Good news for people whose mounts (RainbowAstro, Hobym, Avalon, etc) require fast guide rates.
ZWO switched from asynchronous mode guide camera captures to synchronous mode ("video mode") image capture in the v1.4-v1.5 time frame. Ever since then, the guide frame rate was limited to 1 FPS even if you set the exposure time to shorter than 1 second.
Good news is that with the v1.7 beta, a 0.5 second auto-guiding exposure time now updates at a full 2 FPS.
With a ASI290MM (USB3.0) and a V2 ASIAIR, the FPS is still limited to 2.5 (equivalent to 0.4 second exposures) with a 0.2 second guide camera exposure, but it is not likely that you can use such short exposure times anyway, if you are using near-IR guiding like I do.
I won't have a chance to try it out under dark skies for a while, but if you are seeing an improvement with autoguiding with 0.5 second exposures, this could be the reason why.
FWIW, even with ASIAIR v1.5, I already saw an improvement switching from 1 second guide (1 FPS) exposures to 0.5 second (also 1 FPS) while using a 685nm IR-pass filter with my ASI290MM guide camera.
Chen
