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Dark noise ZWO ASI174MC or ASI174MM, ASI120MC or ASI120MM

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#1 Vars191

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Posted 01 June 2015 - 09:22 AM

Hi All
Has anybody use a ZWO ASI174MC or ASI174MM camera if you do what is the dark noise like, the spec of the sensor used it should be a kick ars camera especially compared to the ZWO ASI120MC or ASI120MM  all things being equal
Please could someone do a comparison
Thank you



#2 gregj888

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Posted 01 June 2015 - 04:02 PM

I got a few dark frames from the ZWO ASI120MM that shows 0 adu counts for most of the frame on 60 second darks.

 

A review of the data sheet shows that sensor has built in black level correction, row wise noise correction and column correction.  These can be disabled on the chip BTW, I don't know if the camera allows disabling. Anyway, this makes any statement about dark noise difficult or impossible using dark frames only.  From the description the actual values subtracted also change... depending on what you are doing, this could be bad.

 

An initial test of a borrowed QHY5Lii showed very good SNR (tested with a referenced source).  This uses the same Aptina sensor as the ZWO ASI120MM.  I just received a QHY5Lii I'll test more completely.  Not the ZWO, but may shed some light on things.  The only way I know to test a camera with Digital Noise Reduction is with a calibrated source and look at SNR and/or absolute magnitude (if noise goes to 0, SNR looks good even with little signal).  This test should be done near the noise floor (minimal signal), IMHO.

 

I don't have a data sheet for the ASI174 or the IMX174 sensor, but maybe you can find one.

 

Just a heads up...



#3 Vars191

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Posted 01 June 2015 - 06:02 PM

I got a few dark frames from the ZWO ASI120MM that shows 0 adu counts for most of the frame on 60 second darks.

 

A review of the data sheet shows that sensor has built in black level correction, row wise noise correction and column correction.  These can be disabled on the chip BTW, I don't know if the camera allows disabling. Anyway, this makes any statement about dark noise difficult or impossible using dark frames only.  From the description the actual values subtracted also change... depending on what you are doing, this could be bad.

 

An initial test of a borrowed QHY5Lii showed very good SNR (tested with a referenced source).  This uses the same Aptina sensor as the ZWO ASI120MM.  I just received a QHY5Lii I'll test more completely.  Not the ZWO, but may shed some light on things.  The only way I know to test a camera with Digital Noise Reduction is with a calibrated source and look at SNR and/or absolute magnitude (if noise goes to 0, SNR looks good even with little signal).  This test should be done near the noise floor (minimal signal), IMHO.

 

I don't have a data sheet for the ASI174 or the IMX174 sensor, but maybe you can find one.

 

Just a heads up...

I have not been able to find a full specifications on the sensor IMX174 but I have seen photos of dark frames on the ZWO ASI120MC with different time exposures and ambient temp - not good


Edited by Vars191, 01 June 2015 - 06:08 PM.


#4 rice224534

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Posted 02 June 2015 - 06:18 AM

Hello,

 

These are dark noise pictures from my ZWO ASI174MM. The 16bit integer fits files (1936x1216pixels) for my ASI174MM are captured by FireCapture. The dark noise in the fits files are displayed in the range of 0 to 10000. For 0.1sec exposure, I also show the picutre of 0 to 2500 range due to low dark noise. Apparently, my camera has positive amplifire glow (maybe) at the lower left.

 

Koji

 

Capture conditions:

ZWO ASI174MM

FireCapture v2.7.08beta

Gain 400

Gamma 100

Ambient/Camera temperature: 41 degC

Exposures: 0.1sec, 1sec, 5sec, 10sec

Attached Thumbnails

  • asi174mm_darknoise_exp00.1s_range0to02500.jpg
  • asi174mm_darknoise_exp00.1s_range0to10000.jpg
  • asi174mm_darknoise_exp01.0s_range0to10000.jpg
  • asi174mm_darknoise_exp05.0s_range0to10000.jpg
  • asi174mm_darknoise_exp10.0s_range0to10000.jpg

Edited by rice224534, 02 June 2015 - 07:38 AM.


#5 astronomy25

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Posted 02 June 2015 - 06:58 AM

these pictures were make with ASI 120mm and Taka fsq 85mm;

 

They haven't been subtracted dark frame

 

 

 

get.jpg

 

get.jpg


Edited by astronomy25, 02 June 2015 - 07:00 AM.


#6 Vars191

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Posted 02 June 2015 - 02:34 PM

Hi All
I was after a few Dark Frame with settings from ZWO ASI120MC and ASI120MM and ASI174MC and ASI174MM so I could make a comparison so I can select the best Camera for me to get, I have had a lot of advice on which one to get but nothing is standing out as the BEST at this stage to use with a 8"SCT for PLANETERY and DSO objects
Please help me
Thank you all



#7 Vars191

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Posted 02 June 2015 - 03:06 PM

ASI 120MM at 22 degrees C and 17 second exposure

 

ASI 120MC at 19.3 degrees C and 17 second exposure

Attached Thumbnails

  • 1.jpg
  • 2.jpg

Edited by Vars191, 02 June 2015 - 03:17 PM.


#8 Peter in Reno

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Posted 02 June 2015 - 03:17 PM

For one size fits all setup, I would get ASI174MC/MM. For planetary, you can use ROI so it should work well for planetary imaging. For DSO, you can use the full resolution but be aware that there's no cooling in ASI cameras. Cooling is very beneficial for not only to decrease dark signal but also reliable calibration with darks, bias and flats. Make sure you do heavy dithering during long sub-exposure imaging for ASI174 to remove unwanted noise like dark signals and FPN (fix pattern noise).

 

For fair comparison in dark images between two cameras, make sure you use the same non-linear stretch for both images. For example, use the same stretch for the mono version onto color version and vice versa.

 

Peter


Edited by Peter in Reno, 02 June 2015 - 03:27 PM.


#9 Vars191

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Posted 02 June 2015 - 03:27 PM

For one size fits all setup, I would get ASI174MC/MM. For planetary, you can use ROI so it should work well for planetary imaging. For DSO, you can use the full resolution but be aware that there's no cooling in ASI cameras. Cooling is very beneficial for not only to decrease dark signal but also reliable calibration with darks, bias and flats. Make sure you do heavy dithering for ASI174 to remove unwanted noise like dark signals and FPN (fix pattern noise).

 

For fair comparison in dark images between two cameras, make sure you use the same non-linear stretch for both images. For example, use the same stretch for the mono version onto color version and vice versa.

 

Peter

 

I think you are right I will have to wait till the ASI174MC comes out (when ever that will be) the noise on the ASI120MC is very bad


Edited by Vars191, 02 June 2015 - 03:35 PM.


#10 Peter in Reno

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Posted 02 June 2015 - 04:08 PM

Which noise are you referring for ASI120MC? Is it more pronounced from longer sub-exposure times? I hope these are not shown during fast frame rate (> 30FPS) or very short exposures.

 

I have not seen any reports for ASI174 cameras saying it has significantly less noise than ASI120 cameras. I know that ASI web site stated no FPN in ASI174 but I would like independent review first.

 

http://astronomy-ima...MM_Features.pdf

 

Peter



#11 Vars191

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Posted 02 June 2015 - 04:21 PM

Which noise are you referring for ASI120MC? Is it more pronounced from longer sub-exposure times? I hope these are not shown during fast frame rate (> 30FPS) or very short exposures.

 

I have not seen any reports for ASI174 cameras saying it has significantly less noise than ASI120 cameras. I know that ASI web site stated no FPN in ASI174 but I would like independent review first.

 

http://astronomy-ima...MM_Features.pdf

 

Peter

http://notesfromasma...sure-noise.html



#12 Peter in Reno

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Posted 02 June 2015 - 04:51 PM

I am not sure if the write-up is accurate. First of all, I believe to accurately compare dark frames is to take RAW images (before deBayer) from color camera and also make sure the stretch of both images are equal. I doubt the stretch of both dark images from the blog are equal.

 

It is normal for color cameras to appear less sensitive because of Bayer Matrix filters overlayed over the CMOS sensor. It's no different than having R, G, & B filters mounted over the monochrome cameras. Both mono and color sensors have SAME sensitivity BEFORE the filters. It's also normal for color images appear to be noisy due to Bayer Matrix filter arrays but it does not mean it's noisy. It's just the way color sensors are made.

 

I have seen good number of fantastic pictures of planets taken with ASI120MC color cameras and I could not tell whether it was from mono or color camera.

 

Bottom line, I would dis-regard this blog because I do not think it's accurate.

 

I do agree that mono camera with filters can produce better results but I am not sure for planets like Mars, Jupiter or Saturn because the sub-exposure times are very short, frame rate is high and all three planets are very bright. This is especially true for moon and sun. The advantage of mono camera is you can use any filters you want for solar, lunar and planets and you have more control than color cameras.

 

For DSO imaging, I would definitely get mono camera with filters due to longer sub-exposure times but like I said earlier, cooled cameras would be much better choice for DSO imaging.

 

I am a long time (5+ years) DSO imager and currently use QSI cooled mono camera with Astrodon filters and get great results. I just started to get interested in planetary imaging and I am starting with color version of ASI120MC-S (USB 3.0) and will see how this will turn out. Since my QSI camera has built-in filter wheel and odd-size 31mm filters and to use mono version of ASI camera (120 or 174), I would have to get new filter wheel AND a set filters because there is no separate filter wheel (as far as I know) that would accept 31mm filters and buying another set of filters is not exactly what I had in mind.

 

If you want to own only one camera for both planetary and DSO imaging, then ASI174 would be a better choice. For DSO imaging, I would image only bright DSOs so the exposure times would be shorter and don't forget to dither when capturing DSOs.

 

Peter



#13 freestar8n

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Posted 02 June 2015 - 05:35 PM

Any noise comparison should really measure everything in electrons.  It's hard to compare just images of sensor noise.

 

Things are more complicated if there is some kind of internal dark subtract with a lookup table - but it should still be possible to get an idea of the dark current and the pattern noise in electrons.

 

I would be surprised if there is any difference in the bias or dark current for a color vs. mono version of the same sensor.

 

Pt. Grey has some good data tables that include the 174 sensor and it stands out very well in terms of read noise and QE.  The qhy5l-ii is very good, and the 174 is even better by those metrics.  I don't recall measurements of dark current - but for these cameras without cooling I wouldn't really promote them for long exposure work - depending on the temperature.  But they can still do well for deep sky in short exposures of brighter targets.

 

That doesn't mean they couldn't do well for longer exposure - but if they do have non-negligible dark current and no cooling - that will be a fundamental limitation unless other noise sources like sky background dominate.

 

Will someone package the 174 in a camera with cooling?  I don't know.

 

Frank


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#14 Peter in Reno

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Posted 03 June 2015 - 03:12 PM

Things are more complicated if there is some kind of internal dark subtract with a lookup table - but it should still be possible to get an idea of the dark current and the pattern noise in electrons.

 

Frank

 

I asked this question at ASI's own forum and I got a different answer from the founder of ASI but his English is not perfect and I am not sure of his answer. I think he said that there is a look up table for hot pixels. See thread below:

 

http://zwoug.org/vie...php?f=21&t=2011

 

Peter



#15 drt

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Posted 18 December 2017 - 12:00 PM

Maybe this is wrong place, but I will ask anyway.
Is something wrong with my camera, ASI120mm-s?

I am a newbie in respect of ZWO cameras...

Attached Thumbnails

  • bad camera image sm.jpg

Edited by drt, 18 December 2017 - 02:19 PM.


#16 freestar8n

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Posted 18 December 2017 - 02:55 PM

I'm pretty sure that is just an artifact of a rolling shutter and different light sources flickering at different rates.

 

The room lights are at a lower frequency than the laptop display.

 

Try aiming the camera out the window at a daylight scene and I expect the banding will be gone.

 

So I think it is perfectly fine.

 

Frank




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