Quote:
Originally Posted by gregbradley
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.
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Greg,
Thanks for your input , personal experience and advice
Well received
I’m fortunate to have a camera like the 2600MC which is similar to the QHY 268C
I’ve always had some vignetting issues imaging in Sydney but since I got back from my South Coast dark site after nearly 4 months , the problem is more visually evident and now I realise that I need to use calibration frames to clean up my pre processed images. It’s getting hard and harder to image under Bortle 8 skies and neighbours either side with 2 story homes , flood lit yards , bedroom lights blearing through windows with no blinds and external wall lighting most of the night
Fortunately the 2600MC has the best specs you could ask for in a OSC whilst imaging from a such a challenging (poor) location in Sydney
Low read noise
Almost negligible dark current
FWD 50,000e
No amp glow
QE of +84%
High dynamic range
And so on.....
I’ve never had any banding issues , excessive noise or bloated stars ( even using my L Extreme filter) from this camera. I’ve always dithered every sub from 90sec up to 300 sec, I’ve stacked with and without darks and haven’t noticed any discernible difference
Hopefully using Flats ( with Flat Darks ) will minimise vignetting and provide a more even flat field , plus mask those pesky dust donuts
I’ve got some work to do over the coming weeks to incorporate calibration and hopefully get some improvements
Won’t be heading back down south until November/ December , unless we are hit with more lockdowns , the future is always an uncertainty
Thanks again
Appreciate it
Cheers
Martin