Read noise on CCD cameras... lower or higher is better?

[Gem (Grant)]

Hi all

When comparing cameras... I assume a lower value is better? However, looking at the ATIK range, the more expensive cameras have higher values - which goes against my impression. The new Celestron CCD has 13e- read noise. Is that worse than an ATIK with 3e- or 7e- ??

Any help??

[multiweb (Marc)]

Originally Posted by Gem

Hi all

When comparing cameras... I assume a lower value is better? However, looking at the ATIK range, the more expensive cameras have higher values - which goes against my impression. The new Celestron CCD has 13e- read noise. Is that worse than an ATIK with 3e- or 7e- ??

Any help??

Yes a lower read noise is better. A way to combat read noise is to shoot longer subs. Read noise will only become a problem under darks skies when it becomes more prominent. I don't know about camera specs.

[lepton3 (Ivan)]

You design the electronics to make the read noise as low as practical, but there are always tradeoffs.

One of the biggest tradeoffs is readout time: for larger sensors if you want lower read noise you need slower readout or more expensive ADCs. That is one reason why the more expensive Atik cameras have higher read noise -- they tend to have larger sensors.

-Ivan

[Gem (Grant)]

Thanks!

[CometGuy]

Hi Gem,

I wouldn't necessarily rely on manufacture claims, I'd try and find some independent tests if you can.

There are also other factors you should consider, not just read noise, such as:

1. Quantum Efficiency.
2. Dark current/thermal noise.
3. Size of the sensor.

These come at a premium, particularly point 3.

Terry

[Gem (Grant)]

Ok then.
Quantum efficiency: the higher the better I assume?
Size of sensor: the bigger the better (unless your shooting planets)?

[CometGuy]

Gem,

Yes Quantum Efficiency, the higher the better (keeping in mind colour sensors will always have less).

Larger sensors are sought after for the larger field of view.

If your talking planets, as you say then you field of view is not so important.

What were you intending to use the camera for?

Terry

[Gem (Grant)]

DSO.

I have a webcame on order already for planets. Just got back more tax than I thought, so I am looking around for a DSO camera. No rush at all though. Globs and PN are my favourite objects...

[Tandum (Robin)]

Money talks. How much ya wanna spend

[riklaunim]

Kodak sensors tend to be more noisy than Sony progressive scan CCDs (and cams with Kodak sensors have usually stronger cooling). Also few Sony sensors like interlaced ICX429 found in few astrocams have read out noise at around 15e-

That Celestron camera isn't that perfect as it could be but that read out noise should be a problem with nicely exposed frame The Celestron camera isn't for planetary imaging (slow, big), and it's intended for Hyperstar or EdgeHD + Optec Lepus imaging (+ others). The QE is quite low in this case and such camera IMHO won't be a very hot product There are better / bigger / and even they may be cheaper.

[Gem (Grant)]

Just curious about comparisons and understanding the specs for now. I was picking the Celestron as an example (since I am very happy with my Celestron scope!).
I am probably leaning towards getting something cheap and simple (maybe an ATIK 16ic) to learn the ropes and then use that cheap camera as an autoguider down the track when I get a decent camera. I already have an 80mm refractor that I can piggyback onto the C9.25. It has a 1.25" focuser (Celestron camera is 2" anyway). I got the C9.25 rather than the C11 so that I would have more weight to play with.
Simplicity is the key for me. I spent a while choosing my current scope and ended up with a beauty.
I know the more I spend the better the camera... but I think smaller steps are probably better for now.

[riklaunim]

I use DSI III Pro and recently I also tested Brightstar Mammut Lyuba L429 (similar to DSI II or QHY6 Pro) - two cheap and nice cameras. You can start with something like that.

My C11 setup in DS version:
http://www.nauka.rk.edu.pl/site_medi...ges/setup2.jpg

[gregbradley]

CCD camera specs do seem to be written in another language.

Generally CCD selection has to do with budget, intended type of image and brand specifications. The same chip in 2 different branded cameras can perform quite differently.

With CCD chips you want the highest QE (efficiency of converting a received photon into a charge that can be read, anything 50% or above is good).

You want deep wells (40,000 to 100,000). That means how many electrons can each pixel hold before it is full. All that means really is a low well depth camera will need shorter exposures compared to a deep well camera.

Residual ghost images are something the Kodak full frame chips can suffer from to greater or lesser degree. Not something that would concern you too much but you should know it is a factor. The 09000 chip for example suffers from it a lot. All KAF sensors do. FLI and Apogee have a function that eliminates it. KAI sensors do not have this problem due to the chip architecture.

For camera brands:

1. You maximum cooling ability as the cooling reduces noise.
2. Fast electronics and USB2. Also some electronics are a lot cleaner than others. The same chip can seem very clean say in a FLI or Apogee of Starlight Express camera to name a few I am familiar with but relatively noisy in another.
3. Reliability, cost, accessories available.
4. You really want a buffer on board (the camera has its own memory and buffer with the firmware and drivers on board not in the computer).
5. SBIG cameras have selfguiding which is a very handy thing.

Image buffers, sealed CCD Chambers with inert dry gas to prevent frosting, faster downloads, cleaner electronics are now standard on many camera brands. QSI also has the built in offaxis guider and filter wheel which makes them ahead of many and provides a superior solution to autoguiding than even self guiding (self guiding guides through the filters on a mono chipped camera and Ha requires a 30 second or longer guide exposure which is beyond the guiding accuracy of any mount which requires 1 to 6 second guide exposures on average). SBIG do make a good range of accessories though, especially adaptive optics units.

The KAF8300 chip is hard to beat. QE of 56 to 60% (depending on the camera maker), cheap, very defect free compared to other chips,
low noise.

SBIG St8300 is about US$2000 plus you need a filter wheel or filters. about another $1500 or so.
FLI ML8300 is about US$3495 and probably is the best allround performer but needs filter wheel and filters another $1500 or so.
Apogee U8300 same price - another excellent camera - slow cooling is the only criticism, same as above
Starlight Express not sure of pricing probably similar.
QSI about US$4500 (Optcorp.com or Bintel in Australia) including a filter wheel and a guider so good bang for your buck. The new series 600 has far better cooling and faster downloads making it a hot competitor against the FLI Microline series.
It would be very convenient having it all together in one neat package. Bintel's price is very good and you won't save anything buying from Opt and bringing it in yourself.

Atik, QHY are cheaper entry cameras. Best to ask others about how they perform. I have seen some good images from the QHY9 so it is capable basically they all use the same KAF8300 and its a budget versus features type decision. If US$3500 is out of the question then there they make a good alternative. I think the Atik is around AUD$2500 and it needs a filter wheel and filters which are also cheaper (about AUD$1200-1500?).

New Kodak True Sense colour chipped cameras are no longer low QE.
Colour cameras used to be about 17-24% QE which is really low (45% would have to be about the lowest in monochrome cameras). The new True Sense chips all seem to be around 44% peak QE which is respectable when you consider the monochrome KAI11002's peak QE is 50% and much lower in the deep red area where H alpha emissions from nebula are.

As far as intended use the KAF8300 is a good match for most scopes except long focal length scopes. The pixels are small at 5.4 microns.
This means it suits most refractors and scopes up to about 1300mm focal length at F7. After that it is no longer ideal but will still perform well on nights of good seeing.

I used it on 1260mm at F5 and it worked great. It does not work so well on my large telescope at 2958mm focal length except on good seeing nights and then my other camera walks all over it (KAF16803 FLI Proline).

So for entry imaging a colour version of the KAF8300 isn't bad. You'll lose sensitivity (QE) as that is not a true sense chip (they are all KAI series chips and are fairly new and I have not seen one in use yet but there are several that look really good, like a KAI10100 -10mp one, a KAI8050
8mp one, all the way up to 50mp (low QE on the large chips except the KAF40000 40mp one which is good but only available as a colour chip, not mono).

If you want one shot colour try the new Apogee Ascent or a FLI Microline and order the KAI8050 or KAI10100 chip. That would be interesting to see. I think it would give the mono world a big shake up.

One shot colour has a lot of advantages - no filter wheel and expensive LRGB filters needed with their dust and flex and other stuff to consider (more cables/transformers etc). Every image counts if cloud comes over - you still have a colour image. Mono means you need LRGB (4 images) to capture a colour image. What if you spend 3 hours and cloud comes over before you get the blue filtered image? No colour image, you have to wait until next time.

These new Kodak True Sense chips will give a more viable one shot colour camera and reduce the gap in performance between the 2 types of cameras.

Although they are all small pixelled cameras (5.5micron mostly) so
again they suit shorter focal length scopes below about 1300mm.

I think they probably really shine at about 600mm and F5.

The last time I used my ML8300 on my TEC180 fluorite 1260mm F7 180mm aperture at my dark site with an offaxis guider for guiding giving perfectly round stars it really seemed to hit high gear and was performing superbly. It must have been close to an optimum setup matching the seeing as well really really well.

As far as Sony chips goes, they generally are much smaller and have lower noise and smaller pixels than Kodak. But there is a new one that is 10mp which is interesting. Sony up until now was really the chip of choice for planetary imagers. But with a larger one appearing perhaps they can compete with Kodak better. Kodak make all the way from tiny to 50mp so they have the edge. Sony though seems to make higher performing CCDs but an extremely limited range.

Greg.

[Gem (Grant)]

Thanks for the info! Might take a bit to digest!!