Carl:
I have been considering using a Barlow even though I still have more to learn about using the SX-AO unit with the focal length of 2850 mm I took this picture with. One thing I would have to do is to get a very bright guiding star so I could use the SX-AO unit at a much higher speed (more than 10 frames per second). I believe it is doable.
Greg:
Yes, the QHY11 has the 11002 chip.
I have the SX-AO-L unit. L stands for Large. It has 60 mm free diameter. Vignetting is minor; just a little bit at the corners, nothing to think about.
What this big chip requires with my scope is very good collimation and to be orthogonal to the light path. I am collimating the scope, quick and easy to do with the RCX400, at the average position that I am going to take the picture. The image train is quite long and heavy: RCX400-->SX-AO--> SX-Off Axis Guider + Lodestar -->QHY Filter Wheel-->QHY11. Any flexure will be shown on the big chip.