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Old 30-05-2016, 02:03 PM
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Shiraz (Ray)
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Shiraz is offline
Join Date: Apr 2010
Location: ardrossan south australia
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Originally Posted by codemonkey View Post
Nah, the graph is the plotted relative QE. The absolute is not published, and I believe it's non-trivial to determine? That's what ZWO have said anyway.

Jon's post on page 47 says If we assume we gather about the same charge per unit area, then we might gather 20.2e- total (object and skyfog) per 5.4 microns square in a short exposure of say 60 seconds.

That assumption essentially says "if we assume they have the same QE". The 1600 is assumed to be pretty much bang on with the kaf-8300, with different relative differences, but it's still assumed, no one actually knows.

Thinking about the whole SNR thing though... read noise adds in quadrature in an image. If we take zero gain on the 1600, we have a read noise of about 3.6e-/s. Squaring this we get 12.96. I measured my 674 at ~5.45e-/s, which gives me a squared value of 29.7

If my understanding is correct, that means the absolute QE would have to be (12.96/29.7 =) less than 0.43 of the 674 for me to be "worse off" in terms of SNR. So I think I'd actually still be ahead here, unless the estimated QE of the 1600 is waaaay off. Keen for someone to correct me if I'm wrong here!
I think that all applies if read noise is the limiting factor. If sub exposures are long enough that shot noise buries the read noise, then QE wins out. The 674 is still a very effective chip, especially for Ha - it just needs much longer subs than the 1600 (sub length varies as RN^2).
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