Thanks everyone for their input. It's good to have confirmation that the EdgeHD 11 is as lenient as the C11 as far as backfocus-induced aperture reduction is concerned -- namely, it seems to work with everything until you literally run out of in-focus. I still want to do some more rigorous testing though with my own OTA before I pass final judgement, but certainly nothing leaps to my eyes.
I have an Edge 14 but no binoviewer. I find the optical performance better closer to the recommended 146mm back and in fact operate a little closer.
Thanks Glenn for your observations with your EdgeHD 14. I'm curious though: in what way do you find the optical performance better (I assume visually) near the recommended 146mm? I understand that technically the EdgeHD correcting optics must have an optimal position, but have not spent any time testing whether this is actually visible with my bare eyes. It would be interesting to know what to look for.
With a camera it has been shown that the margin of error for sensor position in an EdgeHD system is extremely small, literally down to a fraction of a millimeter for the flattest field. But I'm not certain my eyes are good enough to distinguish that sort of difference in the field.
I am not sure that it is the same as the standard SCT. I would measure it.
About a year ago, Russ (at Denk) and I had a long conversation about this. As I recall, he told me that he did indeed have a customer that was unhappy with the apeture loss imposed by the binoviewers in low power mode.
Best to measure for yourself.
Disregard any concerns about the laser test. I have used it on four different SCTs, and all showed various amounts of apeture loss (as much as an inch and a half) tjhat alwasys started at between 160mm and 200mm.
But I recall the conversation with Russ regarding the EdgeHD 11.
Again, my advice is to measure it directly, and trust the test. You will see that if you are loosing apeture, shortenting the light path will give some back, which is just what should happen in this situation.
Not so sure at all that the Edge HD11 will tolerate back focus better than the other SCTs now, and until you or someone else measures it directly, the only think I have to go on is what Russ at Denk told me, though I think someone else was complaining about it on a forum a while back too.
Mearue to know for sure.