Sensor Analysis no unity gain

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fmoraes
Posts: 3
Joined: Sat Jul 03, 2021 4:02 pm

Sensor Analysis no unity gain

#1

Post by fmoraes »

I was trying the sensor analysis on the ASI178MC. I put a white shirt over the telescope to reduce the daylight brightness and ran the analysis. Here are the results:

Code: Select all

Gain Value	e/ADU	Read Noise (e)	Full Well (e)	Relative Gain 	Rel. Gain (db)	Dynamic Range (Stops)
0	0.972874271359019	2.3083684902392	15939.5720619462	1	0	12.75345173347
25	0.729829281015708	2.17224724486301	11957.5229401614	1.33301622265013	2.49670869517233	12.4264426188189
50	0.548901086162468	2.04324891194984	8993.19539568588	1.77240361858395	4.97125256054104	12.1037531329603
59	0.495308168413743	1.99523039225058	8115.12903129077	1.96417974384455	5.86362455891662	11.9898429723701
61	0.483684676002238	1.97851925716435	7924.68973162067	2.01138121513388	6.06988779621025	11.9677176291527
75	0.412555479837156	1.92556387194396	6759.30898165197	2.35816591684355	7.45148716220982	11.7773790701001
100	0.309889832100756	1.82836100513054	5077.23500913879	3.13941978916785	9.93698782995904	11.4392763691528
119	0.248973267511329	1.74715581195931	4079.17801490562	3.9075450994543	11.8380799837598	11.1890544781938
121	0.243427727363356	1.73720463391927	3988.31988512122	3.99656309450256	12.0337334729939	11.1647977048538
125	0.233224741507915	1.73478156507148	3821.15416486568	4.17140250673619	12.4056419557298	11.1050387318446
150	0.174799273112924	1.64204368244363	2863.91129068214	5.5656654288861	14.9103419172303	10.7682785837454
175	0.131649681411172	1.58074197068611	2156.94838024063	7.38987182445595	17.3727381145427	10.4141740437958
200	0.0986881943848764	1.52186565974316	1616.90737680182	9.85806131546883	19.875830301302	10.0531803093867
225	0.0744540249046975	1.49129012478996	1219.85474403856	13.0667787618509	22.3233707594513	9.67593269595781
250	0.0557381888264489	1.45645324501028	913.214485732539	17.4543574494005	24.8380773135727	9.29235054516293
275	0.041715530380532	1.4355286982872	683.467249754636	23.3216325546959	27.3551789703496	8.89514622610718
300	0.0310119321512041	1.42541103734259	508.099496365327	31.3709660725298	29.9305578610499	8.47758922319331
325	0.0232952504870756	1.41931940589145	381.669383980247	41.7627735704656	32.4157866707409	8.0709803613195
350	0.0176450779784594	1.43588015879135	289.096957599079	55.1357309129874	34.8286627244381	7.65347427182952
375	0.0132433682794789	1.43006106287449	216.979345890983	73.4612411909227	37.3211652370096	7.24533715921154
400	0.00993818907213419	1.43015344094006	162.827289757847	97.8925098222243	39.8149892666406	6.83102876264835
425	0.00734612226071232	1.40161307188322	120.358867119511	132.433716297104	42.439971324078	6.42411048708264
450	0.00576115899923696	1.4550388982615	94.3908290434983	168.86780446224	44.5509371385829	6.01951706797986
I was expecting unity gain to be somewhere around 250 but it seems to not show that as possibility even at 0 gain. Is my daylight source too bright for the measurement?
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Re: Sensor Analysis no unity gain

#2

Post by admin »

Hi,

the figures you have look correct to me - this particular sensor (IMX178) does not have a unity gain point as the number of possible pixel values (16384 for a 14 bit ADC) exceeds the full well depth (~15000-16000e).

My opinion is that there is not really anything special about unity gain anyway. For instance lets look at a different sensor that does have a unity gain point - pick the IMX183 in this case.

Unity gain on the 183 occurs at about 12dB of gain, and at that level the read noise is about 2.1e.

To take a reasonable deep sky sub-exposure at that gain level, you would want to collect at least 40 electrons in the darkest parts of the image to ensure that the read noise is not a major factor in the final noise level when you stack (see viewtopic.php?f=35&t=456). At 40e, the random noise in each pixel is about 6.5e. So, when your pixel values are varying by more than +/- 6e due to random fluctiations, why would it really matter whether you are measuring at 1e = 1 ADU or not? Everything down around the 1e scale is noise...

cheers,

Robin
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