QHY8 Dark Frames.

[Hagar]

In recent weeks I have had quite a number of emails regarding the QHY8 Cooled CCD camera.

Thinking about which way to reply I decided the best initial test that could be carried out was that of displaying the dark noise generated by this camera. I set about creating a set of Master dark files and have attached them below. They have been quite heavily stretched to show up any defects and I will leave the results to you.
The files are displayed in order: 60sec, 120sec,300sec, 600sec, 900sec, 1200sec and 1800sec.

Summing up my responses. My real conclusion about the questions asked is " I would buy one again in a heartbeat. I believe it is the best bang for your buck available in the Astro imaging market today."

These are my thoughts and I have no connection in any way with QHY or their cameras appart from owning one.

[multiweb]

Hi Doug, agreed with the fact you don't need to do darks with the QHY8 but any unstretched dark will look like this :whistle: It's fairer to show a dark stretched ;)

[gbeal]

You guys know where I am with darks, and the QHY8. Why the lighter strip on the left Marc?
Gary

[multiweb]

They all got it, even the QHY9, QHY11. Something to do with the hardware. Not sure what it is. The difference between the right and the left is less than 20 ADU though, so we're splitting hairs still.

[Hagar]

I think you may need to have your camera looked at Marc, The darks from mine are nice and even. You wouldn't be using a plastic lens cap would you? These are quite see through for IR light transmissions.

This is a 30minute Dark taken with full cooling.

[Gama]

Yeah, looks like stray light comming in somewhere.
You should do darks in the dark just in case of light leaks. But as many said, darks are not needed, but if you like doing them, go for it.

Theo.

[multiweb]

Here's a dark from a QHY9 at: http://qhyccd.com/ccdbbs/index.php?PHPSESSID=f9eb2c98324db4e 840bbacd04fe3ab05&topic=1070.0
taken bu Quy a while ago. Can you post or email one of your darks in FITS? I'll check it out. Thanks.

[multiweb]

As said it is stretched to the max. One side may be 1000ADU and the other side would be 1020ADU or so. Light leaks gradients show a much bigger difference in ADU on any gradient.

[kinetic]

It could be amp glow showing? A downfall with modded webcams
with a lower dynamic range. Not sure if the QHY8 would suffer from
this.
One way to prove that would be to do a similar stretch on a 'light'
frame.:shrug:

Steve

[Gama]

The QHY-8 does have Amp glow, but has the ability to disable it in the setup when you connect to it. I always have it set to ON.


Marc, you may want to ask Qiu what he thinks about your issue, maybe software or similar..

Theo

[multiweb]

No there's no Amp Glow problem with the QHY8. As Theo pointed out you can switch this on/off in the capture software.


Ok, I think everybody's getting confused here. Nothing's wrong with the camera or the software used. The dark I posted is a stack of 40 x 0.8s. Call it a bias if you want. The ADU level on the bright part of the frame and the top is approx 1044, the darker parts are 1021 ADU. So the image is scaled as a 16 bit TIFF file from the raw FITS file with a range of 23 ADU which is minuscule. If I load Doug's dark frame and measure it (although converted from JPEG to TIFF) they show a range of approx 240ADU between the darkest pixel and the lightest.

My point was that scaling a picture can make it look like anything you want. No more no less. ;)

[h0ughy]

Doug it seems as though I am now in the qhy8 club, so will be bouncing for clues soon - man i love noiseless images

[Hagar]

Congrats David, You wont regret it although like all imaging, at times you might think why.

[Geoff45]

Actually, more is revealed with a stronger stretch. Here are two stretches of Doug's 1800 sec dark,the first with ccdstack and the second with maxim. The good point is that there is no trace of defective columns, which is quite unusual. It's also hard to know how much of this is genuine data and how much is due to stretching a compressed jpg, which I imagine will introduce some artifacts. You'd really have to go back to the original files I guess.
Marc's point that scaling a picture can make it look like anything you want is a good one.
Geoff

[Gama]

These look like light leaks. Its not a normal dark. At 30 minutes exposure, you really need to make sure the camera is really covered properly.

Theo.

[Geoff45]

The 60sec one reveals a similar pattern when stretched.

[Gama]

You still need to make sure it is sealed 100%. You need to remember any ccd camera, is so sensitive to pick up a galaxy's light and show up on a ccd, needs to make sure it is absolutly dark.

You should try and rotate the camera or place it in a different spot and try the dark again.

Theo

[Geoff45]

Fortunately it's not my problem--over to Doug.

[Gama]

It was referenced to any camera, not just Dougs.

Theo.

[sadia]

hmmm i am getting a bit confused here! Marc is saying its usual for QHYs, where others are saying there might be some issue with the CCD or there is a possible light leak.

My dark shows the same pattern. So i thought may be light leak and let me try bias because surely bias cant have light leak. I was wrong same issue (see attached). Then i tried quite a few things like placing the ccd in total dark, changing angle, changing cap...etc etc but its always the same pattern.

So is there an issue I mean does your QHY8 behave the same way? I thought i would just clarify my doubt in the forum first.

[Hagar]

I think this whole thread has gone way beyond the normal with regard to dark framed images. The original post of dark frames was in fact just to point out the small amount of hot pixels which are present in a NORMAL and I mean NORMAL Dark frame. Not a frame that has been stretched until all pixels are displayed as white, well almost all. If we were to take each pixel on a scale with reality in mind we would find the diference in the ADU/e count to be very similar.

Marc made a very valid point when stating that it is possible to make a dark look like whatever we want and to stretch a dark to the extent as indicated above is way beyond what would be considered normal or constructive.

The reality is that I doubt any camera on the market could stand the amount of stretching displayed here and perform anywhere near as good. The Sony CCD in the QHY8 has dark currents well below almost all Kodak CCD used in Astro cameras and without doubt less bright pixels than the Kodak range.

What must be remembered in all this is that some have higher sensitivity, some lower dark noise and some better single colour response. The choise is a personal one and one based on your own requirements.

I posted the darks purely to show prospective purchasers what they can expect from the QHY8 camera with respect to dark noise. I have been asked this question on numerous occasions by PM and email and my response has always been the same." In most cases there is no real need for dark frames but if you want a very small lift in image quality and I mean very small then it is worth making a library of darks and using them."
I have such a library and use it in most cases but don't for some where bias frames are enough.

I hope this post explains what was meant by thread and helps someone make up their mind on a great camera which can produce some great results. Don't expect miracles with any camera, even the most expensive can produce junk. Imaging is a matter of a lot of influences and not just the camera, focus, processing, exposure time, registration and collating and things like seeing conditions all add up to final image quality.

Good luck with your imaging Guy's, Have fun.

[marki]

Have to agree with Doug here. The camera generates very little dark current, so little in fact I often don't bother with dark frames (flats yes due to dirty glass :D). Marc I have never had a dark frame look like that in nearly two years of owning a QHY8. Perhaps you streched it so much it ripped in two :P.

Mark

[multiweb]

:lol: This thread is till going? :lol: If you do flat fielding you do need to shoot bias to scale them correctly. So if you looked into your bias levels and inspect them you would see similar patterns. :thumbsup:

[gregbradley]

The original dark posted looked pretty fine to me.

Here is one from my FLI ML8300 at -40C 600 seconds. Not much noise but there is a pattern noise. The Kodak 8300 chip seems to be a real winner and more and more great images are coming from them in various manufacturer's cameras. Kodak really got it right with this one.

Little bit of amp glow top left otherwise very very clean and perfect. You won't see darks this perfect from many chips.

[Gama]

Greg's correct, Kodak really pulled their socks up on this new sensor.
But all the newer CCD's from Kodak are performing better than the first gen, but thats to be expected, technology moves in one direction.
Even in warmer temps, the Kodak sensors being pumped out seem to have better dark signal.


Theo

[Prickly]

Hi Doug,

Good luck with the new ccd. The QHY8 certainly is a very nice ccd and hard to beat for the size and price in my view (no affiliations here either). I have had the chance to use one on my scope once and it really was great.

Hard to tell how stretched some of those images are and what this means in a practical sense - from my recollection with Kens QHY8 there was very little noise apparent in the images we obtained and I gather Ken rarely bothered with darks. Proof of the pudding is in the eating - look forward to seeing some nice shots.

Clear skies and happy shooting.
David