Suggestions please - guide camera selection

[The Thing]

I am now fed up with the noise on my QHY5. The banding is atrocious, but funnily, not consistent. Some nights it works fine and other nights the noise makes star selection well nigh impossible in PHD and I am sure it affects centroid calculations. I do wonder if I got a duff example. Using it with an OAG is frustrating.

I have been looking at the QHY5L-II (mono QE 74%), QHY6, Starlight Xpress CoStar CMOS Autoguider, DMK 21AU04.AS Mono (same chip as my LX/mono modded SPC900!), ZWO ASI 120MM (QE 75%). I sort of favour the QSI as its small, cheap, light and Julian has one.

Any thoughts?

[MarkS]

I sort of favour the QSI as its small, cheap, light and Julian has one.

Which model of QSI?

[Rocket Pooch]

QHY surely?  The QHY6 is the one I have.

[The Thing]

I sort of favour the QSI as its small, cheap, light and Julian has one.

Which model of QSI?

QHY!

[MarkS]

I doubt if you'll see much difference between the QHY5L-II, the ZWO ASI 120MM (which uses the same chip) and the QHY6.

But in my opinion, they all have the same Achilles Heel - the read noise is far too high - 6 electrons or higher.  This is the main limiting factor.

The guiding world is simply crying out for a low noise mono chip with read noise of 1 or 2 electrons - it would allow guiding on stars 3 magnitudes dimmer.  A Sony Exmor sensor for instance?

Such a camera would also make a fabulous high frame rate planetary imager.

Mark

[Mike]

I've always found the Starlight cameras to be excellent. I have the Superstar and it's really sensitive and noise free.

[MarkS]

I've always found the Starlight cameras to be excellent. I have the Superstar and it's really sensitive and noise free.

From the specifications the QHY5L-II has higher QE (75% vs 50%) than the Superstar and lower read noise (6 vs 7-10 electrons) but that is counterbalanced by the Superstar's slightly larger pixel size 4.75microns vs 3.75 microns.  On paper at least, I think you would be hard pushed to see any difference between them.

[RobertM]

Duncan,

If you want to try out my ASI120M you are welcome.  I think you will find it has none of the QHY5 issues.  I must admit I'm surprised you put up with it for so long - the one I had was horrendous and made the Meade DSI look good

Robert

[The Thing]

That's a great offer Robert. Now all I need is a clear windless night - unlike tonight which is clear but blowing a combination of gunpowder, parafin and burnt flesh in our direction

[The Thing]

I have tried out Roberts ASI120MM, I was not impressed.

It didn't pick up any more guidestars that the QHY5 though the image was cleaner. It kept crashing PHD2 (tried it as an ASCOM camera and a WDM camera) and also Sharpcap 2 which has specific customisations for this camera. It wouldn't work over an extension hub (which I always use) or any other hub. Testing inside with the 8mm lens showed a pattern as if horizontal hold on an old TV (for those who remember such things) needed adjusting, this varied with the USB speed setting (available in the WDM driver but not the ASCOM driver). There were no other external USB devices plugged in. I was using the latest drivers from their site.

However Robert said he hadn't really used it and I have also read on-line that ZWO admitted a faulty batch that exhibited some of these symptoms...

[Mike]

Duncan I have a SX Superstar you are welcome to borrow and try out if you like?

[The Thing]

Duncan I have a SX Superstar you are welcome to borrow and try out if you like?

I believe that's an Xbox game, just about right considering the weather!

The CoStar is more in my price bracket (or the Mrs' price bracket to be more accurate).

I am inclined to the QHY5L-II Mono due to its QE 74% vs ~50%, and the fact that there are people investigating serious cooling options for it based on the design of the case which has a thermal pathway block  which is part of the case already on the CCD back.

Or I could go for a QHY6 or even an IMGOH or Brightstar Mammut which is at the top of my budget (there's a used one on fleabay for £299 right now). There are some interesting things on AstroBuySell at the moment as well.

Or do nothing and placate the weather gods

[MarkS]

There are some interesting things on AstroBuySell at the moment as well.

Yes, just got myself a QHY5 for £120

[The Thing]

When your QHY5 comes unscrew the front panel, get the board out (slides) and see if it has a cutaway behind the CCD. If so it's easy to add cooling. Mine doesn't have this "feature" , I don't know if it's early or late models that had this. If it did I would add the cooling and probably be a happy guider as the noise reduction can be substantial, the CMOS warms itself to +28c. Other components generate heat which will show up on really long 300s+ exposures regardless.

[MarkS]

I would add the cooling and probably be a happy guider as the noise reduction can be substantial

Are you sure about that? I find that difficult to believe.  The read noise is at least 5 electrons RMS - probably a lot more.  For the dark current to be noticeable its residual noise would have to approach this read noise and so it would have to generate 5x5 i.e. 25 electrons in the 1-2second guide cam exposure (since 25 accumulated electrons generate 5 electrons RMS of noise).  In comparison, the Canon 350D has a dark current of approx 1 electron at 20C ambient.

I've always thought that read noise was the main limitation of guide cameras.  Happy to be proven wrong!

However, if you're using them for long exposures instead of for guiding then that is a whole new ballgame.