I won't be getting the CCDT67 until I have a smaller sensor. I think it would heavily vignette my 5D III, and I can no longer afford to get a CCD this year. I'm tapped out (and then some) for a while. I am probably going to get the TSRCFlat2 and TSOAG9 for EOS, which has a 45mm clear aperture, which should let me image at 1625mm. That's going to be pretty deep, so it will be interesting to see how well I can do with that.
That said, imaging at 1625mm with a full frame and tons of megapixels is not really going to be all that different than imaging at a shorter focal length with a smaller sensor and fewer megapixels. I can always just downsample my images, and since I'll be oversampling my average seeing by about 4.2x (and better seeing by about 3x), downsampling by 50% should produce some excellent quality results. The only thing I'd be missing would be mono and the ability to use custom filters.
I actually started imaging Coma Cluster at 840mm f/5.6. I only have a handful of frames that I'm pretty sure are junk, but it seemed to be a nice field. I was imaging Markarian's at 840mm as well, but I think I got the orientation wrong, so it did not fit the frame well. I kept imaging it, though, as I figured maybe the odd framing might actually make it unique enough to be worth the effort...however with the weather, I may well not be able to finish either.
Edited by Jon Rista, 23 April 2015 - 03:29 PM.