I'm going to re-shoot my dark libraries. Many poeple suggest that the cover on the 2600 isn't necessarily light proof, so they suggest putting the camera in a black bag to shoot the darks. But I need to cool it to my usual working temperature to match the darks, so won't putting it in a bag interfere with the cooling? I am worried the camera will overheat if I put it in a bag.
What do you do?
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I use the darkness of night. There are plenty of nights I'm not imaging for one reason or another... so they make a perfect opportunity to do a dark library. My rig is assembled in my garage... and my mini PC is connected to my home's wifi. So, I just set my dark sequence to run overnight.
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Stuart Taylor:
I'm going to re-shoot my dark libraries. Many poeple suggest that the cover on the 2600 isn't necessarily light proof, so they suggest putting the camera in a black bag to shoot the darks. But I need to cool it to my usual working temperature to match the darks, so won't putting it in a bag interfere with the cooling? I am worried the camera will overheat if I put it in a bag.
What do you do?
I do it outside so reaching imaging temperature is not a problem. Plus I make sure it is dark and in addition I put a cover over the rig. That is the safest, least hassle way and in my case with many cloudy nights I do not loose imaging time. CS, John
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I put my cooled camera in a dark room under a large box.
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thanks for these suggestions. I also find that when shooting bias frames, I have to insert a long pause in the sequence between each one because the cooler can't keep up otherwise
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I also wouldn't use a bag or box to cover the camera... It will only reflect it's own heat and stress the cooler even more. I leave the camera in the basement (open windows during winter) and capture my darks over night (of course with the camera-cover on as well). I did this with my Asi071, Asi224 and DSP2600 and never encountered any problems 
CS, Marten
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just find somewhere reasonable cool and dark... sometimes installed on rig if its dark but cloudy or indoors overnight.
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I shoot mine in my garage with the lights off. Not covered - just darkish. As it takes 20+ hours to shoot a set these cloudy days are the perfect time. Cheers.
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I have a small fridge in my office. I put the cap on the camera, put it in the fridge, and run the cables out through the door seal to the computer on top. My wife laughs at me, but it works! 😂
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In my unheated garage with the camera under a box.
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I'm not suggesting it doesn't happen to other people, however I've never had any issues with light leaks in my dark frames. I mostly shoot darks with the camera cooled to the desired temperature, in a natural lit room during the day. Never had any issues with my darks.
I'd suggest you try during the day, as normal, and see first if there's a light leak - by stretching the darks, for instance.
If there's no problem, then you don't have to "solve it" beforehand.
CS
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Pedro A. Sampaio:
I'm not suggesting it doesn't happen to other people, however I've never had any issues with light leaks in my dark frames. I mostly shoot darks with the camera cooled to the desired temperature, in a natural lit room during the day. Never had any issues with my darks.
I'd suggest you try during the day, as normal, and see first if there's a light leak - by stretching the darks, for instance.
If there's no problem, then you don't have to "solve it" beforehand.
CS
Thanks. My master dark has these stats (with an offset of 50). Does it look like there is any light leak, would you say? The cap on the ASI2600 looks pretty tight as it's a screw in with an O ring
count (%) 100.00000
count (px) 26091648
mean 500.328
median 500.280
avgDev 1.092
MAD 0.920
minimum 468.100
maximum 23832.271
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Stuart Taylor:
Pedro A. Sampaio:
I'm not suggesting it doesn't happen to other people, however I've never had any issues with light leaks in my dark frames. I mostly shoot darks with the camera cooled to the desired temperature, in a natural lit room during the day. Never had any issues with my darks.
I'd suggest you try during the day, as normal, and see first if there's a light leak - by stretching the darks, for instance.
If there's no problem, then you don't have to "solve it" beforehand.
CS
Thanks. My master dark has these stats (with an offset of 50). Does it look like there is any light leak, would you say? The cap on the ASI2600 looks pretty tight as it's a screw in with an O ring
count (%) 100.00000
count (px) 26091648
mean 500.328
median 500.280
avgDev 1.092
MAD 0.920
minimum 468.100
maximum 23832.271
It's difficult to judge just from the statistics themselves... That being said, although I'm not an expert, I don't think there'se anything wrong with it. You have most of your pixels in the very lower end of the histogram, without being zero (ie clipped). You do have some max/near max pixels, but that again, most cameras have hot pixels that register like that, nohting out of the ordinary in my opinion.
You should try to take a dark frame, and stretch it with PI or PS just enough that the dark pixels are visible, and see if there's anything weird - a proper dark frame stretched shoud be relatively homogeneous, with no bright sides or streaks. If you are unsure, try to upload one so we can check for ourselves.
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Pedro A. Sampaio:
Stuart Taylor:
Pedro A. Sampaio:
I'm not suggesting it doesn't happen to other people, however I've never had any issues with light leaks in my dark frames. I mostly shoot darks with the camera cooled to the desired temperature, in a natural lit room during the day. Never had any issues with my darks.
I'd suggest you try during the day, as normal, and see first if there's a light leak - by stretching the darks, for instance.
If there's no problem, then you don't have to "solve it" beforehand.
CS
Thanks. My master dark has these stats (with an offset of 50). Does it look like there is any light leak, would you say? The cap on the ASI2600 looks pretty tight as it's a screw in with an O ring
count (%) 100.00000
count (px) 26091648
mean 500.328
median 500.280
avgDev 1.092
MAD 0.920
minimum 468.100
maximum 23832.271
It's difficult to judge just from the statistics themselves... That being said, although I'm not an expert, I don't think there'se anything wrong with it. You have most of your pixels in the very lower end of the histogram, without being zero (ie clipped). You do have some max/near max pixels, but that again, most cameras have hot pixels that register like that, nohting out of the ordinary in my opinion.
You should try to take a dark frame, and stretch it with PI or PS just enough that the dark pixels are visible, and see if there's anything weird - a proper dark frame stretched shoud be relatively homogeneous, with no bright sides or streaks. If you are unsure, try to upload one so we can check for ourselves.
Hi. Yes, when stretched my darks look completely uniform grey. Just a scattering of hot pixels but not in any pattern. So I think I am probably good. Thanks
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I usually end up doing darks at the target cooling temperature inside after I go to bed with all the lights switched off inside and remembering to turn off the outside security lights.
FWIW: I'm surprised your ASI2600 16 bit ADC darks have a median of 500 with an offset of 50; that does seem high.
My ASI1600MM pro is only a 12 bit ADC and my darks have a median of about 815 at the same 50 offset (300 sec exposure). Given I have only a 12 bit ADC, I would expect my best median to be 800 with an offset of 50 ( i.e. (50/4096)*65536 = 800 ), so I am happy with my darkness.
I'm probably comparing apples with pears here and actually, at the end of the day, you do have darker darks than I do ;)
One last thought: you didn't say what gain you were operating at. Looking at the numbers you posted, you may be able to reduce the offset as your minimum values are relatively high compared to your median.
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Andy Wray:
I usually end up doing darks at the target cooling temperature inside after I go to bed with all the lights switched off inside and remembering to turn off the outside security lights.
FWIW: I'm surprised your ASI2600 16 bit ADC darks have a median of 500 with an offset of 50; that does seem high.
My ASI1600MM pro is only a 12 bit ADC and my darks have a median of about 815 at the same 50 offset (300 sec exposure). Given I have only a 12 bit ADC, I would expect my best median to be 800 with an offset of 50 ( i.e. (50/4096)*65536 = 800 ), so I am happy with my darkness.
I'm probably comparing apples with pears here and actually, at the end of the day, you do have darker darks than I do ;)
One last thought: you didn't say what gain you were operating at. Looking at the numbers you posted, you may be able to reduce the offset as your minimum values are relatively high compared to your median.
Umm... I'm a bit overwhelmed by this amount of tech, to be honest. I don't think I understand most of it. In any case, my gain is always 105 on the 2600MC pro (for the simple reason that this is the gain just above the big drop in noise on the graph).
The rest of your post baffles me as you seem to be saying my darks are high (500), but then you say I have darker darks than you.
But my understanding of these things is very poor, I'll admit (despite the fact that I have a PhD in a scientific discipline.  )
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IMO, you should not have only 50 (off-set value) as the mean. Remember, darks record read noise and thermal noise, besides some incident radiation (i.e. cosmic rays). If the mean expected value was only 50, it would mean you had 0 read noise, which we know is not the case. I find it highly unlikely that a light leak would turn up to be an homogeneous distribution of light. Most likely, it would result in an asymmetric illumination of the sensor, something akin to Amp glow like we see in other cameras
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Pedro A. Sampaio:
IMO, you should not have only 50 (off-set value) as the mean. Remember, darks record read noise and thermal noise, besides some incident radiation (i.e. cosmic rays). If the mean expected value was only 50, it would mean you had 0 read noise, which we know is not the case. I find it highly unlikely that a light leak would turn up to be an homogeneous distribution of light. Most likely, it would result in an asymmetric illumination of the sensor, something akin to Amp glow like we see in other cameras
I don't understand what you are saying. My mean is not 50. It is 500. (see my post above with the stats)
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Stuart Taylor:
Pedro A. Sampaio:
IMO, you should not have only 50 (off-set value) as the mean. Remember, darks record read noise and thermal noise, besides some incident radiation (i.e. cosmic rays). If the mean expected value was only 50, it would mean you had 0 read noise, which we know is not the case. I find it highly unlikely that a light leak would turn up to be an homogeneous distribution of light. Most likely, it would result in an asymmetric illumination of the sensor, something akin to Amp glow like we see in other cameras
I don't understand what you are saying. My mean is not 50. It is 500. (see my post above with the stats)
Sorry about the confusion. I was actually referring to the comment Andy posted regarding the Mean pixel level being 500 with your offset as 50.
My point is that even with an offset of 50, a mean value of 500 per pixel (out of 65535) isn't high at all, it's quite normal for a proper dark frame. So, in my view, I think you're fine taking darks the way you've been taking them until now, and shouldn't worry about it.
-- MORE IN DEPTH EXPLANATION (or the way I understand it) --
Since we're talking about a 16bit depth camera (ASI2600), that means that each pixel can have a value from 0 to 65535 (or 2^16, that's why it's 16 bit). A value of 0 for a pixel is realy bad for editing, because most image processing software use multiplication and similar operations to "work" on the image. 0 times any number is always 0. So a good way to remedy this is to use an offset, i.e. add 50 or whatever other number you want to ALL pixels, in order to make all 0 level pixels a number higher than 0. Those 0 level pixels can be dead pixels or simply pixels that didn't receive enough photons. In any case, an offset would add to the "mean" value of pixels because it is additive to all pixels of the sensor. 50 for all practical purposes still 99,9% pure black, but since it's different than 0, it's not clipped and can be better used by editing software.
But darks don't capture just the offset. The purpose of dark frames is to capture shot noise, read noise, thermal noise and all noise related to the eletronics of the sensor. That's where a mean value of 500 would come from.
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I use a small ice chest with some cooling packs (hard sided so they can't block the camera vents). I run the power cord and USB cable out and collect away for as long as needed during the day.
As an aside, this discussion was interesting - I found that when I calibrated my Ha data with my last set of darks, most of the signal went with it. Ended up not using darks on that data set - wondering if I need an offset as mentioned above????
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Carl Newberg:
I use a small ice chest with some cooling packs (hard sided so they can't block the camera vents). I run the power cord and USB cable out and collect away for as long as needed during the day.
As an aside, this discussion was interesting - I found that when I calibrated my Ha data with my last set of darks, most of the signal went with it. Ended up not using darks on that data set - wondering if I need an offset as mentioned above????
Did you use a pedestal during the pre-processing? That usuaaly resolves the issue.
Specially with CMOS NB imaging, some pixel values in light frames can be very low, even with a small offset. During calibration, Dark frames (actually the Master Dark) pixel values are subtracted from all light frames in order to remove shot noise from the lights. That means that some values can reach 0, wich is very bad and can greatly degrade the image. Because of this, it is common to use a "pedestal" (something like 100-200) for each light frame pixel before darks are subtracted.
For anyone interested in the subject matter I highly recommended Adam Blocks EXCELLENT video series on the pre processing in pixinsight.
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I have a very large set of darks for both my ZWO AS1294MC PRO and AS1294MM PRO (14 or 12 bit ADC dependent on binning) cameras. That way I can avoid using bias frames at all and have darks to exactly fit most requirements.
They are organized by frame size , BIN, gain , temperature and image brightness (offset value)
I put the covered camera in a large box in our domestic fridge at 4 C - the door is fully light sealed even with the two wires coming out to computer and power supply.
The main hazard is obviously the potential for raids on the fridge by my wife and other family members - so it is important to not only strictly maintain an exclusion zone around the fridge and computer but also to pre-pacify everyone by making sure that essential items like milk etc are left out or it will surely all come to grief :-).
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Pedro A. Sampaio:
Carl Newberg:
I use a small ice chest with some cooling packs (hard sided so they can't block the camera vents). I run the power cord and USB cable out and collect away for as long as needed during the day.
As an aside, this discussion was interesting - I found that when I calibrated my Ha data with my last set of darks, most of the signal went with it. Ended up not using darks on that data set - wondering if I need an offset as mentioned above????
Did you use a pedestal during the pre-processing? That usuaaly resolves the issue.
Specially with CMOS NB imaging, some pixel values in light frames can be very low, even with a small offset. During calibration, Dark frames (actually the Master Dark) pixel values are subtracted from all light frames in order to remove shot noise from the lights. That means that some values can reach 0, wich is very bad and can greatly degrade the image. Because of this, it is common to use a "pedestal" (something like 100-200) for each light frame pixel before darks are subtracted.
For anyone interested in the subject matter I highly recommended Adam Blocks EXCELLENT video series on the pre processing in pixinsight.
Thanks for this. I did watch the Adam Block video in which he very clearly sets out the problem and in in which he illustrates how to manually set a pedestal in the WPB PixInsight process.
It may be worth also noting that the standard 'Calibration' tool in PixInsight also allows you to set an 'auto' pedestal during calibration which is applied if (for example) 0.001% of the total pixels are a negative or zero number. This is the default calibration method I think.
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Thank you for that information. I’m working through Adam’s classes now, I guess I should go back and review some of those. I always avoided the pedestal checkbox as I thought that was what Adam and others recommended.
Thanks again!
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Pedro A. Sampaio:
Stuart Taylor:
Pedro A. Sampaio:
IMO, you should not have only 50 (off-set value) as the mean. Remember, darks record read noise and thermal noise, besides some incident radiation (i.e. cosmic rays). If the mean expected value was only 50, it would mean you had 0 read noise, which we know is not the case. I find it highly unlikely that a light leak would turn up to be an homogeneous distribution of light. Most likely, it would result in an asymmetric illumination of the sensor, something akin to Amp glow like we see in other cameras
I don't understand what you are saying. My mean is not 50. It is 500. (see my post above with the stats)
Sorry about the confusion. I was actually referring to the comment Andy posted regarding the Mean pixel level being 500 with your offset as 50.
My point is that even with an offset of 50, a mean value of 500 per pixel (out of 65535) isn't high at all, it's quite normal for a proper dark frame. So, in my view, I think you're fine taking darks the way you've been taking them until now, and shouldn't worry about it.
-- MORE IN DEPTH EXPLANATION (or the way I understand it) --
Since we're talking about a 16bit depth camera (ASI2600), that means that each pixel can have a value from 0 to 65535 (or 2^16, that's why it's 16 bit). A value of 0 for a pixel is realy bad for editing, because most image processing software use multiplication and similar operations to "work" on the image. 0 times any number is always 0. So a good way to remedy this is to use an offset, i.e. add 50 or whatever other number you want to ALL pixels, in order to make all 0 level pixels a number higher than 0. Those 0 level pixels can be dead pixels or simply pixels that didn't receive enough photons. In any case, an offset would add to the "mean" value of pixels because it is additive to all pixels of the sensor. 50 for all practical purposes still 99,9% pure black, but since it's different than 0, it's not clipped and can be better used by editing software.
But darks don't capture just the offset. The purpose of dark frames is to capture shot noise, read noise, thermal noise and all noise related to the eletronics of the sensor. That's where a mean value of 500 would come from.
Fantastic! Thanks for taking the time to help me with this. I get it now. |
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4.69
7.83
7.91
3.31
2.11
2.10
12.30
3.34
3.61
11.01
