ASI1600MM COOL PRO SENSOR ANALYSIS

mAnKiNd
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ASI1600MM COOL PRO SENSOR ANALYSIS

Post by mAnKiNd » Thu Jun 21, 2018 2:56 pm

Just got my new camera last night and the clouds rolled in with rain - of course they did...so did a sensor analysis at -10°C and -15°C with brightness (offset right?) set to 10...seems there is a slight drop in read noise & DR when cooler..shot through an Astrodon gen 2 Luminance filter using an A3 tracing light box at minimum settings through a single layer of white t-shirt.
ASI1600MM COOL PRO SENSOR ANALYSIS.png
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Cheers
Minos

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Re: ASI1600MM COOL PRO SENSOR ANALYSIS

Post by oopfan » Thu Jun 21, 2018 6:04 pm

Hi Minos,

This is a very interesting topic since I am interested in purchasing a cooled camera.

My understanding is that the most significant benefit of cooling the sensor is by reducing dark current. Several months ago Robin shared with me a method for calculating it. I created a spreadsheet (see attachment). In the attached screenshot, the input fields are highlighted in yellow.

Begin by covering your objective just as if you were taking dark frames. Choose a gain and offset. perhaps gain 100 and offset 20. Select the FITS output file format. Capture 10 frames at 30-seconds exposure. Capture 10 frames at 60-seconds exposure. Capture 10 frames at 90-seconds exposure. Capture 10 frames at 120-seconds exposure. Open each FITS file one-by-one and fill in the yellow-highlighted matrix with the Mean ADU value from the statistics section of FITS Liberator. Finally fill in the "e/ADU" value associated with your gain. The dark current is the value in the cell labeled "e-/pixel/s".

I would be thrilled to know your camera's dark current. For some reason manufacturers and retailers fail to publish this number. Often times they simply say "TBD".

Thanks,
Brian
Attachments
Dark Current.xlsx
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SharpCap Method screenshot.jpg
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Re: ASI1600MM COOL PRO SENSOR ANALYSIS

Post by admin » Thu Jun 21, 2018 7:28 pm

Hi,

yes, read noise is practically unchanged by cooling. Thermal noise is reduced significantly (and this is the main point of cooling). If you have fixed pattern noise or amp glow it may or may not be reduced, depending on the exact cause. If it does reduce it typically doesn't go down as much as the thermal noise.

cheers,

Robin

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Re: ASI1600MM COOL PRO SENSOR ANALYSIS

Post by mAnKiNd » Fri Jun 22, 2018 10:50 pm

Hi guys,

Yes, the reduction in read noise and DR that I observed from higher cooling is probably statistically insignificant if enough repetitions where conducted and the results compared with a students t-test.

Brian, you are correct in your understanding that cooling mostly helps with reducing dark current, this has always been my understanding as well.

I'll surely give the method you outlined above from Robin's suggestions a go and share my findings. What temperatures would you be interested in repeating this test at? Say 10°C vs -10°C?

Cheers
Minos

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Re: ASI1600MM COOL PRO SENSOR ANALYSIS

Post by oopfan » Sat Jun 23, 2018 1:54 am

Hi Minos,

That is a lot of work for you to do +10C and -10C. It would be fascinating to see the difference but I would be happy to see the results for just -10C so that I could compare it to my uncooled camera's dark current at +68F.

Thanks,
Brian

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Re: ASI1600MM COOL PRO SENSOR ANALYSIS

Post by mAnKiNd » Sat Jun 23, 2018 2:16 am

Hi Brian,

No biggie buddy, testing is currently underway. Will indeed be fascinating to see the comparison as you say.

Will report back shortly with results :)

Cheers
Minos

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Re: ASI1600MM COOL PRO SENSOR ANALYSIS

Post by oopfan » Sat Jun 23, 2018 3:22 pm

Minos,

I see that you also have the EFWMini. I love mine. I've got mine loaded with LRGB plus a "Dark" filter - one less trip outdoors to put the lens cap on!

I am guessing that your "HO" stands for Ha and OIII?

I am thinking about buying the 8-filter EFW and then loading it with LRGBSHO plus "Dark".

So then I'll load my EFWMini with Photometric filters plus "Dark".

Brian

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Re: ASI1600MM COOL PRO SENSOR ANALYSIS

Post by mAnKiNd » Sat Jun 23, 2018 5:11 pm

Hi Brian,

I used a dark filter in my QHY wheel since last September, but gave up on the idea because of light leaks with that wheel. Sold them now and got this setup, maybe the efwmini is better sealed. You can check this by sitting with the scope inside at night but with bright lights on next to it, then take some darks and then switch the lights off for darkness, take some more darks and then compare the exposures. With the qhy wheel, I found there was significant light leak, i certainly couldn't shoot darks indoors unless i was in total darkness and since my "backyard" is riddled with LED's from the surroundings, I gave up on the idea. I haven't tried the efwmini yet, it honestly looks and feels better built in my hand and perhaps seals better. Either way, I chose to go back to covering the scope for darks, because i figured if there's light leaks anyway with these wheels, I might as well use that slot for a transmission filter!

HO is Hydrogen+Oxygen, yes!

8-wheel sounds great loaded with those and then have you're efwmini with photometrics! One day, I might dive into those as well and experiment with them.. . How would you go about changing wheels on the same camera, simply screw-unscrew? Would be nice to hve a snapon/off mechanism to switch easily between wheels, something akin to changing Canon lenses ;)

Last night I acquired darks at 10x30s, 10x60s, 10x90s, 10x120s and repeated at 20°C, 10°C, 0°C, -10°C & -20°C. I have all the raw data and I'm trying to upload it to a shared drive folder (~6GB of data) to share here, but internet is being frustratingly slow...so please bear with me. I'll plug the numbers into the spreadsheet you provided me though, first chance I get and then I can share the graphs.

Cheers
Minos

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Re: ASI1600MM COOL PRO SENSOR ANALYSIS

Post by mAnKiNd » Sat Jun 23, 2018 11:06 pm

Hi Brian,

Here's the link to all the RAW data I captured last night:

https://1drv.ms/f/s!Ao72jgSanTqfur8DtA0-9E_SIjJBNg

I'm also sharing this openly with all who may be interested in such data.

Just for clarification, here are the captures again:

Dark frames captured at:
10x30s
10x60s
10x90s
10x120s

with a brightness (offset) of 20 and a gain of 100

All exposures above repeated at:
20°C
10°C
0°C
-10°C
-20°C

I modified the 'Dark Current' spreadsheet you shared before to include all the temperature ranges I recorded at.

I won't have time right now to plug in the numbers into excel due to certain "other" constraints at the moment, so please feel free to go ahead with that. Let's collaborate on this one and looking forward to seeing the results!

Cheers :)
Minos

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Re: ASI1600MM COOL PRO SENSOR ANALYSIS

Post by oopfan » Sun Jun 24, 2018 12:33 am

Minos,

Preliminary results:

At 0C your dark current is one-tenth of mine at +68F !

By the way, in your SC settings do you have this option checked: "Save 10/12/14 bit images in FITS files without stretching to 16-bits)" ? I ask because your hot pixels are coming in at 4095 instead of 65535.

I am responsible for requesting that option. What I do is this: I check the box when I do Photometry but I uncheck it for Astrophotography.

Brian

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