The Smart Histogram only seems to have two options, either to target unity gain or maximum dynamic range. This seems to be at odds with how many people use SharpCap, i.e. with higher gain to get shorter exposures with lower read noise, particularly for very faint objects like galaxies. Can someone comment on why there is no option to target minimum read noise, for example? Or to target a maximum exposure length, for example because of guiding limitations? It would be very useful, for example, to know what is the optimal gain to use for your camera and background level if you are limited to say 30s exposures by your guiding.
Thanks for your time and thoughts.
Smart Histogram choices: Target Unity Gain or Maximum Dynamic Range
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Re: Smart Histogram choices: Target Unity Gain or Maximum Dynamic Range
Hi,
there is no real need to target minimum read noise, since once the read noise is 'low enough' compared to the shot noise in each frame there is no real gain to be had from moving to lower read noise. In fact, going to the lowest read noise is usually not desirable as it is very often at the camera's maximum gain value, at which point you will find...
* The FWD is very small, limiting maximum exposure length to such an extent that
* You end up with vast amounts of data to process
Once you have moved from minimum gain down the steep downward slope of the read noise graph towards the flatter part, you have had most of the benefit that higher gain / lower read noise can bring - further gain increases past that point hurt you in terms of loss FWD, reduced dynamic range, etc. The 'Maximum dynamic range' option takes all of this into account and moves down to lower read noise just enough to get the maximum benefit.
Finally, note that just how far up the gain range SharpCap will go in search of the best solution is partly determined by the maximum exposure length you ask it to consider. If your mount tracks happily for 120s, so you set a 2minute max sub exposure length, SharpCap will find solutions at lower gains than if you set a max sub exposure length of 15s. This allows the settings of the camera to be tuned agains the tracking capabilities of your mount.
cheers,
Robin
there is no real need to target minimum read noise, since once the read noise is 'low enough' compared to the shot noise in each frame there is no real gain to be had from moving to lower read noise. In fact, going to the lowest read noise is usually not desirable as it is very often at the camera's maximum gain value, at which point you will find...
* The FWD is very small, limiting maximum exposure length to such an extent that
* You end up with vast amounts of data to process
Once you have moved from minimum gain down the steep downward slope of the read noise graph towards the flatter part, you have had most of the benefit that higher gain / lower read noise can bring - further gain increases past that point hurt you in terms of loss FWD, reduced dynamic range, etc. The 'Maximum dynamic range' option takes all of this into account and moves down to lower read noise just enough to get the maximum benefit.
Finally, note that just how far up the gain range SharpCap will go in search of the best solution is partly determined by the maximum exposure length you ask it to consider. If your mount tracks happily for 120s, so you set a 2minute max sub exposure length, SharpCap will find solutions at lower gains than if you set a max sub exposure length of 15s. This allows the settings of the camera to be tuned agains the tracking capabilities of your mount.
cheers,
Robin
Re: Smart Histogram choices: Target Unity Gain or Maximum Dynamic Range
Perfect. Thank you.