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Old 28-12-2012, 10:19 AM
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BlackWidow (Mardy)
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QHY 8 hot pixel problem

I have had my QHY 8 for a little while now but have not used my scope for about 6 months. I normally image with Bias, flats and lights.

However I have decided to add some darks and remove the bias and create a set of master darks with the bias removed.

Last night I started taking 5 min darks and noticed I had lots of hot pixels in all of my darks that I have not really noticed before. They may have all ways been thier but not noticed on only flats and bias shots, but really evident in blacks.

I would take a guess that I have about 12 - 15 or so and they are the same in all shots so processing with darks will remove them. However is this normal on a QHY 8? or should I increase the TEC voltage to get more cooling? Or will this not change the problem and I should just deal with it.

I have a nice noise free black dark with no noticeable heat problems, only theses hot pixels. I am running the TEC voltage from a 102 controller at around 10 volts.



Any assistance would be great

Mardy
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Old 28-12-2012, 12:09 PM
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Shiraz (Ray)
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hot pixel removal is possibly even better than darks with the QHY8. mine has a handful of relatively hot pix as well - guess it's normal and not a high percentage of 6 million.
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Old 28-12-2012, 02:57 PM
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Hot Pixel removal

Thanks for your help. I have not done the hot pixel map before. What is the process? Do I do it to all my darks, or just to one of the batch. What is the process using this form?

I used it with the standard settings on one dark frame, and it removed all the hot pixels, but made the frame light.


Regards
Martin
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Old 28-12-2012, 06:44 PM
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depends on the software. I use Nebulosity and that can make a bad pixel map in one keystoke using a single dark frame (you can also vary the settings if you want). Once it knows the locations of hot pixels it can then use the bad pixel map in initial processing (prior to deBayer) to replace the bad pixels in all of your light frames. Doesn't change the lights in any other way.

When using bad pixel mapping it is also worth dithering when gathering your data so that any warmer than normal pixels that remain after the hot ones are removed, are spread about when you do the stacking and are not noticeable.

as a personal observation, the QHY8 is standing the test of time rather well - still produces very smooth images and is fairly sensitive as well.

Last edited by Shiraz; 28-12-2012 at 07:03 PM.
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Old 28-12-2012, 08:06 PM
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multiweb (Marc)
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You might get more hot pixels developing with age. The cooler the camera the less I found. A good fresh set of darks will get rid of them or you can make a bad pixel map in nebulosity (easier).
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Old 29-12-2012, 04:27 AM
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Pixel map

Quote:
Originally Posted by Shiraz View Post
depends on the software. I use Nebulosity and that can make a bad pixel map in one keystoke using a single dark frame (you can also vary the settings if you want). Once it knows the locations of hot pixels it can then use the bad pixel map in initial processing (prior to deBayer) to replace the bad pixels in all of your light frames. Doesn't change the lights in any other way.

When using bad pixel mapping it is also worth dithering when gathering your data so that any warmer than normal pixels that remain after the hot ones are removed, are spread about when you do the stacking and are not noticeable.

as a personal observation, the QHY8 is standing the test of time rather well - still produces very smooth images and is fairly sensitive as well.

I also use Nebulosity. So once I have made the bad pixel map at what pont do I add it? When I batch process do I place it instead of darks when adding flats etc? I have tried to look up the process on neb 3 and have not been able to find any details, just the process of creating the pixel maps.



Regards
Mardy
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Old 29-12-2012, 06:07 AM
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when you have saved the bad pixel map, go back to the batch menu and select bad pixel again, this time select "remove bad pixels: BW" and it will ask for the bad pixel map and then ask for the frames to be processed. It will remove the bad pixels and save new processed frames with a badpixel prefix.

Then do what you like with the new frames - remove bias (possibly), deBayer, stack etc - I use the bad pix removal as an alternative to darks - once you have done badpix, I don't think that darks will process properly where the bad pixels used to be.
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