, dewing and basic better thermal management of the system (and the stuff did a great job too). I also had my TEC 160ED out as well. Seeing was "good" with excellent clarity. I spent a lot of time with both scopes on M42. The C11 was well collimated and the new optics are excellent, some of the best I've seen in an SCT in DPAC. Both scopes had been outside doing their thermal things for a couple of hours and I started looking around, especially at M42 when it was well placed, about an hour east of the meridian.
The views through the C11 were excellent in their own right. The E and F stars were easy with plenty of structure in the nebula. Very nice!
However, I noticed a certain extra "intensity" and "vividness" in the views of M42 with the TEC 160. The E and F stars were just as "easy" too.
So, I did a little comparison between the two, in mono-vision (ugh) trying to match exit pupils. I found a couple of eyepiece combinations that got me real there. For the C11 (F10), they were my Celestron 35mm Ultima and my Clave 20mm Plossl, giving exit pupils of 3.5mm and 2.0mm respectively. For the TEC 160ED (F8), they were my Edmund 28mm Plossl and my Clave 16mm, giving the same respective exit pupils as the C11.
The results were really interesting. At matched exit pupils compared to the C11, the image was smaller in the TEC but that intensity thing on M42 was rather ....intense, especially in the subjective contrast in subtle features and structure across the nebula and that glow around the Trap. The nebula was not only subjectively a little brighter in the TEC at matched exit pupils, but also subtly sharper and the background of space seemed a little dimmer in the TEC. That extra intensity included the Trap too.
I then bumped up the magnification on the TEC a little using my 15mm Celestron and 25mm Clave Plossls, to try to get a subjectively equal brightness between the two scopes. This was hard to judge so I guess I was close. But that certain vividness associated with the TEC remained.
I consider the brightness thing to be more associated with the refractor having the more efficient aperture through to the eyepiece and the vividness thing perhaps related to "contrast" differences between the systems, but, as I understand it, the two are also related.
Yeah, inch for inch they are very expensive and their image scales are typically smaller, but, never underestimate how effective a well made refractor can be on DSO's.