Quote:
Originally Posted by Startrek
I’ve never had to use darks , flats and other calibration frames at my dark site ( Bortle 3 ) on the South Coast as vignetting and gradients ( minimal ) are easily handled by my processing software Startools ( with or without NB filter and regardless of exposure lengths ) as this camera has almost zero amp glow and almost negligible dark current at -10C.
However since returning back to Bortle 8 Sydney skies ( with neighbours backyard and side flood lights on all night ) recently after being away for nearly 4 months , the Vignetting , dust donuts and gradients are a real problem when imaging targets like galaxies and globs etc... without a filter ( the 2600MC has a UV/ IR protective window , so in effect a Lum filter ) Even using the L Extreme filter requires additional work in processing to minimise these issues but no where near as bad as without a filter.
So now I’m going to have to take Flats to help mitigate these issues , something I’ve never had to do before. Also I believe the Skyglow in Sydney is getting worse year by year which is so evident.
Question: In regard to my 2600MC should I be taking Flats and Dark Flats to Calibrate in DSS or just Flats only.
In addition,I’ve read in a few forums that Bias frames are not usually required in CMOS cameras like the 2600MC , they are more useful in the older CCD type cameras
Any advice on the above would be very much appreciated
Thanks
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The advantage of bias frames is to be able to scale your darks. That means each frame is measured scaled to match. That way a 10 minute dark could correct a 5 minute exposure.
I use same length exposure darks but tend to only use 2 exposure lengths - 300 and 600 seconds.
As far as flats go I subtract a bias from the flat and that is working fine.
In fact I treat my QHY600m the same as my CCDs in all ways and its working fine.
Lower model sensors with amp glow and perhaps oddball issues like uneven flats mean more care is needed with calibration files.
I have even used calibration files from a different read out mode with different gain and offset and it still seemed to work.
But my opinion is for best results use exactly matching calibration files with same temperature, same exposure length, with flats, bias and darks plus
same readout mode (for QHY) and same gain and offset.
So a couple more things to make sure they are the same compared to CCD.
On some of my scopes (AP RHA) I don't get vignetting even with the full frame sensor so flats are not super important. Darks also may not be cleaning much if you use dithered subs. But dithering is also important as there are some random hot pixels with these CMOS sensors it seems and that cleans them up.
I have not seen horizontal banding cause any issues so far with the settings I have settled on except maybe a dim Ha sub and I was only after the small amount of Ha in a galaxy shot. So it was easy to make it go below visibility.
All in all very clean and easy to uses sensors. Only caveat so far is to not blow out the star colours which can occur easily compared to CCD where the star colours retain more easily and tend to be more colourful as a result. Its a result of the high QE of the CMOS sensors and the relatively smaller well depth.
I see these sensors in 2 tiers. Those with amp glow and less than 16 bits and those with no amp glow and 16 bits. These are like superior CCDs.
The amp glow sensors are still very very good but simply not in the same league for ease of use. Amp glow is another thing that can go wrong in an already complicated game.
Greg.