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Old 14-10-2011, 06:10 PM
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Bassnut (Fred)
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Qe vs aperture

Im looking at a 16801 chip (68% qe at 656nm ha nabg) and a 16803 (45% ha abg).

What kind of aperture difference is required at the same Fl to get the same depth image with the same exposure time?. (ignoring the increased optical res of a larger aperture)

In other words, what is the relationship between the qe of a cam and size of an OTA for the same image result.

That might seem an obscuRe way to look at things, but hi qe means read noise is a smaller proportion of signal, and many other advantages with a smaller OTA/OBS eg a 16" instead of a 20" with reducer which the Pme would struggle with.

I'm not sure about the overall cost diff, I suspect it would be the same, the 16801 ain't cheap, but I'm not so concerned about that.
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Old 14-10-2011, 08:10 PM
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RickS (Rick)
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From a pure light gathering POV and taking some simplifying assumptions...

Going from 45% QE to 68% QE gives an increase in sensitivity of about 1.5 times (actually 1.511111111...) That's equivalent to an aperture increase of just under one and a quarter times [sqrt(68/45) or approx 1.229].

So, 4" aperture at 68% QE is equivalent to about 4.9" at 45% QE, 12" aperture at 68% QE is equivalent to about 14.75" at 45% QE, etc.

Cheers,
Rick.
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Old 14-10-2011, 09:34 PM
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Bassnut (Fred)
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That's what I was looking for, thanks Rick, excellent.
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