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Old 17-05-2016, 04:39 PM
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Shiraz (Ray)
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Location: ardrossan south australia
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Originally Posted by Slawomir View Post
Although ithe download time is probably about 40ms for full res, so, even at 1sec, not many hotons will come along while the chip is doing something else.
t all sounds really promising and there is definitely a sense of fresh breeze in terms of new technologies being made available to astroimagers, but at the same time I remain sceptical, possibly due to my ignorance...

It seems to me that the laws of physics cannot be broken - there are only so many photons hitting a sensor from a DSO in a given time. So if there is one photon per say 2 seconds from a DSO per unit of area/pixel, chances are we will miss a significant percentage of them with 1s exposures. Just speculating here though...and to clarify, with ideally zero read noise, would longer exposures help to extract DSO's signal from noise coming from the skyglow, or is that corrected with number of subs alone

Either way, those brilliantly fast and sensitive sensors certainly open doors to new ways of imaging.

Originally Posted by Atmos View Post
Suavi, you have just hit the nail on the head as to why professionals are not going to go down the path of short subs (depending on situation obviously), faint stuff! Difficult to detect at the best of times, short subs can at times leave you with more noise detection than real stuff leading to faint bits being rejected.
the full frame download time should be around 40ms (it runs at up to 23 fps full res), so the chance of photons being missed while the chip is doing something else is quite small, even at 1 second subs.

The big thing though is the low read noise, which allows you to get to sky-limited performance with short subs. One second is a bit extreme (but possible) - maybe 30 seconds would be more mainstream and still provide some significant advantages. You don't have to use short subs, but why not if there is no SNR penalty and you get improved dynamic range and all the mount advantages?

Note that short exposures are not unprecedented in the professional arena. For example, PanSTARRS has a low read noise detector (for larger pixels at 5 electrons) and is sky limited after 15 seconds - typical exposures are 30 seconds. Once you get to sky-limited, longer subs do not help you extract signal in the final image - longer subs will look better individually, but the final stack from a lot of short subs will be the same as that from a few long subs if they are all sky-limited. Longer total exposure improves things, but not longer subs.

Last edited by Shiraz; 17-05-2016 at 05:14 PM.
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