Minimum Exposure Time ASI178MC

rainer

Hi all,

I have a question related to my uncooled ASI178MC Camera, which I'm using in an AllSkyCam configuration.

Since I want to use the camera not only for Night-Exposures (this is already working nicely and I'm really happy with the Camera's features), but also at daylight, experimenting with HDR Imaging, I need very short exposure times to minimize overexposure for hdr imaging.

According to the camera control readouts I got from the SDK (I'm using the nice Python bindings by Steve Marple) and to the datasheet, the minimum exposure time is 32 microseconds.

However if I run a focus scale with e.g. 32, 50, 100 and 200 microseconds (see attached images, with number after underscore indicating the exposure time, the 50 microsecond image is not included because of the limitation on number of attachments, and the images are compressed from the original 48bit color png images to scaled down jpg images) only the 200 microsecond exposure is showing any difference in histogram and overall brightness.

It seems like the 32, 50, and 100 microsecond exposures are identical.

I tried already different capturing methods (e.g. snapshot and video capture) but to no avail.

Autoexposure and autogain is off. Gain is zero, Bandwidth setting does not change anything, Hardware bin is the default zero, HighSpeedMode is off, Monobin is zero as well, and any change to the Offset is not changing anything as well (as expected).

The attached images are taken with the "capture" routine of Steve's Library (see https://github.com/stevemarple/python-zwoasi/blob/master/zwoasi/__init__.py) and read into an numpy buffer for further processing, so timing should be not an issue as well.

I'm a bit at a loss, what else to try, any additional ideas?

Best regards,

Rainer Minixhofer

chad

Hi Rainer,

Thanks for your testing.

I used the raw16 to make a test with Sharpcap. it works fine. You can check the attachment. It shows the histogram at different exposure time.

Maybe you also could use Raw16 to make a test.

Thanks

Chad

rainer

Hi Chad,

thanks for your fast feedback. The Images are generated from RAW16, then they have been debayered and then saved into 16Bit PNG (since the PNGs are very large, I converted them to JPGs in my previous post). I could not attach the original PNGs, since they are too large for the attachment here in the forum. The luminance histograms of the 32, 50, 100 microsecond exposures are practically identical (average around 35.57, median 39). Could there be any issue in the SDK which is not happening in Sharpcap?

BTW, I'm using the color version of the ASI178 the MC and not an ASI178MM as you used, could this be an issue?

BR,

Rainer

chad

Hi Rainer，

You can use SharpCap with the same setting to take the images, and save them into fits. Then upload them to the dropbox, and send me the URL to me.

Or you can use Raw16 to save it and check the histogram. Maybe that also help.

For the current, I think it should be the same.

Thanks

Chad

rainer

Hi Chad,

I generated now two RAW16 FITS files with exposures 32, 71, 143 and 286 microseconds, and the histograms for 32, 71 and 143 are again practically identical. I'm still using the SDK since SharpCap is not available on Linux and the Camera is connected to a NanoPI which controls it.

The files are under

https://www.dropbox.com/s/kmmm5vpztfgxixe/analemma20190927110726_32.fits?dl=0

https://www.dropbox.com/s/veielwusn8opslo/analemma20190927110726_71.fits?dl=0

https://www.dropbox.com/s/mojb0i9qgwjwabp/analemma20190927110726_143.fits?dl=0

https://www.dropbox.com/s/5y2n8ga1o9s6wei/analemma20190927110726_286.fits?dl=0

Any ideas?

Best regards,

Rainer

chad

Hi Rainer,

Talked with my colleague, it might be the problem of USB bandwidth.

And I also tested it. It is possible.

On my side, I tested it with USB3.0 at 100 percent of USB bandwidth.

But if I tested it with USB2.0 at 40 percent of USB bandwidth, it have the same result like yours.

So if you are using the USB2.0, you can try USB3.0.

Thanks

Chad

rainer

Hi Chad

Thanks for the feedback. This could a possible explanation. I use an USB 3.0 Port with 40 Percent Datarate on a NanoPi but need to check if it's really on USB 3.0 speeds :-). The NanoPi hardware crashed with 100% speed but I did not try rates < 100%. I'll try it over the weekend and post the results.

Best,

Rainer

rainer

Hi Chad,

the ASI178MC was really running on USB 2.0 speed (Hi-Speed with 480 MBd) and not on USB 3.0 speed (SuperSpeed with 5000 MBd). I first thought it is related to the cable, but after hot-unplugging/replugging the camera on the same port it registered with SuperSpeed . It seems that during the bootup of the NanoPi M4, where the camera is connected to, the USB Port starts in a lower speed mode than after hot-plugging. I need to check if this is during the bootup sequence of the camera. I cannot afford hot-plugging when the camera is mounted in its watertight housing, so I have to find a programmatic approach to enforce USB 3.0...

Thanks for the hint on the USB speed though, I would have searched till today, without your feedback....

Rainer

rainer

Hi Chad,

just as a final information: I solved the issue now by implementing a PI controlled Hardware Switch, which switches the 5V supply of the USB 3.0 Port of the ASI178MC. Therefore I can just start the camera AFTER the PI has booted up correctly (the NanoPI has the USB 3.0 Port supply lines hardwired, so they cannot be switched through the kernel) by switching the Hardware Switch on.

Thanks again for the support, I hope this info helps others which have had similiar issues....

BR,

Rainer