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Qhy8L Light Frames.


redfox1971
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Been having problems with this camera for a long time Bernard had it back to check it out and tested ok been at least 3 months since getting a clear night to test it on the scope,got a chance last night so cooled the camera to -20 and started taken images of the Rosette nebula first couple of images looked promising but then started having problems around the stars as shown in image 2,Any suggestions of what is causing this my offset is set at 117 and gain at 4 lowering gain makes no difference .

post-8423-0-93426200-1452950399_thumb.jp

post-8423-0-10295000-1452950413_thumb.jp

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Taking the two un-debayered images from your drop-box, debayering them and zooming in on the bright stars in the central area plus the dark dust shadow on the right hand side, clearly shows that something in the camera's amplifier is drifting with temperature.

I think you can discount image calibration, if you did calibrate the images in your drop-box, since the same calibration bias, darks and flats would have been used for both early and late light frames in the sequence so both images should be similarly affected. 

The black / coloured pixels that begin to appear around the bright saturated stars suggests that the ADC (Analogue Digital Converter) is not quite set correctly or the anti-blooming gate of the sensor is malfunctioning.

Looking at the pixels around the dark dust shadow shows no change between your early and late image in the sequence, only the bright saturated stars are affected and the only two things I can think of that would cause this is either the ADC offset is drifting as the camera temperature drops, or the sensor anti-blooming gate has a problem, don't think a gain issue would cause the problem but I don't use a QHY so can't be certain.

It might be worth running through the gain and offset calibration again but set the camera temperature to your target temperature first and leave it half an hour to stabilise at that set-point before beginning the gain-offset calibration.

When carrying out the gain and offset calibration do the offset first, make sure the camera port is really covered so that no light can get in, don't do this with the camera on the scope as light will leak in around the focuser draw tube and give you a false offset reading, then adjust the gain with the port open to light but still not on the scope, just point the camera at a brightly lit sheet of plain paper or white painted wall, then go back to the offset adjustment again since the two adjustments mutually interact, adjusting the gain has a small influence on the offset value so you need to run the offset adjustment again following the gain setting, when I used to calibrate medical image sensors I ran through the offset and gain adjustment two or three times in sequence before it was balanced perfectly.

After this, if the fault is still there then it must be assumed the sensor or camera amplifiers have a problem and you would need to contact the supplier for a warranty repair or replacement, try sending the supplier a copy of the comparison image attached below for comment and suggestions, if you bought from Bernard at Modern Astronomy? then he will give you good support to get the problem resolved.

 

Edited by Oddsocks
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Thanks Oddsocks for your detailed help i have been trying once again this evening to set the offset and gain and i am unable to follow the qhy instructions of keeping offset between 500 and 1000 as the rms,max,min values all keep jumping about if i use the values when i first had the camera and select  "ignore over scan area" and do a run of images after every image downloads i get a warning message saying offset to low think i need to find someone with a oscilloscope to test the ccd signal as i see you can adjust the resistance witch is men't to be 2.2v.

Also i always used to get straight lines from my bright stars before this problem.

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Yep, I see it now  -  Almost like loads of dead pixels round the stars.  Sorry, I have no idea whats causing that, I would do as has been suggested, contact Bern again, send him the images and I, sure he will get it sorted.

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i need to find someone with a oscilloscope to test the ccd signal as i see you can adjust the resistance witch is men't to be 2.2v

I guess you are referring back to this thread for the black lines problem: http://stargazerslounge.com/topic/234078-qhy9-mono-camera-horizontal-black-lines/ that was for the "horizontal black lines following a bright star" problem where you adjust the trim pot R27 for 2.2v.

Not sure if the information provided for the QHY9l in the thread would be relevant for the QHY8l, there is not a lot of useful information posted on the web for the 8l.

If the two cameras amplifier boards are the same it could well be a "noisy" r27 preset resistor, they are notorious for becoming unstable with temperature due to oxidation of the carbon film used as the variable resistance.

If your camera is out of warranty and you decide to open it and work on it yourself then, with the power off, mark the current location of the trimmer resistor's shaft with a fine permanent marker pen then gently rotate the resistor shaft from end-to-end a dozen times, this will clean the carbon film, then set the resistor back to the mark you previously made.

If you can not find anyone with a oscilloscope nearby then one of these inexpensive USB oscilloscopes will do: http://www.amazon.co.uk/Hantek-Digital-Storage-Oscilloscope-Portable/dp/B00EDFQ3EU/ref=sr_1_1?ie=UTF8&qid=1453031736&sr=8-1&keywords=usb+oscilloscope#productDetails

They plug into your laptop USB port providing all the normal oscilloscope functions including storage displayed on your laptop screen.

The model linked to is now superseeded but there are still some available from various sources, the replacement model is similar in spec but physically smaller and a little more expensive.

While not as good as a stand alone oscilloscope, they are good for low voltage service work, this one is is good for up to ~30v DC with the supplied probes. For working on voltages above 30v DC with USB oscilloscopes it usually becomes more expensive than using the old stand alone oscilloscopes due to the extra isolation protection needed for the user and the laptop but for working on the camera etc these are fine.

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Hi

Could be hot pixels or dead pixels? In which case they should show up in calibration frames and you'd be able to calibrate them out.

Louise

Yeh, what happens if you take say a 10 minute dark?  Or take a flat frame and have a look, bottom line though, something seems wrong with the camera.

Unfortunately for this type of problem bias and darks would not remove the defective pixels, they are random between exposures and only appear around a bright saturated object.

Bias and darks are taken with the camera shutter closed or telescope/lens capped to exclude light so the defect would not be created, bias and darks, used to remove fixed pattern noise only, would not contain the defect information.

I have read several posts on various forums about unstable readings when trying to adjust the offset and gain on QHY cameras, seems to be a common issue, and wonder why QHY felt it necessary to build this feature into their design, AFAIK no other camera manufacturer does this, preferring instead to set up and program the camera in a controlled factory environment?

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I have read several posts on various forums about unstable readings when trying to adjust the offset and gain on QHY cameras, seems to be a common issue, and wonder why QHY felt it necessary to build this feature into their design, AFAIK no other camera manufacturer does this, preferring instead to set up and program the camera in a controlled factory environment?

I never knew that! Have only ever had the qhy8l ccd and always presumed it was a similar situation for all ccd's.

Louise

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I have put a ticket into qhy so will see what they come up with Bernard at modern astronomy seems to think it may be a dry solder joint causing the problem as when he tested the camera all was fine, He gave me the gain and offset value of 117 offset and 4 gain witch he calculated. Will see what qhy come back with.

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