SharpCap Forums

Hello Robin,

a feature I'm still trying out. It works nicely with brighter stars. I've also noticed that the low brightness stars, which almost disappear in the noise, are ignored by the function. They are probably below a set threshold, or something similar. However, in occultation observations, it is conditions like this ( faint, fading stars ) that we are trying to adjust the exposure length for, given the highest possible time resolution. Precise photometry is not needed for this, an approximate calculation would suffice I think. Would it be possible to define a range of luminosities over which stars would be registered/measured ?
I have made some recordings that I would like to evaluate in the shortest time possible, where I would compare the outputs with the outputs of the photometry program. I'll be sure to share the results.

But I would like to ask if there is a possibility of a feature like "buy me a coffee" here on the forum or somewhere, because I feel the need to reciprocate for your approach and the work you are dedicating to this.
Thank you.

Peter

As an aside from the photometry topic, this feature is brilliant for truly knowing how bright (from a camera/histogram/ADU perspective) single bright stars are when they may not be visible crawling along the bottom of the histogram, or barely detectable as clipping at the far right of the histogram.

Cheers, Chris,

Hi,

I think adding the ability to vary the sensitivity of the star detection will help with picking up the faint stars - at the moment it just runs with the default settings as I didn't have a chance to build any UI to tweak the settings yet.

I would be very interested in seeing comparitive results with other software - I'm happy for the SharpCap measurements to not be perfectly accurate, but it would be good to be correct to within 20-30% rather than out by a factor of 5!

cheers,

Robin

Hi Robin,

What an exciting development! I have only just latched on to this thread and am trying to catch up....so just checking my understanding..

Presumably the prototype display that you show is your vision of what we might see as the continuous 'live' screen when the photometry function is run? It looks good and informative.

So ..trying to imagine how it might be used for following short period variable stars or occultations for instance ...

Would the outline work flow be..

1) the program (or preferably the user) initially picks say 5 stars from those on the screen - say the variable plus four nearby comparators
2) the user then sets up gain and exposure time etc. so that the starting data values are all fall within a sensible range
3) then start continuous running so that new values add to a growing data file of time versus each stream of data
4) datafile saved at intervals ?
5) Also live graphical display (as already for drift etc.) of selected parameters changing over time ?

As you say ..surely perfect absolute accuracy of each individual data point is not so important so much as the detection and timing of changes.

Anyway thanks so much for working on this

Tim

Hi,

as promised, I tried to compare the outputs from SharpCap and MuniWin.I used the stacked image ( .fits , file type ) of NGC 891 because MuniWin works with that format. In MuniWin I used the "Quick photometry tool", which like SharpCap is used for quick/overview photometry ( see attached image ). Please judge the results for yourself. Personally, I think the new SharpCap tool is well on its way.

ChrisR Oz wrote: ↑Fri Nov 26, 2021 4:42 am As an aside from the photometry topic, this feature is brilliant for truly knowing how bright (from a camera/histogram/ADU perspective) single bright stars are when they may not be visible crawling along the bottom of the histogram, or barely detectable as clipping at the far right of the histogram.

Cheers, Chris,

That is a very good point! I have usually found myself just trying to guess quite how short an exposure time needs be to avoid blowing out some star or another within a field - for example as part of a HDR composition - and even the current incarnation of the new feature solves that problem.

@Tim,

the sort of steps that you mention (selecting stars, logging data) might come in the future - for now this is very much an evolving feature with simple things coming first. Right now you can use the selection tool to only measure stars in a particular area of the sky. In next weeks update you will be able to adjust the star detection sensitivity and also what data is displayed. Beyond that logging (ideally without needing star selection if I can work out a way to make that robust).

@viator

Thanks for the comparison. If I am reading it right then the sky background and the net intensity of the star have come out very similar between SharpCap and Muniwin (within a few percent). The peak ADU is different - I wonder if SharpCap is displaying the value with the background subtracted (which isn't what I'd intended). The difference is roughly the background level.

I will try Muniwin myself to explore this further.

cheers,

Robin

Hello,

Always clouds, but some lights outside ... It looks good, see picture. Only some ideas:

> "Max Star Count" in steps of 1, not 5
> Describe (mouse over) also the several options of "Star Data Display"
> Make it possible to show "FWHM" + "Est. SNR" allone
> At start, the selection area is _very_ small and a bit hidden in the frame's upper left corner (mouse drawing possible?)
> Selecting stars by mouse?

Cheers

Christian

admin wrote: ↑Sat Nov 27, 2021 11:09 am @Tim,

the sort of steps that you mention (selecting stars, logging data) might come in the future - for now this is very much an evolving feature with simple things coming first. Right now you can use the selection tool to only measure stars in a particular area of the sky. In next weeks update you will be able to adjust the star detection sensitivity and also what data is displayed.
cheers,

Robin

Thanks Robin, It is already useful in fact and will try it and feedback when there is a clear night. Tim

Hi Christian,

thanks for the feedback - I have made the changes except the selecting by mouse (which is complicated and needs thought). Additionally, I have changed the SNR calculations to include the noise contributed by the background electrons as well as the star electrons, which I think is more accurate.

cheers,

Robin