At the current 20,000 deep space long exposure images are not possible at that well depth.
Long exposure images are not necessary to get the same SNR, though. The read noise is 3.5e- vs. 9e- in the case of the ASI1600 vs. KAF-16803. The total noise term added to other noise terms is then 12.25e- vs. 81e-. At the same image scale, that is a huge difference. Long exposures would be totally unnecessary with the ASI1600. Now, I am not saying that the ASI1600 is a replacement for the KAF-16803. Certainly not. However it is a little naive to say that it is not possible and "therefor bad" (in the implication) that these sensors with smaller pixels can't be used properly for astrophotography.
Considering the small pixel size of 3.8 microns, having a 20,000e- well depth is actually quite impressive. Compared to the 5.4 micron pixels of the KAF-8300, which has 25,500e- FWC. In terms of pixel area, the KAF-8300 is over 2x larger, yet only has 1.275x more well capacity. It also has significantly more read noise (7-8e- in specs, 9-10e- in actual real-world measurements). If the KAF-8300 with a "mere" 25,500e- FWC, or a Sony ICX834 with a mere 9000e- FWC (!!), are more than capable for astrophotography, then the 20,000e- FWC of the ASI1600 is also more than capable. It is not CCD killing, but more than capable.
Combined with the low read noise, and you simply do not need long exposures. I am expecting to do 5-10 minute narrow band exposures at a gain setting of 60 or at unity gain with the ASI1600. At unity the read noise is only 1.75e-. You simply do not need 30, 45, 90 minute exposures in that case for most NB objects. There might be a few exceptions..OU4...however even in that case, I suspect the ASI1600 can get away with shorter exposures with the same SNR, or use exposures just as long for even better SNR, than most existing CCD cameras for that object (at a given image scale).
Edited by Jon Rista, 09 May 2016 - 01:34 PM.