Sorting out divergent Sensor Analyses - ASI 294MC

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GaryS
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Sorting out divergent Sensor Analyses - ASI 294MC

#1

Post by GaryS »

Hi All;
I ran the sensor analysis on the camera above mostly to understand the range of linearity between increasing exposures and resulting mean ADU counts. This info is important in imaging for photometry to avoid non-linear regions and avoid saturation of key stars.

The two Sensor Reports I got from two sequential runs through the analysis gave me identical results( a good things) AND surprisingly low linearity for this sensor at 30%( a bad thing). I'm not sure how to interpret the exact region of linearity( exposure versus adu count) since its given in '%' and nowhere is there a plot or data comparing ADU's with exposure time. For comparison, I've attached a similar sensor report for the ASI 178MM which states 98% linearity

Is there a better way to generate a simple plot of the sensor's ADU response to increasing exposures running from 5 secs on up to 100 seconds?

thanks greatly for any assistance sorting this out!
Gary


Analysis ASI 294 MC
294mc SC Sensor Report 1.png
294mc SC Sensor Report 1.png (126.04 KiB) Viewed 525 times
Analysis ASI 178 MM
294mc SC Sensor Report 1.png
294mc SC Sensor Report 1.png (126.04 KiB) Viewed 525 times
Attachments
178mm SC Sensor Report Screen.JPG
178mm SC Sensor Report Screen.JPG (150.41 KiB) Viewed 525 times
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admin
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Re: Sorting out divergent Sensor Analyses - ASI 294MC

#2

Post by admin »

Hi,

when you run the analysis, SharpCap should save a CSV file on your desktop containing the sensor linearity data - named something like 'SensorResponse_ALTAIRGP224C_RAW12.csv'. The two columns are exposure (in ms) and the response from the sensor (% of max ADU).

Note that the most likely cause of poor measurements are fluctuations in the illumination brightness during the measurement procedure - to get good results the illumination levels must be constant.

cheers,

Robin
GaryS
Posts: 175
Joined: Sun Mar 31, 2019 5:18 pm
Location: Boston, USA/Jackson Hole, USA

Re: Sorting out divergent Sensor Analyses - ASI 294MC

#3

Post by GaryS »

Thank you Robin.

I found the table amongst the litter on my screen - had not realized it was produced. Several questions:

1. The exposures only ran from 22ms to 1.7 sec. is there some way to create a linearity test from something like 1 - 120 seconds?

2. Regarding the % of signal (ADU), it runs from 1.5% to 76%. The sensor analysis gave me a FW depth value of about 68.5k adu (at 0 gain) while the ZWO spec is 63.7k adu. What do you make of this difference?

3. Can I rely on multiplying the % by 68.5k adu or should I multiply it by the ZWO value of 63.7k adu?

Again, thank you for your much-appreciated responsiveness!
Gary
GaryS
Posts: 175
Joined: Sun Mar 31, 2019 5:18 pm
Location: Boston, USA/Jackson Hole, USA

Re: Sorting out divergent Sensor Analyses - ASI 294MC

#4

Post by GaryS »

Also.....I used SC to determine the mean adu based on a series of exposures as I mentioned before. the sensor report indicated 30% linearity so I thought you'd like to see the table and graph that I generated with SC's series of exposures.
Gary
Linearity Test of ASI 294MC.png
Linearity Test of ASI 294MC.png (62.04 KiB) Viewed 521 times
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Re: Sorting out divergent Sensor Analyses - ASI 294MC

#5

Post by admin »

Hi,

You will have to do your own measurements if you want to test with longer exposures - the auto measurement is set up to try to keep all the exposure times under 2s if at all possible.

The data will stop when SharpCap detects significant non-linearity - so in your case by the time it had measured at 76% brightness, it found non-linearity, so stopped the measurement rather than continue. The goal here is to keep the sensor analysis fairly quick.

With regard to the FWD measurement, this is based on the e/ADU measurement for minimum gain, so variation in that would lead to variation in FWD. I would re-run the analysis a few times to see if it always reports ~68k or if there is significant variability. Personally I would probably use SharpCap's value if it is consistent.

I suspect that your linearity measurement is being affected by the illumination of the sensor not being quite even - that means that as you approach saturation some areas will saturate earlier than others, leading to the sort of roll over that you see above 40s. Try testing with a small area selected using the selection area tool - that should give much less of that sort of problem.

It just happens that I have a ZWO 294MM sitting on my desk at the moment, so I will try analysis on that to see what happens.

cheers,

Roibn
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Re: Sorting out divergent Sensor Analyses - ASI 294MC

#6

Post by admin »

Hi,

in excellent conditions for analysis (natural light, clear sky day, no clouds), I got the following results
Capture.JPG
Capture.JPG (87.24 KiB) Viewed 512 times
That all looks fine both from the point of view of the sensor parameters (noise, e/ADU etc) and the linearity measurement.

cheers,

Robin
Attachments
SensorResponse_ZWO ASI294MM Pro_MONO16.csv
(917 Bytes) Downloaded 45 times
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