CCD versus CMOS imagers

[Niall Saunders]

OK - I know that this topic is easily capable of being highly contentious - but what are the perceived pros and cons of CMOS cooled imagers versus an 'equivalent' CCD imager?

For some reason, I have always believed that CCD technology was a more robust solution for an imager, and have never considered anything else for my main camera. And, because of that, I am guilty of a very blinkered approach, and would like to hear the comments of others - preferably with rigorous evidence to support arguments for, or against, one imager type or the other.

[Geoff]

https://www.atik-cameras.com/news/difference-between-ccd-cmos-sensors/

[Niall Saunders]

Hi Geoff,

Thanks for that link - it certainly provides a good starting point.

I'm going to reproduce the end-of-article summary here, so that it might be easier to discuss:

CCD - Pros	CCD - Cons	CMOS - Pros	CMOS - Cons
Very little signal added by other circuits on CCD			Amp glow
Binning to modify pixel size			No on-chip binning
High quality ADC			12 bit ADC can limit image quality
Pixel to pixel reproducibility			Variations in linearity and sensitivity between pixels
	Expensive	(Cheap due to economies of scale)
	Slow to readout	Fast to readout
		Low read noise at high gain settings

As far as I can see, in simplistic terms, the CCD technology comes out ahead of the CMOS equivalent - especially for deep-sky (long-exposure) imaging. Certainly, if the aim is to take mostly Planetary (short-exposure) images, then CMOS technology would seem to be the way to go.

Food for thought?

[RickS]

As far as I can see, in simplistic terms, the CCD technology comes out ahead of the CMOS equivalent - especially for deep-sky (long-exposure) imaging. Certainly, if the aim is to take mostly Planetary (short-exposure) images, then CMOS technology would seem to be the way to go.

Hi Niall,

I'm a long time CCD user (KAF-8300, KAI-11000, KAF-16803) who has just started playing with CMOS cameras (ZWO ASI1600mm and ASI294mc.)  I think neither technology is generally superior at present.  They just have different strengths and weaknesses and are more suited to different types of use.

What attracted me to the ZWO CMOS cameras was that they are relatively low cost, small and light-weight, have smallish pixels but quite a lot of them, good QE and very low read noise at high gain (the trade off is low well depth.)  I'm planning to use these cameras with camera lenses and small refractors for wide field work.  With such low read noise you can do large numbers of short subs and you don't need to guide well... or even at all at short focal length (I'm using a Star Adventurer.)  For this application CMOS is perfect.

I won't be retiring my big CCD cameras any time soon for DSO work on my big scopes, of course...

Cheers,
Rick.

[Niall Saunders]

Hi Rick,

I think you are echoing my sentiments exactly - there is no "one size fits all" solution.

However, my desires are to image DSOs, on a rock-solid mount that can be accirately guided with ease, using a large aperture, longer focal length tube. So, all things considered, it does seem that a CCD solution is best for me.

If I was going to do planetary or wide-field, short focal length, imaging then I might have considered the CMOS solution, and would also have then taken advantage of USB-3 transfer rates to download the huge quantity of data that might be generated. That said though, when I used my existing CCD imager on an f/4 Newtonian astrograph I found that the corrected-coma and vignetting were so bad that I could really only make use of the central one-third of the available field. But, with a much smaller imaging chip I didn't have these issues, so I abandoned the whole wide-field game, and went back to what I liked best  (an f/8 light-bucket !).