Author Topic: DSLR Sensor Parameters - questions concerning results (estimated thermal noise)  (Read 854 times)

Offline Peter S

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Hi,
following results for my sensor - I dont understand results concerning estimated thermal noise / skyfog noise.
results:
ISO speed: 1600
Image Size: 11608 x 8708
Bias frames exposure time: 1/4000 sec
Flat frames exposure time: 1/2000 sec
Dark frames exposure time: 30 sec
Light frames exposure time: 30 sec
Channel order:             []
Gain per channel(e/ADU):   [ 0.047, 0.047, 0.047, 0.047 ]
ISO for unit gain:         [ 75, 75, 75, 75 ]
Read Noise(e):             [ 1.24, 1.25, 1.25, 1.26 ]
Dark Current (e/pixel/sec) [ -0.0308, -0.0309, -0.031, -0.031 ]
Dark Current (e/pixel/sec) [ -0.0307, -0.0308, -0.0309, -0.0314 ]
Dark Current (e/pixel/sec) [ -0.03, -0.0298, -0.0301, -0.0304 ]
Dark Current (e/pixel/sec) [ -0.0297, -0.03, -0.0301, -0.0304 ]
Dark Current (e/pixel/sec) [ -0.0294, -0.0297, -0.0298, -0.0302 ]

Noise estimates for 30sec exposure
Read Noise(e):             [ 1.24, 1.25, 1.25, 1.26 ]
Thermal Noise(e):          [ -92233720368547760, -92233720368547760, -92233720368547760, -92233720368547760 ]
Skyfog Noise(e):           [ -92233720368547760, -92233720368547760, -92233720368547760, -92233720368547760 ]

Mean values in ADU
Bias Frame 1: [1025.2, 1025.1, 1025, 1025.1 ]
Bias Frame 2: [1025.2, 1025, 1025, 1025 ]
Flat Frame 1: [10217.2, 13880.2, 13899.5, 4960.4 ]
Flat Frame 2: [10330.2, 14040.5, 14059.9, 5010.3 ]
Dark Frame 1: [ 1025, 1025.1, 1025, 1024.8 ]
Dark Frame 6: [ 1026.4, 1026.5, 1026.4, 1026.5 ]
Light Frame 1: [1197.3, 1328.1, 1328.4, 1144.1 ]
Light Frame 2: [1196.4, 1325.7, 1326.5, 1143.8 ]

DSLR Sensor Parameters v0.0.6 Completed.

Info:
Sensor has an offset / Black level: 1024

Any ideas?

Peter

Offline sharkmelley

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I was responsible for that script.  There's actually a version 7 which you can find here and fixes a bug in the skyfog calculation:  https://pixinsight.com/forum/index.php?topic=10365.15

However the main problem is that it is calculating a negative dark current.  This will be because the standard deviation of the difference of a pair of dark frames is lower than the standard deviation of the difference of a pair of 2 bias frames. 

Why this is the case, I don't know.  From the 100Mpixel sensor size I'm guessing this might be a Phase One Trichromatic camera?  I wonder if the file format is being interpreted correctly or if some "cooking" of the raw files is taking place, for instance noise reduction on longer exposures?

Mark
Takahashi Epsilon 180ED
H-alpha modified Sony A7S
http://www.markshelley.co.uk/Astronomy/

Offline Peter S

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Mark,
I´ll try the new version!
...it´s the IQ3 100 (not trichromatic), auto darks were surpressed, no auto noise suppression.
but the sensor temperature rises between and during exposures.

Peter

Offline Peter S

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V7 does not change much,  but the results (dark current)  depend on which dark or light frames of a series I take, so it´s probably the rising temperature (?).

Bias frames exposure time: 1/4000 sec
Flat frames exposure time: 1/2000 sec
Dark frames exposure time: 30 sec
Light frames exposure time: 30 sec
Channel order:             []
Gain per channel(e/ADU):   [ 0.047, 0.047, 0.047, 0.047 ]
ISO for unit gain:         [ 75, 75, 75, 74 ]
Read Noise(e):             [ 1.25, 1.25, 1.25, 1.25 ]
Dark Current (e/pixel/sec) [ 0.1655, 0.1809, 0.1685, 0.1786 ]

Noise estimates for 30sec exposure
Read Noise(e):             [ 1.25, 1.25, 1.25, 1.25 ]
Thermal Noise(e):          [ 2.23, 2.33, 2.25, 2.31 ]
Skyfog Noise(e):           [ 2.69, 3.61, 3.62, 2.12 ]

Mean values in ADU
Bias Frame 1: [1025.2, 1025, 1025.1, 1025.2 ]
Bias Frame 2: [1025.3, 1025.2, 1025.1, 1025.1 ]
Flat Frame 1: [10345.7, 14075.4, 14095, 5026 ]
Flat Frame 2: [10466.9, 14247.7, 14267.4, 5079.5 ]
Dark Frame 1: [ 1061.6, 1065.7, 1062.1, 1067.3 ]
Dark Frame 2: [ 1064.5, 1068.8, 1065, 1070.5 ]
Light Frame 1: [1216.5, 1343.6, 1342, 1164 ]
Light Frame 2: [1216.4, 1343.8, 1342.3, 1164 ]
DSLR Sensor Parameters v0.0.7 Completed.

Peter