Sensor analysis results

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Tiago Ferreira
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Sensor analysis results

#1

Post by Tiago Ferreira »

I did 2 sensor analysis in a row with my ASI294MC. The 1st at 30ºC and the 2nd at 37ºC ceteris paribus
Well, i use a cap over the sensor to reduce brightness so may had some brightness little variation too.
The results were different and the 2nd test tend to higher values on the different columns. Is this the impact of temperature difference? Should that difference make different results when doing brain/smart histogram? Or i just should ignore it?


Gain Value e/ADU Read Noise (e) Full Well (e) Relative Gain Rel. Gain (db) Dynamic Range (Stops)
0 3,891736059 7,672276273 63762,20359 1 0 13,0207592
50 2,184248643 6,785493432 35786,72976 1,781727585 5,016826077 12,36468336
59 1,987183299 6,724052089 32558,01118 1,95841826 5,838108994 12,24139405
61 1,937236998 6,688789372 31739,69098 2,008910661 6,059212469 12,21225535
100 1,243194017 6,163715292 20368,49077 3,130433389 9,912089342 11,69025124
119 1,001668341 5,990488167 16411,33411 3,885254129 11,78838861 11,41973133
121 0,858429775 1,774890675 14064,51343 4,533552044 13,12877211 12,95204186
150 0,617538817 1,680511558 10117,75598 6,30201042 15,98958234 12,55570126
200 0,345142337 1,500575438 5654,812046 11,27574234 21,04290286 11,87974751
250 0,197768221 1,416055641 3240,234525 19,67826807 25,87973745 11,16000457
300 0,110186628 1,310005845 1805,297714 35,319495 30,96028971 10,42844781
350 0,063579821 1,278743009 1041,691782 61,21023961 35,73648159 9,669986405
400 0,035744707 1,294826071 585,6412831 108,8758689 40,73863268 8,821115127
450 0,023220073 1,441114638 380,4376837 167,6022285 44,48559578 8,044331243
500 0,012179179 1,343630256 199,5436645 319,5401053 50,09050748 7,214424477




Gain Value e/ADU Read Noise (e) Full Well (e) Relative Gain Rel. Gain (db) Dynamic Range (Stops)
0 3,917030657 7,842379989 64176,63029 1 0 12,99846887
50 3,079648987 9,66763801 50456,969 1,271908154 2,08911503 12,34960247
59 2,754347765 9,41889906 45127,23378 1,422126395 3,058763942 12,22615229
61 2,687129772 9,369911128 44025,93419 1,457700591 3,273366598 12,19803063
100 1,727123422 8,703312711 28297,19015 2,267950632 7,112671937 11,66680655
119 1,400139827 8,515028421 22939,89093 2,797599627 8,935711227 11,39555957
121 1,200644138 2,517966796 19671,35356 3,262440995 10,27085332 12,93154935
150 0,86350051 2,367156413 14147,59235 4,536222751 13,13388745 12,5451139
200 0,48322719 2,133314806 7917,194278 8,105981493 18,17611216 11,85767666
250 0,275425347 1,973105874 4512,568892 14,22175081 23,0590613 11,15926487
300 0,153714761 1,846316663 2518,462639 25,48246271 28,12482795 10,4136776
350 0,087581285 1,757063383 1434,93177 44,72451697 33,01091318 9,673600189
400 0,048969374 1,781658617 802,3142292 79,98939562 38,06064831 8,814802645
450 0,028152903 1,760019377 461,2571634 139,134165 42,86867572 8,033836194
500 0,015728118 1,740401713 257,6894925 249,0463607 47,925604 7,210069559
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Re: Sensor analysis results

#2

Post by admin »

Hi,

the most likely cause of those figures is variations in the illumination level during the last stages ('measuring relative gain') of the analysis - this has led to the wrong relative gains and e/ADU being calculated for all the gain values above zero. I've certainly never noticed any strong influence of sensor temperature on the figures.

With the ZWO cameras, the gain value that you select is rougly 10 times the gain in dB - you can see this works for the first set of figures (dB gain is the last but one number), but doesn't work for the seconds set.

cheers,

Robin
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Tiago Ferreira
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Re: Sensor analysis results

#3

Post by Tiago Ferreira »

admin wrote: Sat Jul 03, 2021 9:19 pm Hi,

the most likely cause of those figures is variations in the illumination level during the last stages ('measuring relative gain') of the analysis - this has led to the wrong relative gains and e/ADU being calculated for all the gain values above zero. I've certainly never noticed any strong influence of sensor temperature on the figures.

With the ZWO cameras, the gain value that you select is rougly 10 times the gain in dB - you can see this works for the first set of figures (dB gain is the last but one number), but doesn't work for the seconds set.

cheers,

Robin
I've ran a new analysis with zwo asi294 and zwo asi224 this time with careful about the illumination. At the end the results on gain in db matched the 10x gain and also i've seen a sensor linear % above 90% and i remember that in the posted previous analysis it was less than 30% (that % that is above the final table but doesn't copy to clipboard). I have a feeling that this is important and that is connected with the previous poor results. Can you confirm that please?
I also kept the uv/ir cut filter during all analysis because it's always attached and i thought like if it was an original part of the cameras, which could be. Does this also make sense?
Also to have all the correct info about to use this tool can you tell me what read noise limit is suggested to use? I'm aware that this change the final results but not sure what to choose apart of the 10% default. I suppose, 10% or below it's better?
Youtube channel: https://youtube.com/@DobsonianPower

12" f/5 Dobsonian GSO
8" f/6 Dobsonian GSO
6" f/5 Dobsonian Go-To Virtuoso Gti
Dwarf II Smart Telescope
Geoptik Eartha Eq Platform
ZWO ASI224MC + ZWO ASI294MC
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Re: Sensor analysis results

#4

Post by admin »

Hi,

yes, a 30% linearity limit is also going to be linked to varying illumination levels. Basically the linearity check gradually turns up the exposure time and checks that the response of the camera is proportional to the amount of light being collected (which is proportional to the exposure time if the illumination is constant).

The % read noise limit is the additional % of noise you are prepared to accept in your final image in exchange for taking shorter sub exposures.

The minimum possible noise you could get would come from a single sub that covers the entire imaging session on the target. That would still have a certain noise level determined by the random arrival of photons on the camera pixels (and it would normally not be feasible, but lets not worry about that right now). If you set the read noise limit to 10% then you are saying that you are prepared to accept a final image with a noise level 10% higher than the absolute theoretical minimum from a single massively long exposure.

If you did the imaging both ways then your single massively long exposure would have a noise level of (say) 50, and your stack of lots of subs at the settings recommended by SharpCap set to 10% would have a noise level of 55. Can you notice 10% more noise? - not easily. Can you notice 1% more noise? - almost certainly not. Can you notice 50% more noise? probably... That's where the 10% default comes from - I suspect that choosing in the 5-10-20% range would be reasonable, anything outside that is probably not very useful.

cheers,

Robin
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