Thank you for your reply, one more thing I have forget to mention that is I am using Mac Book Pro, Sorry about that.
I am use QHY268C Camera, I cannot control the exposure and gain.
During the day time I can see everything in 'live view' mode, but the maximum exposure time seems 5 seconds only.
At night, the 'Live View' screen is black at any exposure time or gain value, that's mean I get the same result no matter I set the exposure time to 3 seconds or 300 hundred seconds, I can only use the 'loop' to see the sky, but same as the mention before, nothing have change no matter how many second I set.
Is some setting I have miss? Can somebody help me?