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FLATS - how effective?
Adam,
I've a question (an issue really) that I'm probably going to find the answer to experimentally, but I was wondering if you had some experience in this area.
In my recent M42 (and M45) project which I had shared with you, I had noticed what I first thought was a noise pattern that was mostly visible in the Oii and Sii masters (and also the G and B masters for M45).
I started looking at it more closely after finishing my M42/HDRMT project. It is not noise and it is, if very faintly, evident in the Ha and Lum images as well. Since it seems 'uniform' in how it appears across the filters, I was fairly certain that it was not anything on the surface of the filters in the EFW.
I checked the primary lens of the OTA (Esprit 100ED) and it appears to be a 'film' rather uniformly across the lens but mottled (that looks exactly like the 'pattern' I'm seeing in the masters. Based on it relative visibility depending on the filter, it seems to be more opaque to green/blue/OiiI/Sii spectra than Lum or Ha/R but that may have more to do with the relative signal strength of the target in those ranges rather than anything else.
I don't want to lose my current data set, so I'm going to see if a new set of flats will allow this to be calibrated out. I know it does for more obvious specks/etc but I have no idea about something like this. I do plan on cleaning the objective and get yet another set of flats going forward, but my current effort is to manage the issue in my last two data sets (and no I don't normally shoot new flats/dark flats every night).
My concern is that since it is relatively uniform is that the short exposure times in flats/dark flats with CMOS sensors (managed in NINA), there won't be much correction.
Have you dealt with anything similar?
In my recent M42 (and M45) project which I had shared with you, I had noticed what I first thought was a noise pattern that was mostly visible in the Oii and Sii masters (and also the G and B masters for M45).
I started looking at it more closely after finishing my M42/HDRMT project. It is not noise and it is, if very faintly, evident in the Ha and Lum images as well. Since it seems 'uniform' in how it appears across the filters, I was fairly certain that it was not anything on the surface of the filters in the EFW.
I checked the primary lens of the OTA (Esprit 100ED) and it appears to be a 'film' rather uniformly across the lens but mottled (that looks exactly like the 'pattern' I'm seeing in the masters. Based on it relative visibility depending on the filter, it seems to be more opaque to green/blue/OiiI/Sii spectra than Lum or Ha/R but that may have more to do with the relative signal strength of the target in those ranges rather than anything else.
I don't want to lose my current data set, so I'm going to see if a new set of flats will allow this to be calibrated out. I know it does for more obvious specks/etc but I have no idea about something like this. I do plan on cleaning the objective and get yet another set of flats going forward, but my current effort is to manage the issue in my last two data sets (and no I don't normally shoot new flats/dark flats every night).
My concern is that since it is relatively uniform is that the short exposure times in flats/dark flats with CMOS sensors (managed in NINA), there won't be much correction.
Have you dealt with anything similar?
Comments
I've not yet finished my post processing to verify completely, but the 'artifact' in the image *may* be the result of integrating all the separate exposure times for each filter into a single master for each filter.
I went back to WBPP and closed down the interval to the default 2 sec for post processing. This allowed WBPP to create a master for each exposure for each filter. I then combined those using HDRComposition, performed DBE, NXT, and BXT.
I'm working through a few different SHO palette approaches at the moment - ChannelCombination, the rather standarnd fix ratio'd Pixel Math for SHO, and the ForaxX pixel math tool for dynamic SHO. I've applied the modified SCNR pixel math tool from Bill Blanshard and created a non-linear version. I've not yet started working the colors yet but I do note (as I did as this version(s) progressed) that the mottling seen in the first WBPP version in the Oiii and Sii does not seem prominent, at least to this point.
I've also applied Russ Croman's ColorCorrectHDR tool after the stretch (and applied it to the published verion of my M42 as a comparison). I'm seeing much more detail in the HDR frame created from the HDRComposition method than is apparent from the same tool applied to the multi-exposure integration in WBPP.
The impact of the ColorCorrectedHDRMT tool vs the standard HDRMT is significant on this object. So much so, that I'm going to have to rethink how / what I do for color processing part of this target vs the original version.