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that's even better for checking the model assumptions.
The tables are based on generic scope assumptions that are close enough for most purposes, but re-did at gain 90 for your Newtonian scope and a sky of 19.72. the model says that, with bias, you should see 361 ADU in 1 minute. You recorded ~ 300 ADU in 1 minute. If your figure includes the bias, then the model is overestimating by 20% or, if your figure does not include bias, then the model is underestimating by <10%. Either way, in view of the wide range of possible unknowns, this is a good enough indication that the model assumptions are doing a reasonable job of capturing the behaviour of the camera.
You could confidently drop your gain90 exposures to 1 minute if you wanted to. The offset is required to stop read noise driving the signal below zero - an offset of 20 (= 80ADU) should do that for all reasonable camera settings.
interesting and good fun. thanks again. cheers ray
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