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Old 23-07-2009, 01:22 PM
Hagar (Doug)
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QHY8 Dark Frames.

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.
Attached Thumbnails
Click for full-size image (MasterDark60sec.jpg)
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Click for full-size image (MasterDark120sec.jpg)
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Click for full-size image (MasterDark300sec.jpg)
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Click for full-size image (MasterDark600.jpg)
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Click for full-size image (MasterDark900sec.jpg)
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Click for full-size image (MasterDark1200sec.jpg)
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Click for full-size image (MasterDark1800sec.jpg)
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Last edited by Hagar; 23-07-2009 at 01:35 PM.
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  #2  
Old 23-07-2009, 01:40 PM
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multiweb (Marc)
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Hi Doug, agreed with the fact you don't need to do darks with the QHY8 but any unstretched dark will look like this It's fairer to show a dark stretched
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Old 23-07-2009, 01:54 PM
gbeal
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You guys know where I am with darks, and the QHY8. Why the lighter strip on the left Marc?
Gary
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Old 23-07-2009, 02:04 PM
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Quote:
Originally Posted by gbeal View Post
You guys know where I am with darks, and the QHY8. Why the lighter strip on the left Marc?
Gary
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.
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Old 23-07-2009, 03:26 PM
Hagar (Doug)
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Originally Posted by multiweb View Post
Hi Doug, agreed with the fact you don't need to do darks with the QHY8 but any unstretched dark will look like this It's fairer to show a dark stretched
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.
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Old 23-07-2009, 04:29 PM
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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.
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Old 26-07-2009, 03:23 PM
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Quote:
Originally Posted by Hagar View Post
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.
Here's a dark from a QHY9 at: http://qhyccd.com/ccdbbs/index.php?P...5&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.
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Old 26-07-2009, 03:25 PM
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Quote:
Originally Posted by Gama View Post
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.
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.
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Old 26-07-2009, 03:57 PM
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Quote:
Originally Posted by multiweb View Post
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.
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.

Steve
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Old 26-07-2009, 04:28 PM
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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
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Old 27-07-2009, 05:33 PM
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Quote:
Originally Posted by kinetic View Post
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.

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

Quote:
Originally Posted by Gama View Post
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
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.
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Old 03-08-2009, 12:10 PM
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Doug it seems as though I am now in the qhy8 club, so will be bouncing for clues soon - man i love noiseless images
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Old 03-08-2009, 12:32 PM
Hagar (Doug)
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Quote:
Originally Posted by h0ughy View Post
Doug it seems as though I am now in the qhy8 club, so will be bouncing for clues soon - man i love noiseless images
Congrats David, You wont regret it although like all imaging, at times you might think why.
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Old 03-08-2009, 06:18 PM
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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
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Old 03-08-2009, 06:31 PM
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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.
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Old 03-08-2009, 06:35 PM
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Quote:
Originally Posted by Gama View Post
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.
The 60sec one reveals a similar pattern when stretched.
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Old 03-08-2009, 06:43 PM
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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
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Old 03-08-2009, 06:47 PM
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Quote:
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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
Fortunately it's not my problem--over to Doug.
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Old 03-08-2009, 06:49 PM
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It was referenced to any camera, not just Dougs.

Theo.
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Old 06-09-2009, 06:22 PM
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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.
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