I've loaded data from ZWO ASI294MC Pro and ZWO ASI120mm-mini

Hi Richard,

I've finished processing the data for your four cameras. I uploaded text files with results into each of your camera folders on the google share. Take a look if you are curious.

This had been a very productive exercise for me. I've made notes of a number of changes I plan to make to my calculation function.

For the most part my tool seems to be producing reasonable values. The only result I question is for the FLI Kepler, mainly because there was pattern noise in some input files, and the read noise that my tool computed was a bit higher than the value I found reported on the manufacturers site. (I actually ran a 2nd test for this camera where I selected different region to analyze, but the result was not substantially better.

I plan to make some custom camera data files for you, in case you want to use the exposure calculator. But the Moravian camera might pose a problem for the exposure calculator. My design in the exposure calculator assumed that CCD cameras do not have an ability to select gain. But this camera seems to have discrete gain values that can be chosen. So, in a way it behaves rather like a DLSR that has discrete ISO settings. So I may need to make a change to the exposure calculator to handle this type of CCD camera.

Thanks again for providing the files.

Actually the Moravian is a CMOS camera, not CCD. I know that INDI treats them all as CCD or DSLR, but it's quite common for CMOS ones to have selectable gain. The important point about it is that the "gain" is not actually gain but a look-up table entry from where the gain is read. That's why I attached the page from the user manual.

I agree the Kepler has a weird fixed pattern component. It can be calibrated out, but doesn't look good in the pre-calibration frames.

Did you find the photon transfer curves of any use? If so, I can present the data I already collected for the Kepler and QSI in the same form. These may be doing something similar to you, but over a wide range of flat exposures, and dark exposures too as a variant.

Cheers,
Richard

Hi quick question why exposure time is in ms for me when i saw sec on several screens shared.
where i can select exposure time format

Hi Vera,

The calculator should only display, exposures in seconds. But the calculation can produce extreme exposure times, both very short and very long, depending upon the inputs.
Can you share a screen shot of the calculator?

Hi Richard,

For the Moravian, I made a small adjustment to the output from my tool to include the dynamic range value in both raw (no units), and in dB. So that it can be better compared to the information in the charts you provided.

My computed values are generally the same, as what I find in the charts. But there is a difference between my computation of Full Well, and that shown in the charts.The calculation for full well is gain (e-/adu) x max adu. But I use 65536 (on a 16-bit readout) as the max adu, but the charts seem to using 64000. Do you think that the reduction is to account for thermal noise, or maybe something else? (My tool does not yet consider thermal noise).

But I use 65536 (on a 16-bit readout) as the max adu, but the charts seem to using 64000. Do you think that the reduction is to account for thermal noise, or maybe something else? (My tool does not yet consider thermal noise).

It's a bit subjective. The fixed pattern and shot noise fall off as full-well is approached (since there's no dynamic range left for the positive excursions of the noisy signal). So on the photon transfer plots you do see this fall-off. So you could assign the max value of the 16-bit ADC as the full-well capacity, or you could back it off a bit -- given the noise signal it's difficult to say exactly where it is.

I used 64000 in the plots but 65536 is equally valid. In either case the observed noise is significantly reduced, as you see in the plots.

Cheers,
Richard

Hi Vladimir,

I ran my tool on the data from both your cameras, but I had to spend some extra time reviewing the results. I've uploaded some files to the Google share in case you are interested it seeing what my tool produced.

But here is a summary...

For the ASI-120MM:
1) The results from my tool seem reasonable, but these calculations do not match the ZWO Documentation for this camera very well.
My tool calculated higher read noise at lower gain settings than what ZWO graphs show. But my tool calculated lower read noise at the gains of 80 to 100, than than what ZWO graphs show.

2) The ZWO documents show several steps in the read noise values. My understanding is that these steps usually caused by timing changes in the camera read-out circuitry. But the steps are occurring between the gain values of the images that we used for the analysis. So the results from my tool cannot "see" exactly where these steps occur. (This is expected, and when I develop the process to automate the capturing of images to be analyzed, I will need to detect where these steps occur).


For the ASI-294MC Pro:
My results are very different from the ZWO Documentation. Most noticeable is the calculation that my tool produced from the images at Gain value 50, which are very different from ZWO documentation. The calculation for Gain (e-/ADU) is lower that I would expect. This result causes the calculation of the Read Noise (-e) to be much lower. (This is apparent in the charts from the spreadsheet I uploaded).

I've been working to analyze the source of this discrepancy, and found that in the calculation of the Gain (e-/ADU), part of numerator in calculation, (the mean value of the sum of the flat pixel data), had fallen slightly, while part of the denominator of the calculation, (the standard deviation of the difference of the flat pixel data), rose abruptly. This produced a much lower than expected Gain (e-/ADU) for the images at Gain value 50. I will continue to analyze this, to determine whether my code has some fault.

Thanks again for providing the data

Hi
strange: now we see them in second (I was almost sure to see them seen in ms) ??

quick question , on the screen shot i have used a Filter norrow band - Optolong L-Extreme 7nm.
do i need to use 7 on the Filter Bandwith value as a value ?
is it the case in my example this means that it would take a picture = 1550 sec = 26 mn ?
i'm wrong ?

I believe the the l-extreme has two bands that are each 7nm. So you want to add them together, use 14nm for the exposure calculator.
But even with 14 you may have a longer exposure time than you would prefer to use, due to limitations in guiding etc.

Hi Vera,
I was travelling when I replied earlier, (using my phone and did not have access to a computer with KStars). So I thought I should give a bit more information to you now that I'm back from my trip.

I would recommend that you move the gain a little bit higher, maybe to 104. This is because the data we use for camera read noise is from graphs in ZWO documentation. But a specific camera might not have that "step" in the read noise exactly at gain 100. So to be certain that you are beyond that step and are really getting the lower read noise, then you need to give a little margin for variations in camera manufacturing.

So with the filter set to 14 nm, the exposure is still fairly long (about 770 seconds). That would be the exposure time from applying the standard noise increase % that Dr Glover recommended. That nearly 13 minute exposure should give an excellent result, because it has great amount of time, and not much noise (time / noise ratio is about 94). But if you would prefer to run a lower exposure time, (worries about guiding, or air traffic, satellites, etc), then you can raise the noise increase %. For example with gain at 104, and Noise increase % at 12.4, the calculation should show an exposure time of about 300 seconds. In your circumstances this should still produce a very good exposure (time / noise ratio is about 57).

Then you can try adjusting the Time/Noise ratio in the stacking calculation to see how many exposures are needed in stacking. Let's assume you are willing to spend about 3 hours imaging. If you are using 770 second exposures, you can reach a Time/Noise ratio of 352 with 14 exposures (just under 3 hours of total integration time). But to reach that same 352 time/noise ratio with the 300 second sub-exposures you would need 38 exposures (about 3 hours 10 minutes of total integration time).

Hi, Joseph!

I read that asi294mc has problems with shutter speeds shorter than 1 second. And many owners of this camera recommend taking flat frames with exposure of about 3 seconds and dark flat frames rather than a biases. But this shouldn't happen with asi120mm. Maybe I did something wrong? if it need i'll retake frames.