Thread: F-ratio myth
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Old 21-02-2018, 10:41 AM
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Shiraz (Ray)
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Location: ardrossan south australia
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Originally Posted by Paul Haese View Post
Some direct experience.

12" f8 RC with SBIG STXL11000 which is about 0.76" per pixel

12' f4 Newt with QSI683 which is about 0.92" per pixel.

The image scales are not too dissimilar.

Same target to get similar looking results.

12" RC 39 hours
12" Newt 15 hours

Imaging speed does appear make a difference at similar image scales.
Hi Paul

your experience could be explained by:

sampling - the imaging time scales with the square of the sampling, so your 11002 system required 1.5x as long as the 8300 due to this alone
QE - the 8300 has about 1.4x the QE of the 11002 at Ha, so there is another 1.4x in favour of the 8300
Read noise -for narrowband imaging, you will almost always be read noise limited and there will be a significant reduction in the required imaging time with the 8300 due to its lower read noise(how much depends on sub length).

So, multiplying these factors, your Newt with 8300 should be considerably more than 2x times faster than the old system was - but much of it is down to the limitations of the 11002, not the FNo of the scopes.

cheers Ray

Last edited by Shiraz; 21-02-2018 at 11:47 AM.
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