I've done it! I ordered a Canon 200D - a standard off the shelf version and it will be compatible with all my existing equipment without buying new T-rings, new intervalometer, new connection leads etc. It looks sufficiently different to other entry level Canons to be an interesting proposition. For instance, as CentralDS says here ( http://www.centralds.net/cam/?p=10451 ) it is using new sensor technology where the ADC units are built into the sensor itself instead of being off sensor i.e. Canon is finally doing what Sony has been doing for ages.
As inidicated earlier, the PhotonsToPhotos testing certainly indicates that the sensor's behaviour is far closer to a Sony than any previous Canon. On the down side, PhotonsToPhotos indicates that the QE at 49% lags behind the 54% of Nikon D5300 and 59% of the Canon 7DII but the difference between the Canon 200D and the Nikon D5300 isn't huge.
One reservation I have is that the same CentralDS page indicates that it might have far more dark noise than the 80D - I can test the dark noise.
I also downloaded some sample 200D raw files from DPReview and this confirms that there is no dodgy raw data scaling causing regular histogram gaps in the R&B channels - a problem to which Nikon is prone and which can potentially cause coloured concentric banding in exposures calibrated with flats. This problem affects my Sony A7S quite badly.
In any case, I'll do a whole batch of tests on it, including read noise at each ISO, dark noise and sensor self heating over a prolonged period of long exposures. In the end, if the Canon 200D is no good to me as a back up camera I can always sell it. I'll also check the darks for nefarious algorithms such as "star eater" (I don't expect to find any). I'll test the QE relative to my Sony A7S and Canon 600D but I have no way to calculate absolute QE.
I'll start a new thread when I have some test results but the full moon needs to go away before I can take any sample astro-images.
Edited by sharkmelley, 27 August 2018 - 09:03 AM.