How do I (can I) use SC to test ASI294 linearity

[GaryS]

Is there a way in SC to do the above test and plot out the exposure time versus the ADU count?

Thanks!
Gary

[admin]

Hi,

in the most recent versions of SharpCap 3.2, the sensor analysis functionality does a linearity test. This generates a graph while it's in progress and a 'linear up to XX%' figure at the end. You do need to make sure that your light level is absolutely constant and that the selected area is of uniform brightness for this to give useful results though. If you do the analysis then a CSV file will be written to the desktop containing the exposure lengths and brightness levels observed during the measurement.

Cheers, Robin

[GaryS]

Thanks very much Robin. Will it report brightness in ADU? (See the attached procedure that I'm trying to follow)
Gary

Screenshot (383).png (78.94 KiB) Viewed 1347 times

[admin]

Hi,

yes, the brightness will be measured in ADU, although I can't remember off the top of my head whether it's true ADU (14 bit) or ADU that been scaled up to the full 16 bit range – since the scaling is only a matter of multiplying by constant factor it won't make any difference to the final results.

Cheers, Robin

[GaryS]

Thank you Robin. That’s a big help.
Gary

[GaryS]

So Robin, I've now tried 4 runs at the sensor analysis and it ends up failing every time. I've attached some screenshots during various phases of my 4 attempts. Hopefully you can tell from these what might be going wrong.

Here are the attachment descriptions in order:

1. Indication that its ok to start (note the height of the graph. there was a note it should be 65% high but no way could I adjust to achieve that)
2. Linearity is looking fine (I think)
3. Warning that Exposure is too low
4. Sensor Analysis failed

My process involved a 3 Brightness-level LED screen used for tracing and artwork on the floor with the telescope facing down with the open end about 20" above it.
The Camera was an ASI294 MC and I used the opaque filter in the filter wheel for the Dark analysis.

The analysis seemed to run fine(target brightness achieved") through the Light and Dark analysis but when I got into whatever runs after that, it kept on going with the analysis but eventually failed after telling me the exposures were getting too long. Each time I retried and with a higher exposure, the initial part of the analysis wanted it darker, so, ultimately I concluded that no single light level would work all they way through the analysis. Is this the case? Nothing was mentioned about that so I had no idea how to handle it or when was the time to change the lighting. It seems so fussy about the light levels that it made me thing there was something else wrong so, sadly, I turn to you once again for help.

If you need further info from me on the process or have ideas that I can try to see if I can get the analysis to work, please let me know.
Cheers,
Gary

[admin]

Hi,

so, firstly if you have the SharpCap log from the failed runs then please post it here or share it with me some other way (logs can be found in %localappdata%\SharpCap\logs).

A couple of things that I noticed from your screenshots

1) There are dropped frames reported in the frame counter in the bottom left - this could be a problem - if these are happening during the analysis then it would be good to work out why and cure that problem before retrying

2) Just checking that you are not altering the light brightness during the analysis - it's designed around a contstant brightness throughout - small changes will not be a problem, but big ones could be, since the early stages calibrate the gain range to be measured based on the exposure time.

3) it's odd that it fails at gain 121 - normally that would have fairly short exposures (getting shorter with every gain increment). I wonder if the camera is not delivering brighter frames for some reason as the exposure is increased (possibly linked to the dropped frames)

cheers,

Robin

[GaryS]

Sorry Robin, I have no idea how to find the logs from the link you provided. Yours is the only application I use the PC for - I use a Mac for all else. I've search all the folders I can find with misc items in them and I see nothing about SC or Logs. I followed the path you provided which ended as: C:\Users\Default.migrated\AppData\Local\Microsoft\Windows. As you see there was nothing at the end of the path on SC logs.

ASI294MC
So, continuing the Quest: I took the 294 off the scope and tried many sensor analysis runs again with it facing onto my illuminated panel. No matter what I did with light levels I was unable to get the sensor analysis tool to work with this camera. I used multiple layers of white paper to try to dim the screen when it told me it was to bright. I removed some/all of them when it told me the level was too dim-nothing worked. I had no problem getting through the first two steps of the analysis but after I removed the cover from the camera for the final step, it failed every time...no matter what level of lighting the camera was seeing. As you'll see below, I had no problem running the analysis for the ASI 178MM so the situation with the ASI 294 is incredibly frustrating as its my main camera.

ASI178MM
Anyway, I manged to get the Sensor Analysis to run for the ASI 178 MM. The problem I have with the results is that I have no idea what it tells me other than the Unity Gain is negative for the 14 Bit Mono setting (see attached 1) and unity gain is about 360 with the 8 Bit Mono setting (see attached 2). The negative gain for 14 Bit seems wrong as does the 360 gain for the 8 Bit.

Attach 1 ASI178MM 14 Bit Sensor Analysis(408).png (352.66 KiB) Viewed 1222 times

Attach 2 ASI178MM 8 Bit Sensor Analysis(403).png (329.38 KiB) Viewed 1222 times

I will try again to find the log somewhere in this pc. In the meantime, anything you can add to help me get these sensor analyses done right and explain what info is useful there, would be very much appreciated.
Enjoy the weekend!
Gary

[oopfan]

Gary,

I recognize the document in the screenshot of your original post: AAVSO's CCD Photometry Guide.

I agree with Robin. You need a very stable light source. I tried an Electroluminescent Panel but found that the brightness varied. I ended up using an LCD monitor. I've attached results for a run at several gain settings.

I do things "old school," mostly because I'm old. It gets the job done, plus I have complete control. The only time I seek out specialized software is if I find myself doing the same thing repeatedly, day in and day out. Even then, I'll opt to write a script using existing reliable software like SharpCap. Robin writes great software but, in my opinion, there is greater opportunity to learn new things when you choose "old school".

Brian

Brians Altair 290M LCG Linearity.jpg (252.58 KiB) Viewed 1215 times

[GaryS]

Hi Brian, and thanks for posting your thoughts on the topic. I did start out based on doing the aavso linearity test but now I'm in mid stream trying to get Robins 'sensor analysis' to work for my two current cameras.

I'm hoping Robin can help me with the odd data I got for the completed sensor analysis on my ASI178MM and also help me get the sensor test to work at all on the ASI294 MC.
Take Care.
Gary