Thanks everyone for your input.
So, i understand that it doesnt matter if subs are averaged or summed, either way will produce the same S/N ratio. What i was trying to figure was, can one image deep with many short exposures, and i think i understand now - to go deep, you need to expose long enough to detect the faint objects - long exposures.
I guess a smooth image is sometimes as astheticaly pleasing as a deep image.
Short exposures wont pickup the faint objects that longer one would. You could sum, ie 2+2=4, but i would have thought this would run the risk of reaching saturation and loosing data before a desirable S/N ratio is reached (too much noise). So, sigma combine or median is used, this way S/N ratio can be achieved without pixel saturation.
See
Here down the bottom half and at the bottom.
please Let me know what you think and if you think im talking trash or hav it wrong.
thanks
Josh