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A hard question really. Both are appealing cameras.
I used a Starlight Express Trius 694 for a few years. In my case it was on a CDK17 scope and also on a AP Riccardi Honders 305 F3.8 1160mm focal length.
So in one sense not a match made in heaven although it worked well on the Honders not as well on the CDK.
My SX Trius was an OK camera. I used to get weird little bumps in the stars at 1 o'clock and I always assumed some sort of guiding issue.
After I sold it the new owner checked with SX about it and he was advised it was blooming and SX sent a firmware update that fixed it. Wow, worth asking these questions of the camera maker.
I also sometimes had issues with fixed pattern noise. The camera worked best with simply biases. I used flats sometimes as well but vignetting was minimal with such a small sensor.
Fixed pattern noise though looked like the micro lenses. I don't know if others have had that issue with an SX Trius but I did. Usually just a bias and I didn't have that problem but occasionally as with usual calibration things don't always go to plan.
So I would prefer personally a QSI690 with the built in filter wheel and OAG. They seem to get the most out of the sensors they use. Also all in one camera bodies are the way to go as they seem to give the best autoguiding. You don't see images using QSI WSG8 cameras with wonky stars.
As to the 9mp sensor versus the 6.3mp sensor that is not as easy a choice.
Theoretically the 9mp sensor is better suited to your 100mm scope. 1.38 arc secs per pixel is a bit past the recommended 1 arc sec/pixel that Roland Christen of AP fame advises for those with average seeing of about 3-4 arc secs.
Suavi on this site has shown how awesome his 690 is with a small refractor. Gorgeous tight stars and great detail. Both will work well. The main difference I see is the 9mp has quite small wells. So does the 6.3mp though at just under 20,000 electrons which is pretty low. The 9mp is something like 12-15K electrons which is tiny. Perhaps not an issue for narrowband imaging but throw some bright stars into the image and you may get some ugly looking stars.
A counter solution is to use shorter exposures.
I must say though at 550mm focal length arc secs/pixel seems to be far less of an issue than say 3 metre focal length.
FSQ 106 images over the years are often at 3arc secs/pixel or more and look fabulous.
Still I would be inclined to go the 9mp sensor. The 695 sensor though is a safe bet as many have used it and shown it to be a winner.
The high QE of both of these especially in narrowband make them particularly suitable for narrowband imaging. Too bad Sony is not making anymore CCDs as a full frame Super HAD sensor would have really been something.
Greg.
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