Thank you, Ross. I have two limits that drive my captures.
1) light pollution. I have not filters to Canon
2) RGB saturation of stars
And, I have lamp of street that illuminates the interior of my OTA.
High ISO with long time, I must deal with sky glow
High ISO with short exposure, I must deal with saturation
Low ISO with long time, I must deal with noise
Low ISO with short time, it is trash
It seems that to nebula, the best result is with ISO 400 or 800, but with short time.
To stars and cluster, ISO 100 or 200 and long time.
Galaxies and faint object, I didn't test yet.
At moment, I am using the information of histogram to pollution. And intuition to RGB saturation.
