Sorry about the stupid question but I'm new to mono imaging. Do I need to take flats through all filters - RGBSHO.
I've seen threads saying definitely yes. Fair enough, but I'm imaging at F4 and the filters are more than 20mm away from the sensor. Surely the filter is far enough from the sensor that it'll have no effect, so could just do it on the L filter to take care of vignetting and sensor dust?
Sorry Chris, you really need to take flats for each individual filter. Not only may each filter have its own dust/marks, but the "intensity" of any vignetting will also differ greatly - the difference between the background & the vignetting on a Lum filter is vastly different to that on a Ha. Using a Lum flat on other filters will lead to overcorrection.
My TS GPU coma corrector changes the focal plane and focal point so it creates severe vignetting in my F5 Newts
Flats on all filters SHO LRGB are a must for me
Dust is less of an issue for me as my coma corrector, camera and filter wheel are permanently bolted together with darkening rings in between. I’ve never seen dust motes on my images for any filters after 18 months. It when you have to build your imaging train all the time that dust inadvertently finds its way in
Enjoy your Mono journey !!
It will blow your socks off compared to OSC
Chris, I will take an opposing view on the subject of flats. In my years of mono and narrowband imaging, I have never used flats. I consider the practice to be bordering on obsessive compulsive behaviour. My rule has always been to ensure that your filters are clean, inside a sealed filter wheel, and that your camera sensor compartment is clean, sealed, and has proper dessicant. By eliminating the flat time consumption, you can make imaging more fun. The only tools I use are a good bias and dark library, which i built over months with each of my cameras. I never shoot Bias or Darks on the nights I am imaging, I simply rely on my library when it comes time to process. I have always been satisfied with my final images. And for my purposes, including gift metal prints, the quality has been great. Save your time, and don't get caught up in the quest for perfection as defined by obsessives. If your happy with an image that is all that matters. We do this for ourselves, it's not a competition to be judged by others. Have fun.
Not only flats but darks as well - you will need to to create a library of darks for different exposure lengths - I'm new to mono as well and its not as easy as a OSC camera, a lot more work involved.
Thanks all. Let's see what happens. Martin, I've got a clean pair of socks on and an old ASI1600mm-cool I just bought from Zane ...
Calibration frames have made a big difference to my images as I have inherent vignetting due to my incredible TS GPU coma corrector that provides pinpoint stars to edge of frame.
Calibration is not a chore and doesn’t add to much time to my process, it’s part of the overall AP experience.
I use the whole calibration suite with my 2600MC and 2600MM ….,
I create a new Dark Library every 9 to 12 months in my study ( takes a day ) which cover all my exposure lengths , 2 Gain settings ( 0 and 100 ) all at -10C .
I do my Flats and Flat Darks either after a capture session or the next night if it’s cloudy ( we rarely get successive clear nights in Sydney )
Flats for one filter takes 5mins , Flat Darks take 5 mins
Im a bit OC as I take Flats and Flat Darks for each project.
Imaging under crappy heavy light polluted B8 skies in Sydney , Calibration and Dithering are a must to give my stacking in ASTAP and processing in Startools every chance of a half decent high signal , low noise , higher fidelity image that I can be proud of.
If your filters are clean (much better than relying on flats to remove dust donuts) then you can get away with one set of flats for RGB, using say the red filter only.
Not best practice but as I say it often works fine. So long as your rgb filters are clean.
If your taking new Flats for each session or project then you should be taking matching Flat Darks or Dark Flats ( same exposure, Gain and temperature)
Bias frames are sometimes used to calibrate Flats but only when Flats exposure times are under 1 sec as the resultant stacked Master Flat dark current is almost zero. In addition using Bias frames to calibrate Flats may not totally eliminate hot and cold pixels as well as Amp Glow which is common on a lot of mid range CMOS cameras.
Using Flat Darks in all cases are a safe measure to calibrate your Flats as dark current in cameras is either an unknown quantity or known quantity and can vary ( each camera has its own signature) They are the “Gold Standard” when it comes to calibrating Flats.
Believe it or not ,the high end Sony IMX571 sensor used in the 2600MC and 2600MM still exhibits hot pixels and some random telegraph noise. The noise goes down if you apply darks. Secondly the flat correction will not work properly without dark and flat-darks pedestal value. The pixels in the frames have also a natural variation in the pedestal value. Only if you have very poor skies maybe you will not notice in the images.
I take new Flats and Flat Darks for each project and keep a Dark Library for reuse around 9 to 12 months.
Once you master it, taking Flats and Flat Darks is easy and not time consuming.
A full calibration suite should not be a “Chore” and it will definitely improve your images. I’m my case I have no choice as I have severe vignetting in any case.
With OSC I took flats every 2-3 nights and matching darks/dark flats every ~6 months. I'm doing same for flats on all filters with mono now as suggested. Thanks! I did an initial run with flats from just 1x filter and it wasn't ideal.
Given the large number of calibration files for RGBSHO I've just started to have a look at Pixinsight's WBPP script. It seems to do a great automated job. And reduces confusion compared to doing it all manually (which was okay for OSC). Adam Block's YouTube on WBPP has a great breakdown of the script. The only clunky but seems to be the cosmetic correction, I've yet to sort that out ...
Thanks all for your help. Have taken my first NB shots, Tarantula, with 8" F4 newt, ASI1600. Took a while to sort out best gain/exp for this camera. Have dark flats, flats & lights (for all filters) and darks! Here's ~5 hours each of Ha, Oiii, Sii. In Pixinsight, integrated with WBPP, mure denoised, sharpened, star-removal, then a simple SHO combination followed by gradient removal & a stretch.
I'll have to learn NB processing. I haven't used Pixinsight for 6 months & have used WBPP for first time to reduce confusion. And there's a lot of new(ish) processes including gradient correction & generalised hyperbolic stretch which I've tried to use here. I have RGB for stars which I'll sort out later
Thanks all for your help. Have taken my first NB shots, Tarantula, with 8" F4 newt, ASI1600. Took a while to sort out best gain/exp for this camera. Have dark flats, flats & lights (for all filters) and darks! Here's ~5 hours each of Ha, Oiii, Sii. In Pixinsight, integrated with WBPP, mure denoised, sharpened, star-removal, then a simple SHO combination followed by gradient removal & a stretch.
I'll have to learn NB processing. I haven't used Pixinsight for 6 months & have used WBPP for first time to reduce confusion. And there's a lot of new(ish) processes including gradient correction & generalised hyperbolic stretch which I've tried to use here. I have RGB for stars which I'll sort out later
Chris,
Glad you got your Calibration sorted out
Nice Spider too
I don’t use Pi so can’t help you on that front , I’m a Startools user which has given my images so much more flexibility since switching to a Mono rig.