Intro to CMOS vs CCD

[SteveA]

I strongly suspect my next camera will have a CMOS sensor and been toying with the idea of something with a larger sensor than my Atik 314 for ages, but until now the cost has been prohibitive. I wasn't really sure I understood much about the difference in the two technologies, but found this nice little (non-technical) intro on the Atik website...https://www.atik-cameras.com/news/difference-between-ccd-cmos-sensors/

Steve

[Knight of Clear Skies]

I've gone down the CMOS route myself with the 1600MM Cool, as the small pixels are a good match for short focal length scopes and camera lenses. A practical benefit I'm enjoying is that I don't have to worry too much about exposure length due to the low read noise. For example, here's my mono M31 taken with 30 second unguided subs (300 gain):

It's just under an hour of data in total. Instead of spending valuable time drift aligning or tinkering guiding I was able to get on with the imaging. (To get the best out of it I should look at those things, I don't know what the optimal exposure time is.) So far I haven't had any problems with amp glow or banding artifacts, but I haven't pushed the exposure times past 60 seconds and my subs get a good "dither" due to polar misalignment.

As I understand it CCD cameras are still generally the best solution for AP, but not necessarily the most cost-effective. The 1600MM Cool appears to be a good match for my interests and the limitations I work under (UK weather and limited time/expertise to debug issues).

[Gina]

I have changed from CCD to CMOS recently and never looked back   Specifically from Atik 460EX mono to the ZWO ASI1600MM-Cool.  The latter has a larger sensor and much higher resolution and the very low read noise at shorter exposures has meant I can do away with guiding and polar alignment is less critical.  So instead of a few dozen subs of up to 20m I use a couple of hundred subs with 30s to 60s exposure for similar (though higher resolution) results.  The ZWO CMOS camera can cool to -30C whereas I could only manage -15C with the Atik CCD this considerably reduces thermal noise.

[Macavity]

I suppose it is symptomatic that the main market for Camera Chip manufacturers
is NOT Astronomy? CCD seems far better at eliminating Newton's Rings for Solar
than CMOS. Faint light objects can be less critical of Cameras than bright ones? 

Those who diversify are always happy to hear of (budget) ubiquitous solutions! 

[Adam J]

Hundreds of images are exactly what puts me off this chip as I have a obsy so tracking should not be an issue and I dont want to deal with managing / processing that volume of data. Pretty much decided ill be getting a 8300 if I can ever afford one. Unless someone brings out a mono APS-C chip without the amp glow allowing longer exposures.

[swag72]

For the moment it's still CCD for me..... I have recently bought one, so there's life left in it for me at least! Interesting Atik read...... interesting that the only 2 cons for the CCD were budget and download speed..... nothing actually concrete against the chip and it's use. Nothing that would really be a deciding factor against them to my mind. Yet the cons for the CMOS were much more specific and sensor / technological based. 

 

[RayD]

24 minutes ago, swag72 said:

For the moment it's still CCD for me..... I have recently bought one, so there's life left in it for me at least! Interesting Atik read...... interesting that the only 2 cons for the CCD were budget and download speed..... nothing actually concrete against the chip and it's use. Nothing that would really be a deciding factor against them to my mind. Yet the cons for the CMOS were much more specific and sensor / technological based. 

 

These were my thoughts exactly. However, I'm not going to enter in to the whole CCD vs CMOS debate because, as with everything, what suits some will not suit all. It depends on your imaging desires, style and available equipment.  My preference is for less subs of longer duration, so it's unlikely I shall be making the swap any time soon.

I think there has been several images posted recently from CMOS sensors which are very good indeed but, in my view only, just not quite the level of the very good CCD based ones.  I'm sure this will change as CMOS become more commonplace in DSO AP.

I think the Atik article is very good as they are going to use both, so are probably pretty neutral on the pro's and con's front.

The answer for the OP really is that if the way CMOS captures data suits your requirements, then they are definitely a viable option especially the ASI1600 cool which seems to be producing some very good results.  There is no wrong way on this one, just one which suits you best.

[RichLD]

I've got both - a QHY9m with the KAF8300 and a QHY163m which uses the same Panasonic sensor as the ASI1600MM. I don't do the high gain/lots of subs thing with the QHY163m, instead going for 600s subs at G10/OS70. This configuration gives me subs comparable to 900s subs taken with the QHY9m. Darks calibrate the amp glow out completely.

I'm well happy with mine - I use both cameras on a dual-shooter and love the results I'm getting  

[RichLD]

I'm also not quite sure why the ASI 1600mm seems to get more mention than the QHY163m. It has a shorter flange to sensor distance out of the box in it's favour, however the QHY163m has a heated sensor window and extremely good build quality.

[RayD]

2 minutes ago, RichLD said:

I'm also not quite sure why the ASI 1600mm seems to get more mention than the QHY163m. It has a shorter flange to sensor distance out of the box in it's favour, however the QHY163m has a heated sensor window and extremely good build quality.

I suspect because of the distance you mention, but also the convenience of the USB hub and availability from FLO?

[RichLD]

4 minutes ago, RayD said:

I suspect because of the distance you mention, but also the convenience of the USB hub and availability from FLO?

Yes - perhaps. Modern Astronomy and Rother Valley Optics carry stock of QHY products though - just sayin' 

[Knight of Clear Skies]

41 minutes ago, swag72 said:

For the moment it's still CCD for me..... I have recently bought one, so there's life left in it for me at least! Interesting Atik read...... interesting that the only 2 cons for the CCD were budget and download speed..... nothing actually concrete against the chip and it's use. Nothing that would really be a deciding factor against them to my mind. Yet the cons for the CMOS were much more specific and sensor / technological based. 

I'm fairly sure CCD is the right solution for you Sara (and that you'd get classy results with either approach), but you have a heavy duty mount and more clear nights at your disposal. The advantages of CMOS appear to be more practical than technical, and therefore of more interest to beginner and intermediate imagers. Incidentally, have you ever considered a small pixel camera (CMOS or CCD) to capture more detail in the brightest and most intricate parts of your targets? It might be a good alternative to a longer focal-length scope.

I'm wondering if it's time to rethink the advice given to beginners, there is certainly a case to be made for unguided short-exposure imaging on a lightweight mount as a cost-effective and practical solution with a shorter learning-curve (where possible, I'd prefer to spend time imaging rather than diagnosing issues). I've little experience of guiding but a little hazy cloud scudding through the frame can make it an unhappy experience, and the longer the sub the more imaging time wasted when a bad one comes in.

15 minutes ago, RichLD said:

I'm also not quite sure why the ASI 1600mm seems to get more mention than the QHY163m. It has a shorter flange to sensor distance out of the box in it's favour, however the QHY163m has a heated sensor window and extremely good build quality.

Good point, the 1600MM may simply be better known as it arrived first.

[swag72]

2 minutes ago, Knight of Clear Skies said:

........Incidentally, have you ever considered a small pixel camera (CMOS or CCD) to capture more detail on the brightest and most intricate parts of your targets? It might be a good alternative to a longer focal-length scope........

I have used a couple of Sony chips in the past that have smaller pixels than the KAF8300. In fact I have one waiting to go on the 1200mm frac at the moment  With regards to a longer focal length scope, the 1200mm frac is as long as I will go now, I have played with various permutations of longer focal lengths (RC, SCT and ODK) and I have to say that the fracs suit me more than the other options out there.

[blinky]

44 minutes ago, RichLD said:

I'm also not quite sure why the ASI 1600mm seems to get more mention than the QHY163m. It has a shorter flange to sensor distance out of the box in it's favour, however the QHY163m has a heated sensor window and extremely good build quality.

'cos FLO dot sell 'em and QHY got a bit of a bad name for themselves with the QHY8 and it dewing over (a simple heater band sorts that)

[ollypenrice]

In the context of DSLR versus CCD I've always argued the case for CCD, including for beginners. However, I'm completely open minded on the CMOS question. Over on the French forum there have been some interesting deep sky images taken with very short exposures which, as in planetary imaging, can sometimes 'beat the seeing.'

Knight's arguments and posted M31 are very convincing.

Olly

[blinky]

Would love to see what you could do with one of these Camera's Ollie.  A side by side with a good CCD and your skills would be very interesting

[Ikonnikov]

Being able to use shorter exposures with CMOS does seem to allow some pretty tight images to be produced, there's been some very detailed narrowband Astrobin images of the day taken with these cameras on longer focal length scopes recently. I guess even though the sub lengths used are typically 2-5 minutes (which is far longer than anything that can be called lucky imaging) it still allows you to be a lot more fussy about which ones you throw out compared to with 20 or 30 min CCD subs. The small pixels and high sensitivity also allow for some pretty high sampling rates without too much noise. IMHO, CCD probably still has the edge for lower resolution widefield imaging (especially with the mono chip sizes available) but there isn't much in it. 

 

Paul

[wimvb]

When I retired my noisy DSLR, I considered both cooled CCD and cooled CMOS, OSC and mono versions. Unfortunately, CCD at any given sensor size is considerably more expensive than CMOS. And as the collective knowledge of cooled CMOS increases, the gap in image quality diminishes. Finally, it was results like these that pushed me over to the cooled CMOS side:

http://www.astrobin.com/233878/F/?image_list_page=3&nc=&nce=

http://www.astrobin.com/245464/?image_list_page=2&nc=&nce=

I briefly considered the larger ASI1600/QHY163, but a.) it was over my budget, and b.) I wasn't too keen on stacking hundreds of 32 MB images. (My ASI174 has 4.6 MB/sub.)

Yes, the amp glow looks horrible on single images, but it calibrates out very well. The variable gain of CMOS allows both long exposure and short exposure AP.

I also considered ZWO vs QHY, the QHY camera having a buffer and a window heater. But there are more reports of QHY failing due to driver issues than ZWO.

Mono vs OSC? Again, from studying results from both fields, mono (lrgb) images always seemed to come out "cleaner". And using short exposures of less than one minute, I can rotate through all four filters, capturing maybe 5 images per filter at a time. This makes mono faster than OSC, even if the gap in the clouds seems smaller than my scope's aperture.

Just my €0.02

[Adam J]

8 hours ago, RichLD said:

I've got both - a QHY9m with the KAF8300 and a QHY163m which uses the same Panasonic sensor as the ASI1600MM. I don't do the high gain/lots of subs thing with the QHY163m, instead going for 600s subs at G10/OS70. This configuration gives me subs comparable to 900s subs taken with the QHY9m. Darks calibrate the amp glow out completely.

I'm well happy with mine - I use both cameras on a dual-shooter and love the results I'm getting  

It seems to me that you would know better than most which is producing the best results then. Any comparison images?

One thing I firmly believe though it that all these cameras 8600 and ASI1600 would be easily put to shame by a true mono cooled version of the latest DSLR sensors....heck even the sensor in the very old 6D if mono and cooled would be spectacular. Its annoying to know that the technology is out there just not in mono.

[RichLD]

40 minutes ago, Adam J said:

It seems to me that you would know better than most which is producing the best results then. Any comparison images?

At the moment I don't have any stacked images of the same target with the same processing etc using both cameras, so I've included a single sub from each camera from a recent shoot of NGC7822. The QHY163 sub was 600s, G10/OS70 - the QHY9 sub is 900s. Both used a Baader 7nm ha filter and Nikkor ed180 camera lens at f/3.6.

Both images calibrated with the usual bias. darks and flats. HT was applied in PI. The QHY9 sub was resized to match the QHY163 image in Registar.

QHY163m (CMOS 600s -15C)

 

QHY9 (CCD -20C 900s)

[Adam J]

1 hour ago, RichLD said:

At the moment I don't have any stacked images of the same target with the same processing etc using both cameras, so I've included a single sub from each camera from a recent shoot of NGC7822. The QHY163 sub was 600s, G10/OS70 - the QHY9 sub is 900s. Both used a Baader 7nm ha filter and Nikkor ed180 camera lens at f/3.6.

Both images calibrated with the usual bias. darks and flats. HT was applied in PI. The QHY9 sub was resized to match the QHY163 image in Registar.

QHY163m (CMOS 600s -15C)

 

QHY9 (CCD -20C 900s)

Interesting comparison, I would say that the QHY9m is smoother (but then it has a longer sub length) but that the QHY163m is capturing nicer detail...but that could be because of the pixel size being more suited to the focal length of the lens. Not much in it though.

[RichLD]

28 minutes ago, Adam J said:

Interesting comparison, I would say that the QHY9m is smoother (but then it has a longer sub length) but that the QHY163m is capturing nicer detail...but that could be because of the pixel size being more suited to the focal length of the lens. Not much in it though.

I like them both equally, although it has to be said that the CMOS can be more versatile if required. 

[Thommy]

The CMOS cameras seem very attractive, but my concern is the small pixels producing a pixel resolution that oversamples "by miles", in particular for long focal lengths. I can see their applicability for short FL and wide field imaging, though. CCD's come with larger pixels or you can choose to hardbin your pixels, which is not possible with CMOS. If there would be CMOS available with pixel sizes around 6-9um and extreme sensitivity, I wouldn't hesitate to purchase one.

/Thommy

[wimvb]

28 minutes ago, Thommy said:

The CMOS cameras seem very attractive, but my concern is the small pixels producing a pixel resolution that oversamples "by miles", in particular for long focal lengths. I can see their applicability for short FL and wide field imaging, though. CCD's come with larger pixels or you can choose to hardbin your pixels, which is not possible with CMOS. If there would be CMOS available with pixel sizes around 6-9um and extreme sensitivity, I wouldn't hesitate to purchase one.

/Thommy

Asi174 has 5.86 micrometer pixel and 32k full well. Costs less than 1k£.

Btw, moderate oversampling is good. At 750 mm fl, I find my imaging solution undersampled.

[Knight of Clear Skies]

13 hours ago, RichLD said:

At the moment I don't have any stacked images of the same target with the same processing etc using both cameras, so I've included a single sub from each camera from a recent shoot of NGC7822.

Interesting comparison. Think it shows both are in the same ballpark, although viewing full size I notice there is trailing in the QHY163m shot, which will blur the nebulosity as well.

31 minutes ago, Thommy said:

 CCD's come with larger pixels or you can choose to hardbin your pixels, which is not possible with CMOS.

Hardware binning is important with CCDs due to the relatively high read noise, CMOS images can be binned in post-processing if necessary.