left flank and zoom in the histogram

[Chara]

Hi, there are many many posts in the forum recommending a shift of the left flank of the histogram curve away from the vertical axis with zero ADU value
(e.g. viewtopic.php?f=9&t=1209&start=59 i.e. post 60 by admin).

This shall be accomplished by adjusting the brightness variable for my case of a ZWO ASI 071 sensor (black level/offset for other sensors). If I understood it correctly, then the 'read noise' histogram curve is the first candidate being close to the mentioned zero ADU value (or even partially negative), since negligible thermal noise and no photon signal contribute. Also a 'dark' histogram curve could exhibit a similar appearance (especially for cooled sensors). I attach a screenshot of a read-noise-histogram (exposure 1 millisec, gain 302, brightness 80) and the .txt file of the corresponding single capture.

I find it difficult to judge the resulting histogram flank, because the read noise curve looks very thin in the histogram for smaller gains (brightness already set to maximum). Increasing the gain increases the visibility of the left flank, but high gains may be undesirable, if large full well capacities are needed. Therefore I would like to learn whether there exists a SharpCap command/click increasing the visibility of the left flank by zooming onto the left region of the histogram (neglecting the representation of the large ADU values for that moment). I have in mind the outdoor situation (which hopefully will come for me in due time), where I would not like to copy the histogram into another program (e.g. microsoft word) and do there a cut and a zoom, then switch back to SharpCap and so on.....

In viewtopic.php?f=23&t=487 post 2

one can see a histogram curve (the first one) which I would like to see on my laptop too with a free left flank. Which kind of image (dark, read noise?) do we see in that histogram (obviously not flat, probably not light)?

Many thanks in advance, Albrecht

[admin]

Hi Albrecht,

you have two ways to deal with this...

Right now, in SharpCap 4.0 you can turn on the option (in the 'Saving' settings) to save the histogram in CSV format alongside capture files. Then simply save a single frame to disk and you can then open the CSV file in Excel or some other program to inspect the data.

SharpCap 4.1 (currently in beta testing - see the Beta testing forum for discussion and download links) has a horizontal zoom option for the histogram that should help, giving you a scrollbar to scroll horizontally - as shown below.

Capture.JPG (46.13 KiB) Viewed 561 times

thanks,

Robin