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Okay, I have it figure out. It was the hub I'm using a cheap Mbeat USB 2&3 powered hub. For some reason, whenever you have more than one device plugged into the hub, it creates these 'pauses' in capturing - I assume because it's polling the other devices and multiplexing the traffic into the one USB connection to the computer. That's my theory, anyway. Presumably, all hubs will have the same issue.
Simply by connecting the camera direct to the computer I can get the following rates with a 3rd Gen Lenovo X1 and a USB3 External SSD.
At full-frame 16-bit I can get a sustained 81fps
Full Frame 8-bit gives 171fps
With a 656*536 ROI in 8-bit mode, I can get sustained 340fps.
So since I'm shooting mono, I guess my new Planetary setup will be camera plugged straight into the computer, with Filter Wheel, focuser, etc running off the hub.
Just tested this setup and it works (ie, it's not the computer's internal USB bus that is the bottleneck as shown by the fact that plugging in the hub is non-disruptive to the high speed video coming in off the ASI290).
Cheers
Markus
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