SharpCap Forums

Hi, I was planning on testing the effectiveness of different strategies for taking flats on Live Stacking. For example different light panel configurations, zero gain flats vs. same gain flats etc.

Suggested process > Start of observing session take a series of flats + dark-flats, with the different light panel configurations being tested. No need to tick "apply new flat when capture complete" or "keep image files". Maybe rename the flat files eg Panel A, Panel B. Then shoot live stacks on a few targets, applying the FWHM and brightness filters, and ticking Raw Frames_Save Stacked. Probably leave pre-processing blank for now.

Then go back later, select folder monitor camera and point to the capture folder for lights for one of the targets (highlight one raw file). In the Preprocessing panel select one of the test flat files plus the dark file. Click Live Stack. In Camera Controls on the RHS panel click the Play button. When the stack is finished click the auto-stretch and auto-colour balance lightening symbols, then "Save as Adjusted". Repeat the process selecting a different flat file.

Main question - will this process accurately emulate live stacking & pre-processing from a live camera ? Otherwise I take a series of repeated live stacks of the same target during the observing session with different flat files selected....

Hi,

yes, pretty much - that's one of the things the folder monitor camera is designed for.

There are a couple of minor gotchas...

1) If you only 'Save Stacked' then you cannot adjust the FWHM or brightness filters in a meaningful way in later re-runs... You already only have the 'good' frames. If you want to do that, choose 'Save all' or 'Save except when paused/dithering'.

2) The way that the folder monitor camera works is that it initially displays the first frame - you would then typically activate stacking and press play to run through the frames, but that way the stacking doesn't see the first frame as it has already been used. You can use the 'replay frame' (circular arrow) button to re-run the first frame through stacking if that's important.

cheers,

Robin

Hi thx for that. I looked back on some live stacks where Raw frames_Save Stacked was selected in the Live Stacking Controls (I think this just means save the good raw frames, rather than save the stacked image). The folder is filled with 16 bit PNG files corresponding to the single frames. Stacking these from the Folder Monitor Camera and looking at the histogram, the images maybe have been re-scaled compared to what it looks like with SharpCap stacking from the camera live eg shifted to the right.

Maybe to emulate the live situation for these tests, I need to go to File_SharpCap Settings_Saving and tweak some settings so the raw frames are being saved equivalent to how as SharpCap sees them streaming direct from the 294MC camera ? For "save with adjustments" final stacked image, I definitely prefer PNG for later use in Affinity Photo. But for these tests where we want the stacking of raw files to be re-run using Folder Monitor Camera to test out different flat files, maybe FITS is better as the still format for the raw files ? Or ultimately to do the testing of flats during repeated live stacking from the 294MC camera to be 100% sure of equivalence....

BTW ticking "Background Subraction" "Non linear Gradient Removal" during stacking using Folder Monitor Camera does a fair job of reversing acute vignetting (no flat in use). Perhaps if flats were in use, but correction not quite perfect, Non linear Gradient Removal may give that last bit of correction. One night the flat correction was introducing a linear gradient from the side (still greaty improved vs the ugly vignette minus preprocessing). In this instance "Linear Gradient Removal" may have corrected-out that gradient... Post-processing in Affinity Photo I generally find doesnt help much with vignetting and gradients....