View Single Post
Old 27-06-2019, 03:49 PM
Shiraz's Avatar
Shiraz (Ray)
Registered User

Shiraz is offline
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,823
Originally Posted by Imme View Post
An old thread back to life I know......however this seems to be the 'goto' advice on the web.

Just moving in to NB and have done a few tests the last couple nights however my stars are being blown out significantly using far less than recommended exposure times.

As I said, new to NB, so a question - should I expect the vast majority of stars reading at 65K+adu when reviewing subs on SGP?

Using the table I ascertained I needed a 30'ish minute sub using an F6.7 with the asi1600 set to 200 gain/50 offset. (Sky is easily in the 21+ mag range and picture taken pre moon rise). To be honest 30 minutes scared me so I went 10 as a trial.......the result, about half my stars were saturated and I had a background ADU around 3000 (bias subtracted - value 180)

I cant think what a 30 minute sub would end up like!

I'm thinking tonight I will work out exposure times based purely on background ADU rather. If I recall correctly I did similar with the ASI1600 OSC I used and those pics came up well.

that is a bit of a worry Jon - the tables are not super accurate, but should not be that far out.

I just checked some old ha data and, at f4 under about m21 sky, I get about 400ADU above bias for gain 200 and 10 minutes - this is consistent with the table.

I cannot suggest why you might get 3000ADU under the same sort of sky and with a slower scope, particularly if you are getting excessive numbers of saturated stars. Maybe our filters are vastly different - what do you use?

cheers Ray

Last edited by Shiraz; 27-06-2019 at 04:01 PM.
Reply With Quote