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.

[JohnP]

I use a modified LX webcam (uncooled) - Never had noise probs with guiding...

[The Thing]

I use a modified LX webcam (uncooled) - Never had noise probs with guiding...

I have an SPC900 LX with a mono chip. However it keeps crashing PHD1 - must try it with PHD2! It certainly is sensitive and has a cold finger on the chip to the ali case so a bit less noise on a cold night as well.

[RobertM]

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...

That's interesting, I must admit that I've not noticed any issues with the solar imaging I've done - for instance the video of the plane across the sun was made with that camera.  I will try to repeat your findings when I get it back, let ZWO know and push for a replacement if confirmed.

Thanks for your findings and hope it didn't waste too much of your time !

Addendum: it's nothing to do with the 50Hz flicker of light bulbs/flourescents of whatever is it - just a thought.

Robert

[The Thing]

Hi Robert,

I might have another go outside tonight if the murk clears. I will try a smaller ROI, smallest I tried was something like 640x400, I tried binning x2 and longer exposures/less gain.

The main showstopper for me is that it won't work using a hub,  I have found this stated on the ZWO forum and many other places! I am surprised they make a product which doesn't let you use all its features at USB2 speeds even it that means limiting the features set but I suppose they are in a feature war, it should probably be a USB3 device to get the most out of it.

Meanwhile I am going to stick the SPC900 on the OAG and have a go at Comet Lovejoy about 4am Saturday as it's brighter than ISON and high in the sky at night! Clear skies.

[Carole]

There are a couple of Atik16iC cameras on ABS at the moment for slightly less than a QHY5 and I gather these make good guide cameras, plus it will be a cooled small chip CCD camera to have a go at small object cooled CCD imaging should you so wish (so long as you hang on to your current guide camera and "put up with it" for such occasions).

Not sure if this is of any interest to you.

Carole

[MarkS]

... have a go at Comet Lovejoy about 4am Saturday as it's brighter than ISON and high in the sky at night!

Hardly any difference in brightness now but Lovejoy is much better placed!

[Mike]

Meanwhile I am going to stick the SPC900 on the OAG and have a go at Comet Lovejoy about 4am Saturday as it's brighter than ISON and high in the sky at night! Clear skies.

I was up at around 3am this morning so had a look for it. Found it easily enough with a pair of binoculars in a moonlit sky. It didn't have a long tail and looked more like a globular cluster than a comet but was clearly visible and pretty bright.

[The Thing]

There are a couple of Atik16iC cameras on ABS at the moment for slightly less than a QHY5 and I gather these make good guide cameras, plus it will be a cooled small chip CCD camera to have a go at small object cooled CCD imaging should you so wish (so long as you hang on to your current guide camera and "put up with it" for such occasions).

Not sure if this is of any interest to you.

Carole

Yes, but they are enormous and wouldn't get on the OAG between my big fat scope and the Canon!

[Carole]

Yes, but they are enormous and wouldn't get on the OAG

Ah yes, I had forgotten you were using an OAG.

Carole

[The Thing]

I have been having fun with my QHY5 this afternoon.

Seemingly most of the noise and banding originates from the CMOS and is made worse by the quality of the USB power supply. I considered adding a separate 5v feed to the camera but opted to try something else. I added a 1000uf electrolytic capacitor across pins 1 and 4 of the USB B female socket in the camera to smooth the power supply. There is plenty of room for the component if wires are run to the back of the circuit board. This appears to have cured a lot of the issues!

This was taken with SharpCap2 and is picture of the lightbulbs in the ASI120MM picture below with the same exposure settings. Lens was hand held as the CCD is further back in the QHY5 and couldn't focus with the ZWO to C mount adaptor. There is no banding evident and it looks very clean to me. I have looked at a 10s light excluded image in PHD and that looks good too. Now I need some stars.

[Mike]

That's very interesting and shows the circuit design is very poor if the addition of a component costing less than a penny can greatly improve the output. But then decoupling capacitors are missed out of lots of circuits.

[The Thing]

That's very interesting and shows the circuit design is very poor if the addition of a component costing less than a penny can greatly improve the output. But then decoupling capacitors are missed out of lots of circuits.

I was suprised at the difference it made. Previously I had been disappointed when I wanted to try the camera for planetary images, it was just tooooo noisy, I might give it another go.
I had read that on board power regulators (5v->3v) are underspecified for the needs of the CMOS so this was the only simple thing I could think of that might make the power supply better given that 3 other USB ports will be making varying demands on the hub I use.

[mickw]

Worthy of inclusion in the "technical docs sticky"

Is there a link or is it your design ?

[The Thing]

Worthy of inclusion in the "technical docs sticky"

Is there a link or is it your design ?

My idea, haven't seen anyone else do it. I'll take some piccies - two bits of wire and a capacitor woarrr! But wait until I've tested it on stars before you get too excited!

[mickw]

My idea, haven't seen anyone else do it.

[RobertM]

Well worked out Duncan, just goes to show what a bit of determination can do !

Mick, you worshiping beer again

[The Thing]

Well, the QHY5 definitely performed better, there was very little banding in PHD2 when I had a star or two in the FoV and only a little fuzziness. I'm happy but it's still not sensitive enough for use with an OAG at f6 or f10 and be certain of getting a usable star.

Meanwhile I found this very interesting comparison of a Lodestar vs a QHY5L-II on Cloudy Nights. I think a QHY with my name on it might be finding it's way into Santa's sack (I'm sure the postmans' called Santa).

[MarkH]

Horizontal adjustment  yeas I remember that

[The Thing]

I am now the owner of a QHY5L-II Mono. Happy Christmas to me!

[Mike]

Yay! \o/

Just in time for DSC too!

[JohnP]

Nice one Dunc. It'll be interesting to do your same bedroom test.... Did you get it from Bernd...? John.

[The Thing]

Yes, I got it from Bern. He did a deal on the Deluxe kit which was nice. I tried it out on the laptop and and could get ~250fps at the lowest res 320 x 240 directly connected to the USB3 port. I used that one as there is nothing else connected to its controller.

I can't repeat the test as the lens with Robert's ASI120MM is very different to the 8mm f1 supplied with this kit, I get a much wider FoV. The kit also has a 1.2mm 180 degree f2 lens for all sky imaging and I would really like to try it out. The Deluxe kit contents all seems very good quality and I would be hard pressed to source the lenses for the price let alone the tripod mount etc. The tin it come in is another matter!

Now I've got to see how the camera goes in the OAG EP fitting - no T-threads.

[JohnP]

cool - so I am guessing it would make quite a nice planetary imaging camera as well..

[Mike]

Great! With the all sky lens you could get live video of meteor showers too.

[Rocket Pooch]

cool - so I am guessing it would make quite a nice planetary imaging camera as well..

It should do but I don't know how many times people talk about FPS when the exposure is say 1/100th second or down to 1/30th which means you can't get 150fps.

No doubt somone wil now talk about noise.

But this camera looks great.

[The Thing]

The new guide cam was excellent, it took a full lump of cloud to lose a guide star in PHD.

PHD had trouble recognising the blobs the old QHY5 presented amongst the noise as stars and quite often started following a bit of static instead of a star as soon as a bit of murk went across the FoV.

One downside is the much smaller chip so there is a smaller patch of sky to find a star in. The QHY5 showed about 20% of the view of the DSLR even through an OAG! The QHY5II-L shows about 8% at a guess.

Also mounting the camera in the Brightstar OAG isn't the best bit of engineering. Firstly you need an eyepiece extension tube to reach focus. I used a Barlow with the lens cell removed. The QHY5 was screwed on with a T-Mount extension. The QHY5II-L is therefore not so solid and I am going to have to get a CS mount male to T-mount female adaptor to remedy this.

Focusing the camera is difficult due to the engineering of the Brightstar unit. I am exploring helical focusers and will probably modify an old lens (rip all the innards out and glue on T fittings) to do this which will also solve the eyepiece extension problem.

I did a few vids of Jupiter at about 50fps and it looks promising as a planetary camera. Images to follow on an appropriate thread!

[JohnP]

cool - yes the brightstar has a real crap focus mechanism....

[Rocket Pooch]

I focus mine in the daytime makes it 100% easier to do.

[The Thing]

Did that on the distant pylons in the north east gap between the trees at Blacklands. The knurled screws don't hold very well and the sliding action of the camera holder is pants. On top of that the fine focus rotating bit is very rough. I even put a dab of boron grease on it but it made no difference as the thread is compromised by the locking screw tightening on it. Clever engineering not. Maybe I got a Friday model . I previously have had to detach the prism and re-glue it as it was wonkily sitting on a blob of glue in one corner. I would spend more next time.

[JohnP]

Dunc - I don't even bother fine focussing mine - as long as its close. My guide stars are like distorted crescent moons & the guide software still finds the centroid.. Also, my filters all focus at different places anyway & there is no way I am changing the focus of the Brightstar OAG in middle of a cold night if I change to a different filter...

[The Thing]

The better focused it is the more stars I will be able to choose from and the less susceptible to being lost in Beckenham where the sky seems to vary in transparency by the minute some nights. I suspect that the takeoff prism is well into the vignette despite being extended in as far as it will go and that the amount of light available is limited by the fact that its an SCT even if it is at f6.3. I don't have filters to worry about and surely they are behind the OAG or you will be guiding in each colour or Ha!

[Mike]

It is advisable to have slightly out of focus stars for guiding as it makes it easier for the software to find the centroid.

[JohnP]

 

and surely they are behind the OAG or you will be guiding in each colour or Ha!

Obviously, but like I said my filters are not par focal so when I change focus for a particular filter it changes focus for the OAG. I have a refractor so both filters and oag are on focus tube...

[The Thing]

It is advisable to have slightly out of focus stars for guiding as it makes it easier for the software to find the centroid.

Yeah but you have to have stars showing up and I seem to pick targets where they start at mag 10 and less! If they are not pretty well focused they don't show up. They will always be a bit fuzzy due to the Meade high edge optical quality