Far too many times in the first hour or so in an imaging session I get excellent stars only to find there is a small dark patch in my subframes caused by dew on the sensor. If I zoom in, it is actually not a darker patch after all – instead it is a few isolated pixels whose values are very different from the neighbor pixels.
This got me wondering whether these pixels can be located and processed away using a PixInsight script. Have anyone thought about this or worked on this? Thanks!!
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IF it’s really affecting only isolated pixels (which is unlikely) and you are aggressively dithering every frame, the stacking filters stand a chance of mitigating the problem. The best way to fix this is to fix the camera. Does it have a broken seal or old desiccant?
John
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I'm under the impression that this is the cost of business of doing AP in Florida summer, but I have not tested other ASI6200MM's. It is a shame because I am getting 1.4" FWHM right now! Here are the dew patch zoomed out and in. They are not really single pixel defects, but a few pixels bounded by dark boundaries.   |
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Are you sure it's dew vs frost? If the latter you can try cooling down your camera more-slowly, and/or replacing the dessicant tablets.
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I used to have a huge dark patch in the center of my 2600mm subs
I just turned on the ASI2600 built-in dew heater in my ASIair app, and the dark spot is gone
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Yuxuan:
Far too many times in the first hour or so in an imaging session I get excellent stars only to find there is a small dark patch in my subframes caused by dew on the sensor. If I zoom in, it is actually not a darker patch after all -- instead it is a few isolated pixels whose values are very different from the neighbor pixels.
This got me wondering whether these pixels can be located and processed away using a PixInsight script. Have anyone thought about this or worked on this? Thanks!! *It is not single pixels (I get them too and I'm not even in FL!) and you cannot process them away unless you dither every subframe by at least 10 px (larger > better). And hope ESD does its job. To be perfectly honest, I may allow 1 or 2 of them in a stack of at least 20 and prune away all the other affected frames to get a decent result.
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I used to have a huge dark patch in the center of my 2600mm subs
I just turned on the ASI2600 built-in dew heater in my ASIair app, and the dark spot is gone Unfortunately for my ASI6200 condensation occurs both on the optical window and on the sensor. Dew heater only takes care of the former.
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Yuxuan:
I used to have a huge dark patch in the center of my 2600mm subs
I just turned on the ASI2600 built-in dew heater in my ASIair app, and the dark spot is gone
Unfortunately for my ASI6200 condensation occurs both on the optical window and on the sensor. Dew heater only takes care of the former. I guess, maybe you need to replace the desiccant tablets then, as others have said
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How cold are you cooling down to? You could probably put this issue to rest if you set a higher temperature when its hot and humid outdoors.
Dark current is under an electron per 5 minutes at 0c. The rate doubles roughly every 6c, so you could go up to +5 or even +10 and probably still not be able to see any adverse effects. If you're already cooling down above 0 then you should probably take a look at the desiccant in the camera and see if you could replace it.
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As a bandaid, you can cool less aggressively, but the only real solution is to replace the desiccant. Processing out a dew donut isn't realistic because you just plainly won't have any signal there.
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Dessicant wont help you there (been there, done that). When it is hot and humid the only way is to keep the temperature above 0 degC.
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Yuxuan:
I'm under the impression that this is the cost of business of doing AP in Florida summer, but I have not tested other ASI6200MM's Hi Yuxuan - I use both the ASI2600 and ASI6200; When it's hot and humid it sometimes takes well over an hour for the dew to clear but it eventually will. The thing to avoid is taking flat frames before it clears because then the flat master will reintroduce it when applied to the good frames.
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