Hi Everyone,
I am working with some images I took with my Sony ZV-E10 using a Viltrox AF 13/1.4 E lens.
What I am noticing is that when I stack my lights with darks and flats (preprocessed with bias or with offset constant) I get this weird “halo” effect in my lights stack. The halo appears to correspond to the flats but is inverted. In the flats the center is light and the vignetting is darker. In the light stack the center is dark (or clear, maybe?) and the vignetting shows up as light.
I have reshot my flats a number of times now in a number of different ways and reprocessed everything. The exact extent of the “lightness halo” changes depending on the method chosen to reshoot the flats but the effect remains:
This screenshot is with a Histogram stretch to make it more apparent what I’m talking about but it is visible in autostretch as well. Additionally, as I stretch the image this halo becomes more and more visible.
If I exclude the flats and just stack the lights with darks the halo is not there.
I carefully went through the Synthetic Biases tutorial and determined an offset to use instead of biases (bias=512) but the halo is still there so it seems to be caused by the flats (this synthetic bias version is what the screenshot is of).
The only thing I can see is that the ADU values are much lower than I have read on some blogs and forums that asserted the flats should be in some mythical sweet spot around 50% to 75% of the range … these are far below this recommendation.
Is this an indication that I’m doing something wrong or maybe just an artifact of using this lens? Should I be shooting brighter flats somehow or maybe just somehow artificially boosting the level in the flats images so they are magically in that aforementioned sweet spot but maintain the same relative falloff and vignetting shape?
My current workflow is derived directly from the OSC scripts although I have adjusted a variety of things as I have tried to work through this issue. I have tried the Linear Fit Clipping and the Winsorized Sigma Clipping so far but haven’t tried any of the others. I have also altered the sigma levels trying to keep the rejections within the .1-.5% amount recommended in one of the tutorials.
For all I know this is something that can be ignored but since it shows up in the stretching I’m thinking I shouldn’t be ignoring it.
Thank you, in advance, for any help that may be given.
edit: Of course the more I stare at this the more this halo seems to resemble the images seen in the synthetic biases tutorial; specifically the L/F and the L/(F-O) examples so maybe there is somehow something wrong with my darks processing? Will have to read the tutorial more carefully to see if this is an error in my processing.