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Old 04-09-2014, 11:07 AM
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strongmanmike (Michael)
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strongmanmike is offline
 
Join Date: May 2006
Location: Canberra
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Quote:
Originally Posted by RickS View Post
A good example would be a narrowband sub with a sensor like the KAF-16803. The signal (including sky glow) will be relatively small and in a 5 minute sub the read noise from the camera will swamp the shot noise from the target (and you'll incur that read noise 6 times.) A 30 minute sub will have much better SNR than a stack of 6 x 5 mins.
Quote:
Originally Posted by Shiraz View Post
if you have high read noise and low QE, you need longer subs. eg, a system with an 11002 would maybe need 30 minute subs, but an equivalent system (aperture and sampling) with a 694 could possibly only need 5 minute subs, since the 694 has high QE and low read noise. In typical systems, an 11002 would be next to useless with 5 minute subs, but would work fine with 30 minute ones. The main driver is the read noise and the sub length scales with the square of the read noise (all else being equal). If doing narrowband, use subs as long as is practical, regardless of equipment.
Thanks Guys, just wanted to have it spelled out, there seems to be a lot of confusion over sub length and when one actually really needs to do very long subs. For me unless one is using a narrowband filter especially the very narrow models (3-6nm) the difference the very long subs make may well be unoticable..? unless you have a very noisey camera?

Mike
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