Magnitude (Measured) Annotation differences
Stacking program, astrometric (plate) solver, fits file viewer
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han59
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Hoping for some guidance here. This seems much more difficult to understand whats going on than one would hope for. I have single subs and stacked image tested both from Seestar of area around T-Crb nova. Would really like to get an electronic measurement that is dependable. I can estimate visually the photo from the Seestar but could benefit from astrometry. Anyhow, I have plate solved and Calibrated Photometry. I also have the same stacked image that i manually annotated with magnitudes taken from AAVSO star charts. Nearest and most popular stars near T Crb are 10.5 , 9.8, 7.2 and 8.4 however with Astap those stars are being reported as (measured) 11.8, 11.6, 11.2, 11.3 (database) 10.7 and 10.1 and 8.0 and 8.5. I dont know how i can possible understand that T Crb reported as measured 11.6 to be correct unless this is the B Band... but I dont know where to choose any different band for that matter. Can you provide any insight into what I am doing wrong here. Are these star database magnitudes being reported properly and how do we know unless able to check against another source but with so many bands and it not being specified or at least i dont know where to check. Perplexed. Thank you I have included the fit file and png labelled for any reference
here is the png manually labelled from AAVSO source
Hi Ken,
For photometry there several problems with your image:
1) Saturation. Most brighter star are saturated. The value is above 60000. This will clip the star flux value to a lower value and therefore increase the magnitude.
2) Debayering. The image is debayers to colour. This will spoil the measurement more.
3) The images seems no linear stretched. See header info below.
HISTORY mean stacking with winsorized sigma clipping rejection (low=3.000 high=3
HISTORY .000), additive+scaling normalized input, normalized output, no image we
HISTORY ighting, unequalized RGB
HISTORY Autostretch (shadows: -2.80, target bg: 0.25, linked) With
Stacking should be a less of a problem but ideally for photometry you should stack mode average and not mode sigma clipping.
I'm sure you can do photometry with your Seestar. But try not to saturate the brightest stars or just defocus a little. Secondly best practice is to use the green channel only. If the Bayer setting is set you could extract the green channel (pixels) from the raw images. This could be even reported to AAVSO as filter=TG.
If you can send me a raw of the Seestar, I can have look myself. Can the Seestar produce raw images so without colour?
Cheers, Han
Thank you for your response and I apologise for my ignorance on the topic. I am just having a difficult time understanding the nuances of photometry and confirmation of my results. Anyhow, I save all my 10 second raw subs from the seestar OSC camera. I usually accumulate anywhere from 12 to 30 ten second subs for 2 to 5 minutes (not very consistent but certainly can be) I really think i just need 2 or 3 subs but can always adjust. I then stack them in Siril after calibrating the lights and debayer since its bayer patter is GRBG. Stacking uses Normalization of "Additive with scaling" at the end of the stacking to rescale result in the [0, 1] range. I would be open to exploring stacking of these subs in your program if you believe it would be for consistent for debugging. I also just do a quick autostretch in siril as a post process step as well as pcc with platesolve. I would have thought labelling the stars with the database magnitudes of know brightness would allow me to visually estimate better the magnitude of T Crb but really dont know what band to report that in. I do not believe the seestar can produce raw images without color. As far as i know, I should be able to stack just the green channel (I need to debayer first I would think though) ... more questions than answers I am afraid.
If you have to Debayer (using GRBG) your images in Siril,then you should have already raws.
Easiest way tot process is to load them in the ASTAP photometry tab. With the popup menu you
1) calibrate
2) extract the green sensitive pixels. (if GRBG or AUTO) is set in tab stack method. Auto is only possible if GRBG is specified in the header.
3) You could stack them in groups or stack them all
All in the popup menu of of the photometry tab.
Han
Perhaps I need to watch a bunch of youtube videos. I selected the Photometry tab in the window that popped up after selecting stack menu item. then loaded my most recent session of 31 - 10 sec subs (darks by default are created and applied in realtime by the Seestar prior to saving the subs) then in popup I selected calibrate . yes the bayer patern is in the header ... this was the output from the calibration ... I am afraid to state that Im not sure of next step 12:35:28 Stack method Calibration only. No de-mosaic
12:35:28 Analysing lights.
12:35:28 Grayscale stack (classify by light filter unchecked)
12:35:28 Stacking (Calibration only. No de-mosaic), HOLD ESC key to abort.
12:35:28 Calibrating individual files only.
12:35:28 █ █ █ █ █ █ Warning, could not find a suitable dark for 10 sec, temperature 19°, gain 80 and width 1080! De-classify temperature or exposure time or add correct darks. See report in column ISSUES in tab dark.█ █ █ █ █ █
12:35:28 █ █ █ █ █ █ Warning, could not find a suitable flat for "IRCUT"! De-classify flat filter or add correct flat. See report in column ISSUES in tab flats. █ █ █ █ █ █
12:35:28 F:\EAA\SeeStarS50\MyWorks\IC 4587\IC 4587 sub 202406100150\Light_IC 4587_10.0s_IRCUT_20240610-013505.fit No compatible dark of flat found or is already calibrated!!!!
12:35:28 Calibration of the individual files is complete. New files are posted in the results tab
12:35:28 Completed. Resulting files are available in tab Results and can be copied to the Blink, Photometry or Lights tab.
You could skip the calibration for first testing.
But if you want to calibrate then load darks in the dark tab, load flat in the flat tab and flat-dark/bias in the flat-dark tab. Unselect all classify check-marks. See attached.
Then try again. After that extract the green channel using the same popup menu. Then you could select all files in the photometry tab and stack them to one image using again the same popup menu.