152mm A+M Refractor(OfficinaStellare 1200mmF/L) using at Prime Focus ... a TeleVue 8mm Ethos Eyepiece without and filter and a RebelT7i modified UV-IR @ Hutech using the WB Custom-icon as a BlackCard image for the 'color balance' in the DSLR . This image here is to demonstrate an un-calibrated 'light' frame . What I saw in some images like of a far distant tower pole during the daytime was large dust donuts and small black specks . I also had to use on a 'single' image of the tower pole ... in MaximDl Pro V6.16 was the 'Auto Flatten Background' which removed the slight vignetting around the perimeter of the image and being it was a short 2.5sec exposure because it was starting to get a little darker as compared to bright daytime and it worked , but the dust donuts were still there . So , on March 29 2022 I thought that being it was clear and the would be clear , I made 'Flat' frame with the 8mm Ethos as eyepiece projection and without using a 'pin' or 'white' shirt to cover the Telescope . I could see the dark specks in the image and the large dust donuts and a smudge with a short ' 0.05 second ' exposure at ISO800 . I then took the DSLR off the eyepiece adapter and I cleaned the 'sensor' with a mixture of distilled water and 90% isoprphyl alcohol and a q-tip and other q-tips to dry it to look clean . I attached the DSLR to the eyepiece again and I tried another exposure ... the specks and large dust donuts were still there ..!! ? . I cleaned the 'sensor' again and the 8mm Ethos glass and I did another exposure and the same artifacts were there . I realized they weren't on the face of the 'sensor' or the glass of the eyepiece directly in front of the DSLR ... maybe they are on the other side of the eyepiece glass or the other side of the 'sensor' glass or embedded in the 'sensor' glass during manufacturing and they can't be removed .... except with the use of 'flat' frames that show the artifacts existing . I did eight 'flats' and eight 'darks' for each ISO at the ISO's I use as ISO800 , ISO1600 , ISO3200 , ISO6400 , and ISO12800 . I didn't move the DSLR during this during a blue sky day and I imaged at night for the M1 and NGC2392 and NGC6543 . I did NGC2392 which is this 200secISO800 FITS 'light' frame , one I did a "Convert Color" and the other I did the "Calibrate" with a DarkMaster the was Average and Auto-Optimize for Scaling .... but when I used the DarkMaster which still has the Bias included in it on the 'flats' for the FlatMaster , there wasn't any data in the FlatMaster . I tried making a FlatMaster without any DarkMaster and when I did a "Calibrate" the image was removed and the FlatMaster was the look of the image and total loss of the real 'light' frame . I tried for the Darkmaster 'calibrating' the 'flats' to make a FlatMaster with 'Auto-Scale' and that didn't work either . Then I did the 'flats' again with the original DarkMaster and this time I used the 'None' for the Scaling and the FlatMaster looked like a 'single' 'flat' frame . I did a "Calibrate" with the DarkMaster and the FlatMaster as 'None' for Scaling and the 'light' frame wasn't damaged . Both images were done with "Convert Color" , and then "Color Balance" with the 'Mouse' for 'Background' which made the background color look more normal . Then I did a "Resize" as 3.72microns to 6.5microns and then a Bin2 . I then used the "Kernal Filter-GaussianBlur to smooth the background around NGC2392 using 'pixels-restrictions' from 500 the about 2000 and Radius: 2 and Feathering: 3 which smooths good enough . I put the two images at Max-Val 'screen-stretch' and I used the "Digital Development-GaussianBlur: 1.0 and the two 'check' boxes 'checked' for 'Auto " ; then the "Color Smoothing as FFT Low Pass and FFT Hardness as Hard and Weight % 25.00 " . And these two JPGs show their differences . The 'not-calibrated' JPEG has distortion in the background and the 'calibrated' JPEG shows a smoother background without the distortion . << I think if I try on another clear blue sky day using the Telescope and then the RebelT7i using a 2in. 'nosepiece' to do a Prime Focus shot and with a 'focus' position at a far distant horizon object and the back at the blue sky facing away from the Sun ... some 'flats' without a t-shirt cornering on the front of the Telescope to then check the 'flat' frame for the above mentioned specks and large dust donuts .... and if they are there that means they are behind the 'sensor' glass and they can't be removed ... except with the use of 'flat' frames like mentioned above . It might also be possible to use this type of 'flats' on any Configuration without having to make then at a Configuration because with a mild 'flat' frame that mainly reveals the artifacts to remove them might be an all purpose DarkMaster and FlatMaster 'calibration' technique that might not add unusual vignetting to a 'light' frame using different PowerMates or eyepieces ... but something you always use might need it's own 'flats' if the spacks and dust donuts can be seen using them especially if you know the artifacts are seen at just Prime Focus without any Flattener glass or filter .>> Just by using the "Auto-Flatten Background" on thick stacked images might only be putting a large donut artifact of it's own and can't be used . If the 'calibrated' image here also does that to other 'light' frames it might be worth trying it yourself . x +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Some added info if you have computer problems that might work... Fixing installation files with DISM To use DISM to repair corrupted system files to increase performance and stability, use these steps: Open Start. Type into the ' Type here to Search ' for Command Prompt , do this and close the command and repeat with the ' Type here to Search ' and look for the ' Command Prompt app ' and then right-click on the ' Command Prompt ' tab and select from the droplist for ' Run as Administrator ' and the black page will appear with certain info typed in it ... as C:\WINDOWS\system32> and then add to that by typing next to it DISM /Online /Cleanup-image /Restorehealth after doing this it will look like this ... C:\WINDOWS\system32>DISM /Online /Cleanup-image /Restorehealth then press the Enter key on the laptop and the command will run.. it will take awhile .. till finished.
