Thank you Rodney, Marc, Marcus and Russell
Last night I managed to capture more data and did a quick comparison as for the amount of detail gained with longer integration.
The attached image shows, from left to right, auto-stretched area in a single 10-minute sub, stack of 20 subs and 45 subs. St. dev was respectively 36.8, 8.8 and 6.7. Clearly more faint stuff shows up with longer integration.
I think now I have sufficient Ha data, so time to move onto capturing O3 and S2 data.
Thank you all for your encouragement.
Suavi